path: root/SOURCES/scx-kernel.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Jan200101 <sentrycraft123@gmail.com>
Date: Wed, 17 Jul 2024 14:30:16 +0200
Subject: [PATCH] scx

Signed-off-by: Jan200101 <sentrycraft123@gmail.com>
---
 Documentation/scheduler/index.rst             |    1 +
 Documentation/scheduler/sched-ext.rst         |  316 +
 MAINTAINERS                                   |   13 +
 include/asm-generic/vmlinux.lds.h             |    1 +
 include/linux/cgroup.h                        |    4 +-
 include/linux/sched.h                         |    5 +
 include/linux/sched/ext.h                     |  206 +
 include/linux/sched/task.h                    |    3 +-
 include/trace/events/sched_ext.h              |   32 +
 include/uapi/linux/sched.h                    |    1 +
 init/init_task.c                              |   12 +
 kernel/Kconfig.preempt                        |   26 +-
 kernel/fork.c                                 |   17 +-
 kernel/sched/build_policy.c                   |   10 +
 kernel/sched/core.c                           |  250 +-
 kernel/sched/cpufreq_schedutil.c              |   50 +-
 kernel/sched/debug.c                          |    3 +
 kernel/sched/ext.c                            | 6537 +++++++++++++++++
 kernel/sched/ext.h                            |   69 +
 kernel/sched/fair.c                           |   27 +-
 kernel/sched/idle.c                           |    2 +
 kernel/sched/sched.h                          |  171 +-
 lib/dump_stack.c                              |    1 +
 tools/Makefile                                |   10 +-
 tools/sched_ext/.gitignore                    |    2 +
 tools/sched_ext/Makefile                      |  246 +
 tools/sched_ext/README.md                     |  258 +
 .../sched_ext/include/bpf-compat/gnu/stubs.h  |   11 +
 tools/sched_ext/include/scx/common.bpf.h      |  401 +
 tools/sched_ext/include/scx/common.h          |   75 +
 tools/sched_ext/include/scx/compat.bpf.h      |   28 +
 tools/sched_ext/include/scx/compat.h          |  187 +
 tools/sched_ext/include/scx/user_exit_info.h  |  111 +
 tools/sched_ext/scx_central.bpf.c             |  361 +
 tools/sched_ext/scx_central.c                 |  135 +
 tools/sched_ext/scx_qmap.bpf.c                |  706 ++
 tools/sched_ext/scx_qmap.c                    |  144 +
 tools/sched_ext/scx_show_state.py             |   39 +
 tools/sched_ext/scx_simple.bpf.c              |  156 +
 tools/sched_ext/scx_simple.c                  |  107 +
 tools/testing/selftests/sched_ext/.gitignore  |    6 +
 tools/testing/selftests/sched_ext/Makefile    |  218 +
 tools/testing/selftests/sched_ext/config      |    9 +
 .../selftests/sched_ext/create_dsq.bpf.c      |   58 +
 .../testing/selftests/sched_ext/create_dsq.c  |   57 +
 .../sched_ext/ddsp_bogus_dsq_fail.bpf.c       |   42 +
 .../selftests/sched_ext/ddsp_bogus_dsq_fail.c |   57 +
 .../sched_ext/ddsp_vtimelocal_fail.bpf.c      |   39 +
 .../sched_ext/ddsp_vtimelocal_fail.c          |   56 +
 .../selftests/sched_ext/dsp_local_on.bpf.c    |   65 +
 .../selftests/sched_ext/dsp_local_on.c        |   58 +
 .../sched_ext/enq_last_no_enq_fails.bpf.c     |   21 +
 .../sched_ext/enq_last_no_enq_fails.c         |   60 +
 .../sched_ext/enq_select_cpu_fails.bpf.c      |   43 +
 .../sched_ext/enq_select_cpu_fails.c          |   61 +
 tools/testing/selftests/sched_ext/exit.bpf.c  |   84 +
 tools/testing/selftests/sched_ext/exit.c      |   55 +
 tools/testing/selftests/sched_ext/exit_test.h |   20 +
 .../testing/selftests/sched_ext/hotplug.bpf.c |   61 +
 tools/testing/selftests/sched_ext/hotplug.c   |  168 +
 .../selftests/sched_ext/hotplug_test.h        |   15 +
 .../sched_ext/init_enable_count.bpf.c         |   53 +
 .../selftests/sched_ext/init_enable_count.c   |  166 +
 .../testing/selftests/sched_ext/maximal.bpf.c |  132 +
 tools/testing/selftests/sched_ext/maximal.c   |   51 +
 .../selftests/sched_ext/maybe_null.bpf.c      |   36 +
 .../testing/selftests/sched_ext/maybe_null.c  |   49 +
 .../sched_ext/maybe_null_fail_dsp.bpf.c       |   25 +
 .../sched_ext/maybe_null_fail_yld.bpf.c       |   28 +
 .../testing/selftests/sched_ext/minimal.bpf.c |   21 +
 tools/testing/selftests/sched_ext/minimal.c   |   58 +
 .../selftests/sched_ext/prog_run.bpf.c        |   32 +
 tools/testing/selftests/sched_ext/prog_run.c  |   78 +
 .../testing/selftests/sched_ext/reload_loop.c |   75 +
 tools/testing/selftests/sched_ext/runner.c    |  201 +
 tools/testing/selftests/sched_ext/scx_test.h  |  131 +
 .../selftests/sched_ext/select_cpu_dfl.bpf.c  |   40 +
 .../selftests/sched_ext/select_cpu_dfl.c      |   72 +
 .../sched_ext/select_cpu_dfl_nodispatch.bpf.c |   89 +
 .../sched_ext/select_cpu_dfl_nodispatch.c     |   72 +
 .../sched_ext/select_cpu_dispatch.bpf.c       |   41 +
 .../selftests/sched_ext/select_cpu_dispatch.c |   70 +
 .../select_cpu_dispatch_bad_dsq.bpf.c         |   37 +
 .../sched_ext/select_cpu_dispatch_bad_dsq.c   |   56 +
 .../select_cpu_dispatch_dbl_dsp.bpf.c         |   38 +
 .../sched_ext/select_cpu_dispatch_dbl_dsp.c   |   56 +
 .../sched_ext/select_cpu_vtime.bpf.c          |   92 +
 .../selftests/sched_ext/select_cpu_vtime.c    |   59 +
 .../selftests/sched_ext/test_example.c        |   49 +
 tools/testing/selftests/sched_ext/util.c      |   71 +
 tools/testing/selftests/sched_ext/util.h      |   13 +
 91 files changed, 13860 insertions(+), 118 deletions(-)
 create mode 100644 Documentation/scheduler/sched-ext.rst
 create mode 100644 include/linux/sched/ext.h
 create mode 100644 include/trace/events/sched_ext.h
 create mode 100644 kernel/sched/ext.c
 create mode 100644 kernel/sched/ext.h
 create mode 100644 tools/sched_ext/.gitignore
 create mode 100644 tools/sched_ext/Makefile
 create mode 100644 tools/sched_ext/README.md
 create mode 100644 tools/sched_ext/include/bpf-compat/gnu/stubs.h
 create mode 100644 tools/sched_ext/include/scx/common.bpf.h
 create mode 100644 tools/sched_ext/include/scx/common.h
 create mode 100644 tools/sched_ext/include/scx/compat.bpf.h
 create mode 100644 tools/sched_ext/include/scx/compat.h
 create mode 100644 tools/sched_ext/include/scx/user_exit_info.h
 create mode 100644 tools/sched_ext/scx_central.bpf.c
 create mode 100644 tools/sched_ext/scx_central.c
 create mode 100644 tools/sched_ext/scx_qmap.bpf.c
 create mode 100644 tools/sched_ext/scx_qmap.c
 create mode 100644 tools/sched_ext/scx_show_state.py
 create mode 100644 tools/sched_ext/scx_simple.bpf.c
 create mode 100644 tools/sched_ext/scx_simple.c
 create mode 100644 tools/testing/selftests/sched_ext/.gitignore
 create mode 100644 tools/testing/selftests/sched_ext/Makefile
 create mode 100644 tools/testing/selftests/sched_ext/config
 create mode 100644 tools/testing/selftests/sched_ext/create_dsq.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/create_dsq.c
 create mode 100644 tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.c
 create mode 100644 tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.c
 create mode 100644 tools/testing/selftests/sched_ext/dsp_local_on.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/dsp_local_on.c
 create mode 100644 tools/testing/selftests/sched_ext/enq_last_no_enq_fails.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/enq_last_no_enq_fails.c
 create mode 100644 tools/testing/selftests/sched_ext/enq_select_cpu_fails.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/enq_select_cpu_fails.c
 create mode 100644 tools/testing/selftests/sched_ext/exit.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/exit.c
 create mode 100644 tools/testing/selftests/sched_ext/exit_test.h
 create mode 100644 tools/testing/selftests/sched_ext/hotplug.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/hotplug.c
 create mode 100644 tools/testing/selftests/sched_ext/hotplug_test.h
 create mode 100644 tools/testing/selftests/sched_ext/init_enable_count.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/init_enable_count.c
 create mode 100644 tools/testing/selftests/sched_ext/maximal.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/maximal.c
 create mode 100644 tools/testing/selftests/sched_ext/maybe_null.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/maybe_null.c
 create mode 100644 tools/testing/selftests/sched_ext/maybe_null_fail_dsp.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/maybe_null_fail_yld.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/minimal.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/minimal.c
 create mode 100644 tools/testing/selftests/sched_ext/prog_run.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/prog_run.c
 create mode 100644 tools/testing/selftests/sched_ext/reload_loop.c
 create mode 100644 tools/testing/selftests/sched_ext/runner.c
 create mode 100644 tools/testing/selftests/sched_ext/scx_test.h
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dfl.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dfl.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dispatch.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dispatch.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c
 create mode 100644 tools/testing/selftests/sched_ext/select_cpu_vtime.c
 create mode 100644 tools/testing/selftests/sched_ext/test_example.c
 create mode 100644 tools/testing/selftests/sched_ext/util.c
 create mode 100644 tools/testing/selftests/sched_ext/util.h

diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst
index 43bd8a145b7a..0611dc3dda8e 100644
--- a/Documentation/scheduler/index.rst
+++ b/Documentation/scheduler/index.rst
@@ -20,6 +20,7 @@ Scheduler
     sched-nice-design
     sched-rt-group
     sched-stats
+    sched-ext
     sched-debug
 
     text_files
diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst
new file mode 100644
index 000000000000..a707d2181a77
--- /dev/null
+++ b/Documentation/scheduler/sched-ext.rst
@@ -0,0 +1,316 @@
+==========================
+Extensible Scheduler Class
+==========================
+
+sched_ext is a scheduler class whose behavior can be defined by a set of BPF
+programs - the BPF scheduler.
+
+* sched_ext exports a full scheduling interface so that any scheduling
+  algorithm can be implemented on top.
+
+* The BPF scheduler can group CPUs however it sees fit and schedule them
+  together, as tasks aren't tied to specific CPUs at the time of wakeup.
+
+* The BPF scheduler can be turned on and off dynamically anytime.
+
+* The system integrity is maintained no matter what the BPF scheduler does.
+  The default scheduling behavior is restored anytime an error is detected,
+  a runnable task stalls, or on invoking the SysRq key sequence
+  :kbd:`SysRq-S`.
+
+* When the BPF scheduler triggers an error, debug information is dumped to
+  aid debugging. The debug dump is passed to and printed out by the
+  scheduler binary. The debug dump can also be accessed through the
+  `sched_ext_dump` tracepoint. The SysRq key sequence :kbd:`SysRq-D`
+  triggers a debug dump. This doesn't terminate the BPF scheduler and can
+  only be read through the tracepoint.
+
+Switching to and from sched_ext
+===============================
+
+``CONFIG_SCHED_CLASS_EXT`` is the config option to enable sched_ext and
+``tools/sched_ext`` contains the example schedulers. The following config
+options should be enabled to use sched_ext:
+
+.. code-block:: none
+
+    CONFIG_BPF=y
+    CONFIG_SCHED_CLASS_EXT=y
+    CONFIG_BPF_SYSCALL=y
+    CONFIG_BPF_JIT=y
+    CONFIG_DEBUG_INFO_BTF=y
+    CONFIG_BPF_JIT_ALWAYS_ON=y
+    CONFIG_BPF_JIT_DEFAULT_ON=y
+    CONFIG_PAHOLE_HAS_SPLIT_BTF=y
+    CONFIG_PAHOLE_HAS_BTF_TAG=y
+
+sched_ext is used only when the BPF scheduler is loaded and running.
+
+If a task explicitly sets its scheduling policy to ``SCHED_EXT``, it will be
+treated as ``SCHED_NORMAL`` and scheduled by CFS until the BPF scheduler is
+loaded.
+
+When the BPF scheduler is loaded and ``SCX_OPS_SWITCH_PARTIAL`` is not set
+in ``ops->flags``, all ``SCHED_NORMAL``, ``SCHED_BATCH``, ``SCHED_IDLE``, and
+``SCHED_EXT`` tasks are scheduled by sched_ext.
+
+However, when the BPF scheduler is loaded and ``SCX_OPS_SWITCH_PARTIAL`` is
+set in ``ops->flags``, only tasks with the ``SCHED_EXT`` policy are scheduled
+by sched_ext, while tasks with ``SCHED_NORMAL``, ``SCHED_BATCH`` and
+``SCHED_IDLE`` policies are scheduled by CFS.
+
+Terminating the sched_ext scheduler program, triggering :kbd:`SysRq-S`, or
+detection of any internal error including stalled runnable tasks aborts the
+BPF scheduler and reverts all tasks back to CFS.
+
+.. code-block:: none
+
+    # make -j16 -C tools/sched_ext
+    # tools/sched_ext/scx_simple
+    local=0 global=3
+    local=5 global=24
+    local=9 global=44
+    local=13 global=56
+    local=17 global=72
+    ^CEXIT: BPF scheduler unregistered
+
+The current status of the BPF scheduler can be determined as follows:
+
+.. code-block:: none
+
+    # cat /sys/kernel/sched_ext/state
+    enabled
+    # cat /sys/kernel/sched_ext/root/ops
+    simple
+
+``tools/sched_ext/scx_show_state.py`` is a drgn script which shows more
+detailed information:
+
+.. code-block:: none
+
+    # tools/sched_ext/scx_show_state.py
+    ops           : simple
+    enabled       : 1
+    switching_all : 1
+    switched_all  : 1
+    enable_state  : enabled (2)
+    bypass_depth  : 0
+    nr_rejected   : 0
+
+If ``CONFIG_SCHED_DEBUG`` is set, whether a given task is on sched_ext can
+be determined as follows:
+
+.. code-block:: none
+
+    # grep ext /proc/self/sched
+    ext.enabled                                  :                    1
+
+The Basics
+==========
+
+Userspace can implement an arbitrary BPF scheduler by loading a set of BPF
+programs that implement ``struct sched_ext_ops``. The only mandatory field
+is ``ops.name`` which must be a valid BPF object name. All operations are
+optional. The following modified excerpt is from
+``tools/sched_ext/scx_simple.bpf.c`` showing a minimal global FIFO scheduler.
+
+.. code-block:: c
+
+    /*
+     * Decide which CPU a task should be migrated to before being
+     * enqueued (either at wakeup, fork time, or exec time). If an
+     * idle core is found by the default ops.select_cpu() implementation,
+     * then dispatch the task directly to SCX_DSQ_LOCAL and skip the
+     * ops.enqueue() callback.
+     *
+     * Note that this implementation has exactly the same behavior as the
+     * default ops.select_cpu implementation. The behavior of the scheduler
+     * would be exactly same if the implementation just didn't define the
+     * simple_select_cpu() struct_ops prog.
+     */
+    s32 BPF_STRUCT_OPS(simple_select_cpu, struct task_struct *p,
+                       s32 prev_cpu, u64 wake_flags)
+    {
+            s32 cpu;
+            /* Need to initialize or the BPF verifier will reject the program */
+            bool direct = false;
+
+            cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, wake_flags, &direct);
+
+            if (direct)
+                    scx_bpf_dispatch(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, 0);
+
+            return cpu;
+    }
+
+    /*
+     * Do a direct dispatch of a task to the global DSQ. This ops.enqueue()
+     * callback will only be invoked if we failed to find a core to dispatch
+     * to in ops.select_cpu() above.
+     *
+     * Note that this implementation has exactly the same behavior as the
+     * default ops.enqueue implementation, which just dispatches the task
+     * to SCX_DSQ_GLOBAL. The behavior of the scheduler would be exactly same
+     * if the implementation just didn't define the simple_enqueue struct_ops
+     * prog.
+     */
+    void BPF_STRUCT_OPS(simple_enqueue, struct task_struct *p, u64 enq_flags)
+    {
+            scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+    }
+
+    s32 BPF_STRUCT_OPS_SLEEPABLE(simple_init)
+    {
+            /*
+             * By default, all SCHED_EXT, SCHED_OTHER, SCHED_IDLE, and
+             * SCHED_BATCH tasks should use sched_ext.
+             */
+            return 0;
+    }
+
+    void BPF_STRUCT_OPS(simple_exit, struct scx_exit_info *ei)
+    {
+            exit_type = ei->type;
+    }
+
+    SEC(".struct_ops")
+    struct sched_ext_ops simple_ops = {
+            .select_cpu             = (void *)simple_select_cpu,
+            .enqueue                = (void *)simple_enqueue,
+            .init                   = (void *)simple_init,
+            .exit                   = (void *)simple_exit,
+            .name                   = "simple",
+    };
+
+Dispatch Queues
+---------------
+
+To match the impedance between the scheduler core and the BPF scheduler,
+sched_ext uses DSQs (dispatch queues) which can operate as both a FIFO and a
+priority queue. By default, there is one global FIFO (``SCX_DSQ_GLOBAL``),
+and one local dsq per CPU (``SCX_DSQ_LOCAL``). The BPF scheduler can manage
+an arbitrary number of dsq's using ``scx_bpf_create_dsq()`` and
+``scx_bpf_destroy_dsq()``.
+
+A CPU always executes a task from its local DSQ. A task is "dispatched" to a
+DSQ. A non-local DSQ is "consumed" to transfer a task to the consuming CPU's
+local DSQ.
+
+When a CPU is looking for the next task to run, if the local DSQ is not
+empty, the first task is picked. Otherwise, the CPU tries to consume the
+global DSQ. If that doesn't yield a runnable task either, ``ops.dispatch()``
+is invoked.
+
+Scheduling Cycle
+----------------
+
+The following briefly shows how a waking task is scheduled and executed.
+
+1. When a task is waking up, ``ops.select_cpu()`` is the first operation
+   invoked. This serves two purposes. First, CPU selection optimization
+   hint. Second, waking up the selected CPU if idle.
+
+   The CPU selected by ``ops.select_cpu()`` is an optimization hint and not
+   binding. The actual decision is made at the last step of scheduling.
+   However, there is a small performance gain if the CPU
+   ``ops.select_cpu()`` returns matches the CPU the task eventually runs on.
+
+   A side-effect of selecting a CPU is waking it up from idle. While a BPF
+   scheduler can wake up any cpu using the ``scx_bpf_kick_cpu()`` helper,
+   using ``ops.select_cpu()`` judiciously can be simpler and more efficient.
+
+   A task can be immediately dispatched to a DSQ from ``ops.select_cpu()`` by
+   calling ``scx_bpf_dispatch()``. If the task is dispatched to
+   ``SCX_DSQ_LOCAL`` from ``ops.select_cpu()``, it will be dispatched to the
+   local DSQ of whichever CPU is returned from ``ops.select_cpu()``.
+   Additionally, dispatching directly from ``ops.select_cpu()`` will cause the
+   ``ops.enqueue()`` callback to be skipped.
+
+   Note that the scheduler core will ignore an invalid CPU selection, for
+   example, if it's outside the allowed cpumask of the task.
+
+2. Once the target CPU is selected, ``ops.enqueue()`` is invoked (unless the
+   task was dispatched directly from ``ops.select_cpu()``). ``ops.enqueue()``
+   can make one of the following decisions:
+
+   * Immediately dispatch the task to either the global or local DSQ by
+     calling ``scx_bpf_dispatch()`` with ``SCX_DSQ_GLOBAL`` or
+     ``SCX_DSQ_LOCAL``, respectively.
+
+   * Immediately dispatch the task to a custom DSQ by calling
+     ``scx_bpf_dispatch()`` with a DSQ ID which is smaller than 2^63.
+
+   * Queue the task on the BPF side.
+
+3. When a CPU is ready to schedule, it first looks at its local DSQ. If
+   empty, it then looks at the global DSQ. If there still isn't a task to
+   run, ``ops.dispatch()`` is invoked which can use the following two
+   functions to populate the local DSQ.
+
+   * ``scx_bpf_dispatch()`` dispatches a task to a DSQ. Any target DSQ can
+     be used - ``SCX_DSQ_LOCAL``, ``SCX_DSQ_LOCAL_ON | cpu``,
+     ``SCX_DSQ_GLOBAL`` or a custom DSQ. While ``scx_bpf_dispatch()``
+     currently can't be called with BPF locks held, this is being worked on
+     and will be supported. ``scx_bpf_dispatch()`` schedules dispatching
+     rather than performing them immediately. There can be up to
+     ``ops.dispatch_max_batch`` pending tasks.
+
+   * ``scx_bpf_consume()`` tranfers a task from the specified non-local DSQ
+     to the dispatching DSQ. This function cannot be called with any BPF
+     locks held. ``scx_bpf_consume()`` flushes the pending dispatched tasks
+     before trying to consume the specified DSQ.
+
+4. After ``ops.dispatch()`` returns, if there are tasks in the local DSQ,
+   the CPU runs the first one. If empty, the following steps are taken:
+
+   * Try to consume the global DSQ. If successful, run the task.
+
+   * If ``ops.dispatch()`` has dispatched any tasks, retry #3.
+
+   * If the previous task is an SCX task and still runnable, keep executing
+     it (see ``SCX_OPS_ENQ_LAST``).
+
+   * Go idle.
+
+Note that the BPF scheduler can always choose to dispatch tasks immediately
+in ``ops.enqueue()`` as illustrated in the above simple example. If only the
+built-in DSQs are used, there is no need to implement ``ops.dispatch()`` as
+a task is never queued on the BPF scheduler and both the local and global
+DSQs are consumed automatically.
+
+``scx_bpf_dispatch()`` queues the task on the FIFO of the target DSQ. Use
+``scx_bpf_dispatch_vtime()`` for the priority queue. Internal DSQs such as
+``SCX_DSQ_LOCAL`` and ``SCX_DSQ_GLOBAL`` do not support priority-queue
+dispatching, and must be dispatched to with ``scx_bpf_dispatch()``.  See the
+function documentation and usage in ``tools/sched_ext/scx_simple.bpf.c`` for
+more information.
+
+Where to Look
+=============
+
+* ``include/linux/sched/ext.h`` defines the core data structures, ops table
+  and constants.
+
+* ``kernel/sched/ext.c`` contains sched_ext core implementation and helpers.
+  The functions prefixed with ``scx_bpf_`` can be called from the BPF
+  scheduler.
+
+* ``tools/sched_ext/`` hosts example BPF scheduler implementations.
+
+  * ``scx_simple[.bpf].c``: Minimal global FIFO scheduler example using a
+    custom DSQ.
+
+  * ``scx_qmap[.bpf].c``: A multi-level FIFO scheduler supporting five
+    levels of priority implemented with ``BPF_MAP_TYPE_QUEUE``.
+
+ABI Instability
+===============
+
+The APIs provided by sched_ext to BPF schedulers programs have no stability
+guarantees. This includes the ops table callbacks and constants defined in
+``include/linux/sched/ext.h``, as well as the ``scx_bpf_`` kfuncs defined in
+``kernel/sched/ext.c``.
+
+While we will attempt to provide a relatively stable API surface when
+possible, they are subject to change without warning between kernel
+versions.
diff --git a/MAINTAINERS b/MAINTAINERS
index 3121709d99e3..bf3b77e96dc4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -19623,6 +19623,19 @@ F:	include/linux/wait.h
 F:	include/uapi/linux/sched.h
 F:	kernel/sched/
 
+SCHEDULER - SCHED_EXT
+R:	Tejun Heo <tj@kernel.org>
+R:	David Vernet <void@manifault.com>
+L:	linux-kernel@vger.kernel.org
+S:	Maintained
+W:	https://github.com/sched-ext/scx
+T:	git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git
+F:	include/linux/sched/ext.h
+F:	kernel/sched/ext.h
+F:	kernel/sched/ext.c
+F:	tools/sched_ext/
+F:	tools/testing/selftests/sched_ext
+
 SCSI LIBSAS SUBSYSTEM
 R:	John Garry <john.g.garry@oracle.com>
 R:	Jason Yan <yanaijie@huawei.com>
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index f7749d0f2562..05bfe4acba1d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -131,6 +131,7 @@
 	*(__dl_sched_class)			\
 	*(__rt_sched_class)			\
 	*(__fair_sched_class)			\
+	*(__ext_sched_class)			\
 	*(__idle_sched_class)			\
 	__sched_class_lowest = .;
 
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 34aaf0e87def..bcebf8096e91 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -29,8 +29,6 @@
 
 struct kernel_clone_args;
 
-#ifdef CONFIG_CGROUPS
-
 /*
  * All weight knobs on the default hierarchy should use the following min,
  * default and max values.  The default value is the logarithmic center of
@@ -40,6 +38,8 @@ struct kernel_clone_args;
 #define CGROUP_WEIGHT_DFL		100
 #define CGROUP_WEIGHT_MAX		10000
 
+#ifdef CONFIG_CGROUPS
+
 enum {
 	CSS_TASK_ITER_PROCS    = (1U << 0),  /* walk only threadgroup leaders */
 	CSS_TASK_ITER_THREADED = (1U << 1),  /* walk all threaded css_sets in the domain */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3c2abbc587b4..dc07eb0d3290 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -80,6 +80,8 @@ struct task_group;
 struct task_struct;
 struct user_event_mm;
 
+#include <linux/sched/ext.h>
+
 /*
  * Task state bitmask. NOTE! These bits are also
  * encoded in fs/proc/array.c: get_task_state().
@@ -798,6 +800,9 @@ struct task_struct {
 	struct sched_rt_entity		rt;
 	struct sched_dl_entity		dl;
 	struct sched_dl_entity		*dl_server;
+#ifdef CONFIG_SCHED_CLASS_EXT
+	struct sched_ext_entity		scx;
+#endif
 	const struct sched_class	*sched_class;
 
 #ifdef CONFIG_SCHED_CORE
diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
new file mode 100644
index 000000000000..593d2f4909dd
--- /dev/null
+++ b/include/linux/sched/ext.h
@@ -0,0 +1,206 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#ifndef _LINUX_SCHED_EXT_H
+#define _LINUX_SCHED_EXT_H
+
+#ifdef CONFIG_SCHED_CLASS_EXT
+
+#include <linux/llist.h>
+#include <linux/rhashtable-types.h>
+
+enum scx_public_consts {
+	SCX_OPS_NAME_LEN	= 128,
+
+	SCX_SLICE_DFL		= 20 * 1000000,	/* 20ms */
+	SCX_SLICE_INF		= U64_MAX,	/* infinite, implies nohz */
+};
+
+/*
+ * DSQ (dispatch queue) IDs are 64bit of the format:
+ *
+ *   Bits: [63] [62 ..  0]
+ *         [ B] [   ID   ]
+ *
+ *    B: 1 for IDs for built-in DSQs, 0 for ops-created user DSQs
+ *   ID: 63 bit ID
+ *
+ * Built-in IDs:
+ *
+ *   Bits: [63] [62] [61..32] [31 ..  0]
+ *         [ 1] [ L] [   R  ] [    V   ]
+ *
+ *    1: 1 for built-in DSQs.
+ *    L: 1 for LOCAL_ON DSQ IDs, 0 for others
+ *    V: For LOCAL_ON DSQ IDs, a CPU number. For others, a pre-defined value.
+ */
+enum scx_dsq_id_flags {
+	SCX_DSQ_FLAG_BUILTIN	= 1LLU << 63,
+	SCX_DSQ_FLAG_LOCAL_ON	= 1LLU << 62,
+
+	SCX_DSQ_INVALID		= SCX_DSQ_FLAG_BUILTIN | 0,
+	SCX_DSQ_GLOBAL		= SCX_DSQ_FLAG_BUILTIN | 1,
+	SCX_DSQ_LOCAL		= SCX_DSQ_FLAG_BUILTIN | 2,
+	SCX_DSQ_LOCAL_ON	= SCX_DSQ_FLAG_BUILTIN | SCX_DSQ_FLAG_LOCAL_ON,
+	SCX_DSQ_LOCAL_CPU_MASK	= 0xffffffffLLU,
+};
+
+/*
+ * A dispatch queue (DSQ) can be either a FIFO or p->scx.dsq_vtime ordered
+ * queue. A built-in DSQ is always a FIFO. The built-in local DSQs are used to
+ * buffer between the scheduler core and the BPF scheduler. See the
+ * documentation for more details.
+ */
+struct scx_dispatch_q {
+	raw_spinlock_t		lock;
+	struct list_head	list;	/* tasks in dispatch order */
+	struct rb_root		priq;	/* used to order by p->scx.dsq_vtime */
+	u32			nr;
+	u32			seq;	/* used by BPF iter */
+	u64			id;
+	struct rhash_head	hash_node;
+	struct llist_node	free_node;
+	struct rcu_head		rcu;
+};
+
+/* scx_entity.flags */
+enum scx_ent_flags {
+	SCX_TASK_QUEUED		= 1 << 0, /* on ext runqueue */
+	SCX_TASK_BAL_KEEP	= 1 << 1, /* balance decided to keep current */
+	SCX_TASK_RESET_RUNNABLE_AT = 1 << 2, /* runnable_at should be reset */
+	SCX_TASK_DEQD_FOR_SLEEP	= 1 << 3, /* last dequeue was for SLEEP */
+
+	SCX_TASK_STATE_SHIFT	= 8,	  /* bit 8 and 9 are used to carry scx_task_state */
+	SCX_TASK_STATE_BITS	= 2,
+	SCX_TASK_STATE_MASK	= ((1 << SCX_TASK_STATE_BITS) - 1) << SCX_TASK_STATE_SHIFT,
+
+	SCX_TASK_CURSOR		= 1 << 31, /* iteration cursor, not a task */
+};
+
+/* scx_entity.flags & SCX_TASK_STATE_MASK */
+enum scx_task_state {
+	SCX_TASK_NONE,		/* ops.init_task() not called yet */
+	SCX_TASK_INIT,		/* ops.init_task() succeeded, but task can be cancelled */
+	SCX_TASK_READY,		/* fully initialized, but not in sched_ext */
+	SCX_TASK_ENABLED,	/* fully initialized and in sched_ext */
+
+	SCX_TASK_NR_STATES,
+};
+
+/* scx_entity.dsq_flags */
+enum scx_ent_dsq_flags {
+	SCX_TASK_DSQ_ON_PRIQ	= 1 << 0, /* task is queued on the priority queue of a dsq */
+};
+
+/*
+ * Mask bits for scx_entity.kf_mask. Not all kfuncs can be called from
+ * everywhere and the following bits track which kfunc sets are currently
+ * allowed for %current. This simple per-task tracking works because SCX ops
+ * nest in a limited way. BPF will likely implement a way to allow and disallow
+ * kfuncs depending on the calling context which will replace this manual
+ * mechanism. See scx_kf_allow().
+ */
+enum scx_kf_mask {
+	SCX_KF_UNLOCKED		= 0,	  /* not sleepable, not rq locked */
+	/* all non-sleepables may be nested inside SLEEPABLE */
+	SCX_KF_SLEEPABLE	= 1 << 0, /* sleepable init operations */
+	/* ENQUEUE and DISPATCH may be nested inside CPU_RELEASE */
+	SCX_KF_CPU_RELEASE	= 1 << 1, /* ops.cpu_release() */
+	/* ops.dequeue (in REST) may be nested inside DISPATCH */
+	SCX_KF_DISPATCH		= 1 << 2, /* ops.dispatch() */
+	SCX_KF_ENQUEUE		= 1 << 3, /* ops.enqueue() and ops.select_cpu() */
+	SCX_KF_SELECT_CPU	= 1 << 4, /* ops.select_cpu() */
+	SCX_KF_REST		= 1 << 5, /* other rq-locked operations */
+
+	__SCX_KF_RQ_LOCKED	= SCX_KF_CPU_RELEASE | SCX_KF_DISPATCH |
+				  SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU | SCX_KF_REST,
+	__SCX_KF_TERMINAL	= SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU | SCX_KF_REST,
+};
+
+struct scx_dsq_list_node {
+	struct list_head	node;
+	bool			is_bpf_iter_cursor;
+};
+
+/*
+ * The following is embedded in task_struct and contains all fields necessary
+ * for a task to be scheduled by SCX.
+ */
+struct sched_ext_entity {
+	struct scx_dispatch_q	*dsq;
+	struct scx_dsq_list_node dsq_list;	/* dispatch order */
+	struct rb_node		dsq_priq;	/* p->scx.dsq_vtime order */
+	u32			dsq_seq;
+	u32			dsq_flags;	/* protected by DSQ lock */
+	u32			flags;		/* protected by rq lock */
+	u32			weight;
+	s32			sticky_cpu;
+	s32			holding_cpu;
+	u32			kf_mask;	/* see scx_kf_mask above */
+	struct task_struct	*kf_tasks[2];	/* see SCX_CALL_OP_TASK() */
+	atomic_long_t		ops_state;
+
+	struct list_head	runnable_node;	/* rq->scx.runnable_list */
+	unsigned long		runnable_at;
+
+#ifdef CONFIG_SCHED_CORE
+	u64			core_sched_at;	/* see scx_prio_less() */
+#endif
+	u64			ddsp_dsq_id;
+	u64			ddsp_enq_flags;
+
+	/* BPF scheduler modifiable fields */
+
+	/*
+	 * Runtime budget in nsecs. This is usually set through
+	 * scx_bpf_dispatch() but can also be modified directly by the BPF
+	 * scheduler. Automatically decreased by SCX as the task executes. On
+	 * depletion, a scheduling event is triggered.
+	 *
+	 * This value is cleared to zero if the task is preempted by
+	 * %SCX_KICK_PREEMPT and shouldn't be used to determine how long the
+	 * task ran. Use p->se.sum_exec_runtime instead.
+	 */
+	u64			slice;
+
+	/*
+	 * Used to order tasks when dispatching to the vtime-ordered priority
+	 * queue of a dsq. This is usually set through scx_bpf_dispatch_vtime()
+	 * but can also be modified directly by the BPF scheduler. Modifying it
+	 * while a task is queued on a dsq may mangle the ordering and is not
+	 * recommended.
+	 */
+	u64			dsq_vtime;
+
+	/*
+	 * If set, reject future sched_setscheduler(2) calls updating the policy
+	 * to %SCHED_EXT with -%EACCES.
+	 *
+	 * If set from ops.init_task() and the task's policy is already
+	 * %SCHED_EXT, which can happen while the BPF scheduler is being loaded
+	 * or by inhering the parent's policy during fork, the task's policy is
+	 * rejected and forcefully reverted to %SCHED_NORMAL. The number of
+	 * such events are reported through /sys/kernel/debug/sched_ext::nr_rejected.
+	 */
+	bool			disallow;	/* reject switching into SCX */
+
+	/* cold fields */
+	/* must be the last field, see init_scx_entity() */
+	struct list_head	tasks_node;
+};
+
+void sched_ext_free(struct task_struct *p);
+void print_scx_info(const char *log_lvl, struct task_struct *p);
+
+#else	/* !CONFIG_SCHED_CLASS_EXT */
+
+static inline void sched_ext_free(struct task_struct *p) {}
+static inline void print_scx_info(const char *log_lvl, struct task_struct *p) {}
+
+#endif	/* CONFIG_SCHED_CLASS_EXT */
+#endif	/* _LINUX_SCHED_EXT_H */
diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index d362aacf9f89..4df2f9055587 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -63,7 +63,8 @@ extern asmlinkage void schedule_tail(struct task_struct *prev);
 extern void init_idle(struct task_struct *idle, int cpu);
 
 extern int sched_fork(unsigned long clone_flags, struct task_struct *p);
-extern void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs);
+extern int sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs);
+extern void sched_cancel_fork(struct task_struct *p);
 extern void sched_post_fork(struct task_struct *p);
 extern void sched_dead(struct task_struct *p);
 
diff --git a/include/trace/events/sched_ext.h b/include/trace/events/sched_ext.h
new file mode 100644
index 000000000000..fe19da7315a9
--- /dev/null
+++ b/include/trace/events/sched_ext.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM sched_ext
+
+#if !defined(_TRACE_SCHED_EXT_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SCHED_EXT_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(sched_ext_dump,
+
+	TP_PROTO(const char *line),
+
+	TP_ARGS(line),
+
+	TP_STRUCT__entry(
+		__string(line, line)
+	),
+
+	TP_fast_assign(
+		__assign_str(line, line);
+	),
+
+	TP_printk("%s",
+		__get_str(line)
+	)
+);
+
+#endif /* _TRACE_SCHED_EXT_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 3bac0a8ceab2..359a14cc76a4 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -118,6 +118,7 @@ struct clone_args {
 /* SCHED_ISO: reserved but not implemented yet */
 #define SCHED_IDLE		5
 #define SCHED_DEADLINE		6
+#define SCHED_EXT		7
 
 /* Can be ORed in to make sure the process is reverted back to SCHED_NORMAL on fork */
 #define SCHED_RESET_ON_FORK     0x40000000
diff --git a/init/init_task.c b/init/init_task.c
index 4daee6d761c8..ce882dbd2635 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -6,6 +6,7 @@
 #include <linux/sched/sysctl.h>
 #include <linux/sched/rt.h>
 #include <linux/sched/task.h>
+#include <linux/sched/ext.h>
 #include <linux/init.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
@@ -97,6 +98,17 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
 #endif
 #ifdef CONFIG_CGROUP_SCHED
 	.sched_task_group = &root_task_group,
+#endif
+#ifdef CONFIG_SCHED_CLASS_EXT
+	.scx		= {
+		.dsq_list.node	= LIST_HEAD_INIT(init_task.scx.dsq_list.node),
+		.sticky_cpu	= -1,
+		.holding_cpu	= -1,
+		.runnable_node	= LIST_HEAD_INIT(init_task.scx.runnable_node),
+		.runnable_at	= INITIAL_JIFFIES,
+		.ddsp_dsq_id	= SCX_DSQ_INVALID,
+		.slice		= SCX_SLICE_DFL,
+	},
 #endif
 	.ptraced	= LIST_HEAD_INIT(init_task.ptraced),
 	.ptrace_entry	= LIST_HEAD_INIT(init_task.ptrace_entry),
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index c2f1fd95a821..f3d140c3acc1 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -133,4 +133,28 @@ config SCHED_CORE
 	  which is the likely usage by Linux distributions, there should
 	  be no measurable impact on performance.
 
-
+config SCHED_CLASS_EXT
+	bool "Extensible Scheduling Class"
+	depends on BPF_SYSCALL && BPF_JIT && DEBUG_INFO_BTF
+	help
+	  This option enables a new scheduler class sched_ext (SCX), which
+	  allows scheduling policies to be implemented as BPF programs to
+	  achieve the following:
+
+	  - Ease of experimentation and exploration: Enabling rapid
+	    iteration of new scheduling policies.
+	  - Customization: Building application-specific schedulers which
+	    implement policies that are not applicable to general-purpose
+	    schedulers.
+	  - Rapid scheduler deployments: Non-disruptive swap outs of
+	    scheduling policies in production environments.
+
+	  sched_ext leverages BPF struct_ops feature to define a structure
+	  which exports function callbacks and flags to BPF programs that
+	  wish to implement scheduling policies. The struct_ops structure
+	  exported by sched_ext is struct sched_ext_ops, and is conceptually
+	  similar to struct sched_class.
+
+	  For more information:
+	    Documentation/scheduler/sched-ext.rst
+	    https://github.com/sched-ext/scx
diff --git a/kernel/fork.c b/kernel/fork.c
index aebb3e6c96dc..5d1f9de254d6 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -23,6 +23,7 @@
 #include <linux/sched/task.h>
 #include <linux/sched/task_stack.h>
 #include <linux/sched/cputime.h>
+#include <linux/sched/ext.h>
 #include <linux/seq_file.h>
 #include <linux/rtmutex.h>
 #include <linux/init.h>
@@ -971,6 +972,7 @@ void __put_task_struct(struct task_struct *tsk)
 	WARN_ON(refcount_read(&tsk->usage));
 	WARN_ON(tsk == current);
 
+	sched_ext_free(tsk);
 	io_uring_free(tsk);
 	cgroup_free(tsk);
 	task_numa_free(tsk, true);
@@ -2363,7 +2365,7 @@ __latent_entropy struct task_struct *copy_process(
 
 	retval = perf_event_init_task(p, clone_flags);
 	if (retval)
-		goto bad_fork_cleanup_policy;
+		goto bad_fork_sched_cancel_fork;
 	retval = audit_alloc(p);
 	if (retval)
 		goto bad_fork_cleanup_perf;
@@ -2496,7 +2498,9 @@ __latent_entropy struct task_struct *copy_process(
 	 * cgroup specific, it unconditionally needs to place the task on a
 	 * runqueue.
 	 */
-	sched_cgroup_fork(p, args);
+	retval = sched_cgroup_fork(p, args);
+	if (retval)
+		goto bad_fork_cancel_cgroup;
 
 	/*
 	 * From this point on we must avoid any synchronous user-space
@@ -2542,13 +2546,13 @@ __latent_entropy struct task_struct *copy_process(
 	/* Don't start children in a dying pid namespace */
 	if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
 		retval = -ENOMEM;
-		goto bad_fork_cancel_cgroup;
+		goto bad_fork_core_free;
 	}
 
 	/* Let kill terminate clone/fork in the middle */
 	if (fatal_signal_pending(current)) {
 		retval = -EINTR;
-		goto bad_fork_cancel_cgroup;
+		goto bad_fork_core_free;
 	}
 
 	/* No more failure paths after this point. */
@@ -2622,10 +2626,11 @@ __latent_entropy struct task_struct *copy_process(
 
 	return p;
 
-bad_fork_cancel_cgroup:
+bad_fork_core_free:
 	sched_core_free(p);
 	spin_unlock(&current->sighand->siglock);
 	write_unlock_irq(&tasklist_lock);
+bad_fork_cancel_cgroup:
 	cgroup_cancel_fork(p, args);
 bad_fork_put_pidfd:
 	if (clone_flags & CLONE_PIDFD) {
@@ -2664,6 +2669,8 @@ __latent_entropy struct task_struct *copy_process(
 	audit_free(p);
 bad_fork_cleanup_perf:
 	perf_event_free_task(p);
+bad_fork_sched_cancel_fork:
+	sched_cancel_fork(p);
 bad_fork_cleanup_policy:
 	lockdep_free_task(p);
 #ifdef CONFIG_NUMA
diff --git a/kernel/sched/build_policy.c b/kernel/sched/build_policy.c
index d9dc9ab3773f..e7d539bb721e 100644
--- a/kernel/sched/build_policy.c
+++ b/kernel/sched/build_policy.c
@@ -16,18 +16,25 @@
 #include <linux/sched/clock.h>
 #include <linux/sched/cputime.h>
 #include <linux/sched/hotplug.h>
+#include <linux/sched/isolation.h>
 #include <linux/sched/posix-timers.h>
 #include <linux/sched/rt.h>
 
 #include <linux/cpuidle.h>
 #include <linux/jiffies.h>
+#include <linux/kobject.h>
 #include <linux/livepatch.h>
+#include <linux/pm.h>
 #include <linux/psi.h>
+#include <linux/rhashtable.h>
+#include <linux/seq_buf.h>
 #include <linux/seqlock_api.h>
 #include <linux/slab.h>
 #include <linux/suspend.h>
 #include <linux/tsacct_kern.h>
 #include <linux/vtime.h>
+#include <linux/sysrq.h>
+#include <linux/percpu-rwsem.h>
 
 #include <uapi/linux/sched/types.h>
 
@@ -52,3 +59,6 @@
 #include "cputime.c"
 #include "deadline.c"
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+# include "ext.c"
+#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d211d40a2edc..e5a6766b3a45 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -168,7 +168,10 @@ static inline int __task_prio(const struct task_struct *p)
 	if (p->sched_class == &idle_sched_class)
 		return MAX_RT_PRIO + NICE_WIDTH; /* 140 */
 
-	return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
+	if (task_on_scx(p))
+		return MAX_RT_PRIO + MAX_NICE + 1; /* 120, squash ext */
+
+	return MAX_RT_PRIO + MAX_NICE; /* 119, squash fair */
 }
 
 /*
@@ -197,6 +200,11 @@ static inline bool prio_less(const struct task_struct *a,
 	if (pa == MAX_RT_PRIO + MAX_NICE)	/* fair */
 		return cfs_prio_less(a, b, in_fi);
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+	if (pa == MAX_RT_PRIO + MAX_NICE + 1)	/* ext */
+		return scx_prio_less(a, b, in_fi);
+#endif
+
 	return false;
 }
 
@@ -1255,11 +1263,14 @@ bool sched_can_stop_tick(struct rq *rq)
 		return true;
 
 	/*
-	 * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left;
-	 * if there's more than one we need the tick for involuntary
-	 * preemption.
+	 * If there are no DL,RR/FIFO tasks, there must only be CFS or SCX tasks
+	 * left. For CFS, if there's more than one we need the tick for
+	 * involuntary preemption. For SCX, ask.
 	 */
-	if (rq->nr_running > 1)
+	if (!scx_switched_all() && rq->nr_running > 1)
+		return false;
+
+	if (scx_enabled() && !scx_can_stop_tick(rq))
 		return false;
 
 	/*
@@ -1327,27 +1338,24 @@ int tg_nop(struct task_group *tg, void *data)
 static void set_load_weight(struct task_struct *p, bool update_load)
 {
 	int prio = p->static_prio - MAX_RT_PRIO;
-	struct load_weight *load = &p->se.load;
+	struct load_weight lw;
 
-	/*
-	 * SCHED_IDLE tasks get minimal weight:
-	 */
 	if (task_has_idle_policy(p)) {
-		load->weight = scale_load(WEIGHT_IDLEPRIO);
-		load->inv_weight = WMULT_IDLEPRIO;
-		return;
+		lw.weight = scale_load(WEIGHT_IDLEPRIO);
+		lw.inv_weight = WMULT_IDLEPRIO;
+	} else {
+		lw.weight = scale_load(sched_prio_to_weight[prio]);
+		lw.inv_weight = sched_prio_to_wmult[prio];
 	}
 
 	/*
 	 * SCHED_OTHER tasks have to update their load when changing their
 	 * weight
 	 */
-	if (update_load && p->sched_class == &fair_sched_class) {
-		reweight_task(p, prio);
-	} else {
-		load->weight = scale_load(sched_prio_to_weight[prio]);
-		load->inv_weight = sched_prio_to_wmult[prio];
-	}
+	if (update_load && p->sched_class->reweight_task)
+		p->sched_class->reweight_task(task_rq(p), p, &lw);
+	else
+		p->se.load = lw;
 }
 
 #ifdef CONFIG_UCLAMP_TASK
@@ -2214,6 +2222,17 @@ inline int task_curr(const struct task_struct *p)
 	return cpu_curr(task_cpu(p)) == p;
 }
 
+/*
+ * ->switching_to() is called with the pi_lock and rq_lock held and must not
+ * mess with locking.
+ */
+void check_class_changing(struct rq *rq, struct task_struct *p,
+			  const struct sched_class *prev_class)
+{
+	if (prev_class != p->sched_class && p->sched_class->switching_to)
+		p->sched_class->switching_to(rq, p);
+}
+
 /*
  * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
  * use the balance_callback list if you want balancing.
@@ -2221,9 +2240,9 @@ inline int task_curr(const struct task_struct *p)
  * this means any call to check_class_changed() must be followed by a call to
  * balance_callback().
  */
-static inline void check_class_changed(struct rq *rq, struct task_struct *p,
-				       const struct sched_class *prev_class,
-				       int oldprio)
+void check_class_changed(struct rq *rq, struct task_struct *p,
+			 const struct sched_class *prev_class,
+			 int oldprio)
 {
 	if (prev_class != p->sched_class) {
 		if (prev_class->switched_from)
@@ -3986,6 +4005,15 @@ bool cpus_share_resources(int this_cpu, int that_cpu)
 
 static inline bool ttwu_queue_cond(struct task_struct *p, int cpu)
 {
+	/*
+	 * The BPF scheduler may depend on select_task_rq() being invoked during
+	 * wakeups. In addition, @p may end up executing on a different CPU
+	 * regardless of what happens in the wakeup path making the ttwu_queue
+	 * optimization less meaningful. Skip if on SCX.
+	 */
+	if (task_on_scx(p))
+		return false;
+
 	/*
 	 * Do not complicate things with the async wake_list while the CPU is
 	 * in hotplug state.
@@ -4553,6 +4581,10 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
 	p->rt.on_rq		= 0;
 	p->rt.on_list		= 0;
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+	init_scx_entity(&p->scx);
+#endif
+
 #ifdef CONFIG_PREEMPT_NOTIFIERS
 	INIT_HLIST_HEAD(&p->preempt_notifiers);
 #endif
@@ -4794,10 +4826,18 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 
 	if (dl_prio(p->prio))
 		return -EAGAIN;
-	else if (rt_prio(p->prio))
+
+	scx_pre_fork(p);
+
+	if (rt_prio(p->prio)) {
 		p->sched_class = &rt_sched_class;
-	else
+#ifdef CONFIG_SCHED_CLASS_EXT
+	} else if (task_should_scx(p)) {
+		p->sched_class = &ext_sched_class;
+#endif
+	} else {
 		p->sched_class = &fair_sched_class;
+	}
 
 	init_entity_runnable_average(&p->se);
 
@@ -4817,7 +4857,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 	return 0;
 }
 
-void sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
+int sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)
 {
 	unsigned long flags;
 
@@ -4979,6 +4979,13 @@
 	if (p->sched_class->task_fork)
 		p->sched_class->task_fork(p);
 	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+
+	return scx_fork(p);
+}
+
+void sched_cancel_fork(struct task_struct *p)
+{
+	scx_cancel_fork(p);
 }
 
 void sched_post_fork(struct task_struct *p)
@@ -4987,6 +4994,7 @@
 	sched_post_fork_bore(p);
 #endif // CONFIG_SCHED_BORE
 	uclamp_post_fork(p);
+	scx_post_fork(p);
 }
 
 unsigned long to_ratio(u64 period, u64 runtime)
@@ -5687,6 +5735,7 @@ void scheduler_tick(void)
 	calc_global_load_tick(rq);
 	sched_core_tick(rq);
 	task_tick_mm_cid(rq, curr);
+	scx_tick(rq);
 
 	rq_unlock(rq, &rf);
 
@@ -5699,8 +5748,10 @@ void scheduler_tick(void)
 		wq_worker_tick(curr);
 
 #ifdef CONFIG_SMP
-	rq->idle_balance = idle_cpu(cpu);
-	trigger_load_balance(rq);
+	if (!scx_switched_all()) {
+		rq->idle_balance = idle_cpu(cpu);
+		trigger_load_balance(rq);
+	}
 #endif
 }
 
@@ -5991,7 +6042,19 @@ static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
 				  struct rq_flags *rf)
 {
 #ifdef CONFIG_SMP
+	const struct sched_class *start_class = prev->sched_class;
 	const struct sched_class *class;
+
+#ifdef CONFIG_SCHED_CLASS_EXT
+	/*
+	 * SCX requires a balance() call before every pick_next_task() including
+	 * when waking up from SCHED_IDLE. If @start_class is below SCX, start
+	 * from SCX instead.
+	 */
+	if (sched_class_above(&ext_sched_class, start_class))
+		start_class = &ext_sched_class;
+#endif
+
 	/*
 	 * We must do the balancing pass before put_prev_task(), such
 	 * that when we release the rq->lock the task is in the same
@@ -6000,7 +6063,7 @@ static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
 	 * We can terminate the balance pass as soon as we know there is
 	 * a runnable task of @class priority or higher.
 	 */
-	for_class_range(class, prev->sched_class, &idle_sched_class) {
+	for_active_class_range(class, start_class, &idle_sched_class) {
 		if (class->balance(rq, prev, rf))
 			break;
 	}
@@ -6018,6 +6081,9 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	const struct sched_class *class;
 	struct task_struct *p;
 
+	if (scx_enabled())
+		goto restart;
+
 	/*
 	 * Optimization: we know that if all tasks are in the fair class we can
 	 * call that function directly, but only if the @prev task wasn't of a
@@ -6058,10 +6124,15 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 	if (prev->dl_server)
 		prev->dl_server = NULL;
 
-	for_each_class(class) {
+	for_each_active_class(class) {
 		p = class->pick_next_task(rq);
-		if (p)
+		if (p) {
+			const struct sched_class *prev_class = prev->sched_class;
+
+			if (class != prev_class && prev_class->switch_class)
+				prev_class->switch_class(rq, p);
 			return p;
+		}
 	}
 
 	BUG(); /* The idle class should always have a runnable task. */
@@ -6091,7 +6162,7 @@ static inline struct task_struct *pick_task(struct rq *rq)
 	const struct sched_class *class;
 	struct task_struct *p;
 
-	for_each_class(class) {
+	for_each_active_class(class) {
 		p = class->pick_task(rq);
 		if (p)
 			return p;
@@ -7081,12 +7152,16 @@ int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flag
 }
 EXPORT_SYMBOL(default_wake_function);
 
-static void __setscheduler_prio(struct task_struct *p, int prio)
+void __setscheduler_prio(struct task_struct *p, int prio)
 {
 	if (dl_prio(prio))
 		p->sched_class = &dl_sched_class;
 	else if (rt_prio(prio))
 		p->sched_class = &rt_sched_class;
+#ifdef CONFIG_SCHED_CLASS_EXT
+	else if (task_should_scx(p))
+		p->sched_class = &ext_sched_class;
+#endif
 	else
 		p->sched_class = &fair_sched_class;
 
@@ -7247,6 +7322,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
 	}
 
 	__setscheduler_prio(p, prio);
+	check_class_changing(rq, p, prev_class);
 
 	if (queued)
 		enqueue_task(rq, p, queue_flag);
@@ -7468,6 +7544,25 @@ int sched_core_idle_cpu(int cpu)
 #endif
 
 #ifdef CONFIG_SMP
+/*
+ * Load avg and utiliztion metrics need to be updated periodically and before
+ * consumption. This function updates the metrics for all subsystems except for
+ * the fair class. @rq must be locked and have its clock updated.
+ */
+bool update_other_load_avgs(struct rq *rq)
+{
+	u64 now = rq_clock_pelt(rq);
+	const struct sched_class *curr_class = rq->curr->sched_class;
+	unsigned long hw_pressure = arch_scale_thermal_pressure(cpu_of(rq));
+
+	lockdep_assert_rq_held(rq);
+
+	return update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
+		update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
+		update_thermal_load_avg(now, rq, hw_pressure) |
+		update_irq_load_avg(rq, 0);
+}
+
 /*
  * This function computes an effective utilization for the given CPU, to be
  * used for frequency selection given the linear relation: f = u * f_max.
@@ -7790,6 +7885,10 @@ static int __sched_setscheduler(struct task_struct *p,
 		goto unlock;
 	}
 
+	retval = scx_check_setscheduler(p, policy);
+	if (retval)
+		goto unlock;
+
 	/*
 	 * If not changing anything there's no need to proceed further,
 	 * but store a possible modification of reset_on_fork.
@@ -7892,6 +7991,7 @@ static int __sched_setscheduler(struct task_struct *p,
 		__setscheduler_prio(p, newprio);
 	}
 	__setscheduler_uclamp(p, attr);
+	check_class_changing(rq, p, prev_class);
 
 	if (queued) {
 		/*
@@ -9067,6 +9167,7 @@ SYSCALL_DEFINE1(sched_get_priority_max, int, policy)
 	case SCHED_NORMAL:
 	case SCHED_BATCH:
 	case SCHED_IDLE:
+	case SCHED_EXT:
 		ret = 0;
 		break;
 	}
@@ -9094,6 +9195,7 @@ SYSCALL_DEFINE1(sched_get_priority_min, int, policy)
 	case SCHED_NORMAL:
 	case SCHED_BATCH:
 	case SCHED_IDLE:
+	case SCHED_EXT:
 		ret = 0;
 	}
 	return ret;
@@ -9189,6 +9291,7 @@ void sched_show_task(struct task_struct *p)
 
 	print_worker_info(KERN_INFO, p);
 	print_stop_info(KERN_INFO, p);
+	print_scx_info(KERN_INFO, p);
 	show_stack(p, NULL, KERN_INFO);
 	put_task_stack(p);
 }
@@ -9681,6 +9784,8 @@ int sched_cpu_activate(unsigned int cpu)
 		cpuset_cpu_active();
 	}
 
+	scx_rq_activate(rq);
+
 	/*
 	 * Put the rq online, if not already. This happens:
 	 *
@@ -9741,6 +9846,8 @@ int sched_cpu_deactivate(unsigned int cpu)
 	}
 	rq_unlock_irqrestore(rq, &rf);
 
+	scx_rq_deactivate(rq);
+
 #ifdef CONFIG_SCHED_SMT
 	/*
 	 * When going down, decrement the number of cores with SMT present.
@@ -10062,11 +10062,15 @@
 	int i;
 
 	/* Make sure the linker didn't screw up */
-	BUG_ON(&idle_sched_class != &fair_sched_class + 1 ||
-	       &fair_sched_class != &rt_sched_class + 1 ||
-	       &rt_sched_class   != &dl_sched_class + 1);
 #ifdef CONFIG_SMP
-	BUG_ON(&dl_sched_class != &stop_sched_class + 1);
+	BUG_ON(!sched_class_above(&stop_sched_class, &dl_sched_class));
+#endif
+	BUG_ON(!sched_class_above(&dl_sched_class, &rt_sched_class));
+	BUG_ON(!sched_class_above(&rt_sched_class, &fair_sched_class));
+	BUG_ON(!sched_class_above(&fair_sched_class, &idle_sched_class));
+#ifdef CONFIG_SCHED_CLASS_EXT
+	BUG_ON(!sched_class_above(&fair_sched_class, &ext_sched_class));
+	BUG_ON(!sched_class_above(&ext_sched_class, &idle_sched_class));
 #endif
 
 #ifdef CONFIG_SCHED_BORE
@@ -10097,6 +10208,7 @@ void __init sched_init(void)
 	balance_push_set(smp_processor_id(), false);
 #endif
 	init_sched_fair_class();
+	init_sched_ext_class();
 
 	psi_init();
 
@@ -10523,11 +10635,6 @@ void sched_move_task(struct task_struct *tsk)
 	}
 }
 
-static inline struct task_group *css_tg(struct cgroup_subsys_state *css)
-{
-	return css ? container_of(css, struct task_group, css) : NULL;
-}
-
 static struct cgroup_subsys_state *
 cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 {
@@ -11294,29 +11401,27 @@ static int cpu_local_stat_show(struct seq_file *sf,
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
+
+static unsigned long tg_weight(struct task_group *tg)
+{
+	return scale_load_down(tg->shares);
+}
+
 static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
 			       struct cftype *cft)
 {
-	struct task_group *tg = css_tg(css);
-	u64 weight = scale_load_down(tg->shares);
-
-	return DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024);
+	return sched_weight_to_cgroup(tg_weight(css_tg(css)));
 }
 
 static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
-				struct cftype *cft, u64 weight)
+				struct cftype *cft, u64 cgrp_weight)
 {
-	/*
-	 * cgroup weight knobs should use the common MIN, DFL and MAX
-	 * values which are 1, 100 and 10000 respectively.  While it loses
-	 * a bit of range on both ends, it maps pretty well onto the shares
-	 * value used by scheduler and the round-trip conversions preserve
-	 * the original value over the entire range.
-	 */
-	if (weight < CGROUP_WEIGHT_MIN || weight > CGROUP_WEIGHT_MAX)
+	unsigned long weight;
+
+	if (cgrp_weight < CGROUP_WEIGHT_MIN || cgrp_weight > CGROUP_WEIGHT_MAX)
 		return -ERANGE;
 
-	weight = DIV_ROUND_CLOSEST_ULL(weight * 1024, CGROUP_WEIGHT_DFL);
+	weight = sched_weight_from_cgroup(cgrp_weight);
 
 	return sched_group_set_shares(css_tg(css), scale_load(weight));
 }
@@ -11324,7 +11429,7 @@ static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
 static s64 cpu_weight_nice_read_s64(struct cgroup_subsys_state *css,
 				    struct cftype *cft)
 {
-	unsigned long weight = scale_load_down(css_tg(css)->shares);
+	unsigned long weight = tg_weight(css_tg(css));
 	int last_delta = INT_MAX;
 	int prio, delta;
 
@@ -12065,3 +12170,38 @@ void sched_mm_cid_fork(struct task_struct *t)
 	t->mm_cid_active = 1;
 }
 #endif
+
+#ifdef CONFIG_SCHED_CLASS_EXT
+void sched_deq_and_put_task(struct task_struct *p, int queue_flags,
+			    struct sched_enq_and_set_ctx *ctx)
+{
+	struct rq *rq = task_rq(p);
+
+	lockdep_assert_rq_held(rq);
+
+	*ctx = (struct sched_enq_and_set_ctx){
+		.p = p,
+		.queue_flags = queue_flags,
+		.queued = task_on_rq_queued(p),
+		.running = task_current(rq, p),
+	};
+
+	update_rq_clock(rq);
+	if (ctx->queued)
+		dequeue_task(rq, p, queue_flags | DEQUEUE_NOCLOCK);
+	if (ctx->running)
+		put_prev_task(rq, p);
+}
+
+void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx)
+{
+	struct rq *rq = task_rq(ctx->p);
+
+	lockdep_assert_rq_held(rq);
+
+	if (ctx->queued)
+		enqueue_task(rq, ctx->p, ctx->queue_flags | ENQUEUE_NOCLOCK);
+	if (ctx->running)
+		set_next_task(rq, ctx->p);
+}
+#endif	/* CONFIG_SCHED_CLASS_EXT */
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index eece6244f9d2..e683e5d08daa 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -197,8 +197,10 @@ unsigned long sugov_effective_cpu_perf(int cpu, unsigned long actual,
 
 static void sugov_get_util(struct sugov_cpu *sg_cpu, unsigned long boost)
 {
-	unsigned long min, max, util = cpu_util_cfs_boost(sg_cpu->cpu);
+	unsigned long min, max, util = scx_cpuperf_target(sg_cpu->cpu);
 
+	if (!scx_switched_all())
+		util += cpu_util_cfs_boost(sg_cpu->cpu);
 	util = effective_cpu_util(sg_cpu->cpu, util, &min, &max);
 	util = max(util, boost);
 	sg_cpu->bw_min = min;
@@ -325,16 +327,35 @@ static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
 }
 
 #ifdef CONFIG_NO_HZ_COMMON
-static bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu)
+static bool sugov_hold_freq(struct sugov_cpu *sg_cpu)
 {
-	unsigned long idle_calls = tick_nohz_get_idle_calls_cpu(sg_cpu->cpu);
-	bool ret = idle_calls == sg_cpu->saved_idle_calls;
+	unsigned long idle_calls;
+	bool ret;
+
+	/*
+	 * The heuristics in this function is for the fair class. For SCX, the
+	 * performance target comes directly from the BPF scheduler. Let's just
+	 * follow it.
+	 */
+	if (scx_switched_all())
+		return false;
+
+	/* if capped by uclamp_max, always update to be in compliance */
+	if (uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)))
+		return false;
+
+	/*
+	 * Maintain the frequency if the CPU has not been idle recently, as
+	 * reduction is likely to be premature.
+	 */
+	idle_calls = tick_nohz_get_idle_calls_cpu(sg_cpu->cpu);
+	ret = idle_calls == sg_cpu->saved_idle_calls;
 
 	sg_cpu->saved_idle_calls = idle_calls;
 	return ret;
 }
 #else
-static inline bool sugov_cpu_is_busy(struct sugov_cpu *sg_cpu) { return false; }
+static inline bool sugov_hold_freq(struct sugov_cpu *sg_cpu) { return false; }
 #endif /* CONFIG_NO_HZ_COMMON */
 
 /*
@@ -382,14 +403,8 @@ static void sugov_update_single_freq(struct update_util_data *hook, u64 time,
 		return;
 
 	next_f = get_next_freq(sg_policy, sg_cpu->util, max_cap);
-	/*
-	 * Do not reduce the frequency if the CPU has not been idle
-	 * recently, as the reduction is likely to be premature then.
-	 *
-	 * Except when the rq is capped by uclamp_max.
-	 */
-	if (!uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)) &&
-	    sugov_cpu_is_busy(sg_cpu) && next_f < sg_policy->next_freq &&
+
+	if (sugov_hold_freq(sg_cpu) && next_f < sg_policy->next_freq &&
 	    !sg_policy->need_freq_update) {
 		next_f = sg_policy->next_freq;
 
@@ -436,14 +451,7 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
 	if (!sugov_update_single_common(sg_cpu, time, max_cap, flags))
 		return;
 
-	/*
-	 * Do not reduce the target performance level if the CPU has not been
-	 * idle recently, as the reduction is likely to be premature then.
-	 *
-	 * Except when the rq is capped by uclamp_max.
-	 */
-	if (!uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)) &&
-	    sugov_cpu_is_busy(sg_cpu) && sg_cpu->util < prev_util)
+	if (sugov_hold_freq(sg_cpu) && sg_cpu->util < prev_util)
 		sg_cpu->util = prev_util;
 
 	cpufreq_driver_adjust_perf(sg_cpu->cpu, sg_cpu->bw_min,
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 8d5d98a5834d..6f306e1c9c3e 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -1089,6 +1089,9 @@ void proc_sched_show_task(struct task_struct *p, struct pid_namespace *ns,
 		P(dl.runtime);
 		P(dl.deadline);
 	}
+#ifdef CONFIG_SCHED_CLASS_EXT
+	__PS("ext.enabled", task_on_scx(p));
+#endif
 #undef PN_SCHEDSTAT
 #undef P_SCHEDSTAT
 
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
new file mode 100644
index 000000000000..b9fd7b7d4a86
--- /dev/null
+++ b/kernel/sched/ext.c
@@ -0,0 +1,6537 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#define SCX_OP_IDX(op)		(offsetof(struct sched_ext_ops, op) / sizeof(void (*)(void)))
+
+enum scx_consts {
+	SCX_DSP_DFL_MAX_BATCH		= 32,
+	SCX_DSP_MAX_LOOPS		= 32,
+	SCX_WATCHDOG_MAX_TIMEOUT	= 30 * HZ,
+
+	SCX_EXIT_BT_LEN			= 64,
+	SCX_EXIT_MSG_LEN		= 1024,
+	SCX_EXIT_DUMP_DFL_LEN		= 32768,
+
+	SCX_CPUPERF_ONE			= SCHED_CAPACITY_SCALE,
+};
+
+enum scx_exit_kind {
+	SCX_EXIT_NONE,
+	SCX_EXIT_DONE,
+
+	SCX_EXIT_UNREG = 64,	/* user-space initiated unregistration */
+	SCX_EXIT_UNREG_BPF,	/* BPF-initiated unregistration */
+	SCX_EXIT_UNREG_KERN,	/* kernel-initiated unregistration */
+	SCX_EXIT_SYSRQ,		/* requested by 'S' sysrq */
+
+	SCX_EXIT_ERROR = 1024,	/* runtime error, error msg contains details */
+	SCX_EXIT_ERROR_BPF,	/* ERROR but triggered through scx_bpf_error() */
+	SCX_EXIT_ERROR_STALL,	/* watchdog detected stalled runnable tasks */
+};
+
+/*
+ * An exit code can be specified when exiting with scx_bpf_exit() or
+ * scx_ops_exit(), corresponding to exit_kind UNREG_BPF and UNREG_KERN
+ * respectively. The codes are 64bit of the format:
+ *
+ *   Bits: [63  ..  48 47   ..  32 31 .. 0]
+ *         [ SYS ACT ] [ SYS RSN ] [ USR  ]
+ *
+ *   SYS ACT: System-defined exit actions
+ *   SYS RSN: System-defined exit reasons
+ *   USR    : User-defined exit codes and reasons
+ *
+ * Using the above, users may communicate intention and context by ORing system
+ * actions and/or system reasons with a user-defined exit code.
+ */
+enum scx_exit_code {
+	/* Reasons */
+	SCX_ECODE_RSN_HOTPLUG	= 1LLU << 32,
+
+	/* Actions */
+	SCX_ECODE_ACT_RESTART	= 1LLU << 48,
+};
+
+/*
+ * scx_exit_info is passed to ops.exit() to describe why the BPF scheduler is
+ * being disabled.
+ */
+struct scx_exit_info {
+	/* %SCX_EXIT_* - broad category of the exit reason */
+	enum scx_exit_kind	kind;
+
+	/* exit code if gracefully exiting */
+	s64			exit_code;
+
+	/* textual representation of the above */
+	const char		*reason;
+
+	/* backtrace if exiting due to an error */
+	unsigned long		*bt;
+	u32			bt_len;
+
+	/* informational message */
+	char			*msg;
+
+	/* debug dump */
+	char			*dump;
+};
+
+/* sched_ext_ops.flags */
+enum scx_ops_flags {
+	/*
+	 * Keep built-in idle tracking even if ops.update_idle() is implemented.
+	 */
+	SCX_OPS_KEEP_BUILTIN_IDLE = 1LLU << 0,
+
+	/*
+	 * By default, if there are no other task to run on the CPU, ext core
+	 * keeps running the current task even after its slice expires. If this
+	 * flag is specified, such tasks are passed to ops.enqueue() with
+	 * %SCX_ENQ_LAST. See the comment above %SCX_ENQ_LAST for more info.
+	 */
+	SCX_OPS_ENQ_LAST	= 1LLU << 1,
+
+	/*
+	 * An exiting task may schedule after PF_EXITING is set. In such cases,
+	 * bpf_task_from_pid() may not be able to find the task and if the BPF
+	 * scheduler depends on pid lookup for dispatching, the task will be
+	 * lost leading to various issues including RCU grace period stalls.
+	 *
+	 * To mask this problem, by default, unhashed tasks are automatically
+	 * dispatched to the local DSQ on enqueue. If the BPF scheduler doesn't
+	 * depend on pid lookups and wants to handle these tasks directly, the
+	 * following flag can be used.
+	 */
+	SCX_OPS_ENQ_EXITING	= 1LLU << 2,
+
+	/*
+	 * If set, only tasks with policy set to SCHED_EXT are attached to
+	 * sched_ext. If clear, SCHED_NORMAL tasks are also included.
+	 */
+	SCX_OPS_SWITCH_PARTIAL	= 1LLU << 3,
+
+	SCX_OPS_ALL_FLAGS	= SCX_OPS_KEEP_BUILTIN_IDLE |
+				  SCX_OPS_ENQ_LAST |
+				  SCX_OPS_ENQ_EXITING |
+				  SCX_OPS_SWITCH_PARTIAL,
+};
+
+/* argument container for ops.init_task() */
+struct scx_init_task_args {
+	/*
+	 * Set if ops.init_task() is being invoked on the fork path, as opposed
+	 * to the scheduler transition path.
+	 */
+	bool			fork;
+};
+
+/* argument container for ops.exit_task() */
+struct scx_exit_task_args {
+	/* Whether the task exited before running on sched_ext. */
+	bool cancelled;
+};
+
+enum scx_cpu_preempt_reason {
+	/* next task is being scheduled by &sched_class_rt */
+	SCX_CPU_PREEMPT_RT,
+	/* next task is being scheduled by &sched_class_dl */
+	SCX_CPU_PREEMPT_DL,
+	/* next task is being scheduled by &sched_class_stop */
+	SCX_CPU_PREEMPT_STOP,
+	/* unknown reason for SCX being preempted */
+	SCX_CPU_PREEMPT_UNKNOWN,
+};
+
+/*
+ * Argument container for ops->cpu_acquire(). Currently empty, but may be
+ * expanded in the future.
+ */
+struct scx_cpu_acquire_args {};
+
+/* argument container for ops->cpu_release() */
+struct scx_cpu_release_args {
+	/* the reason the CPU was preempted */
+	enum scx_cpu_preempt_reason reason;
+
+	/* the task that's going to be scheduled on the CPU */
+	struct task_struct	*task;
+};
+
+/*
+ * Informational context provided to dump operations.
+ */
+struct scx_dump_ctx {
+	enum scx_exit_kind	kind;
+	s64			exit_code;
+	const char		*reason;
+	u64			at_ns;
+	u64			at_jiffies;
+};
+
+/**
+ * struct sched_ext_ops - Operation table for BPF scheduler implementation
+ *
+ * Userland can implement an arbitrary scheduling policy by implementing and
+ * loading operations in this table.
+ */
+struct sched_ext_ops {
+	/**
+	 * select_cpu - Pick the target CPU for a task which is being woken up
+	 * @p: task being woken up
+	 * @prev_cpu: the cpu @p was on before sleeping
+	 * @wake_flags: SCX_WAKE_*
+	 *
+	 * Decision made here isn't final. @p may be moved to any CPU while it
+	 * is getting dispatched for execution later. However, as @p is not on
+	 * the rq at this point, getting the eventual execution CPU right here
+	 * saves a small bit of overhead down the line.
+	 *
+	 * If an idle CPU is returned, the CPU is kicked and will try to
+	 * dispatch. While an explicit custom mechanism can be added,
+	 * select_cpu() serves as the default way to wake up idle CPUs.
+	 *
+	 * @p may be dispatched directly by calling scx_bpf_dispatch(). If @p
+	 * is dispatched, the ops.enqueue() callback will be skipped. Finally,
+	 * if @p is dispatched to SCX_DSQ_LOCAL, it will be dispatched to the
+	 * local DSQ of whatever CPU is returned by this callback.
+	 */
+	s32 (*select_cpu)(struct task_struct *p, s32 prev_cpu, u64 wake_flags);
+
+	/**
+	 * enqueue - Enqueue a task on the BPF scheduler
+	 * @p: task being enqueued
+	 * @enq_flags: %SCX_ENQ_*
+	 *
+	 * @p is ready to run. Dispatch directly by calling scx_bpf_dispatch()
+	 * or enqueue on the BPF scheduler. If not directly dispatched, the bpf
+	 * scheduler owns @p and if it fails to dispatch @p, the task will
+	 * stall.
+	 *
+	 * If @p was dispatched from ops.select_cpu(), this callback is
+	 * skipped.
+	 */
+	void (*enqueue)(struct task_struct *p, u64 enq_flags);
+
+	/**
+	 * dequeue - Remove a task from the BPF scheduler
+	 * @p: task being dequeued
+	 * @deq_flags: %SCX_DEQ_*
+	 *
+	 * Remove @p from the BPF scheduler. This is usually called to isolate
+	 * the task while updating its scheduling properties (e.g. priority).
+	 *
+	 * The ext core keeps track of whether the BPF side owns a given task or
+	 * not and can gracefully ignore spurious dispatches from BPF side,
+	 * which makes it safe to not implement this method. However, depending
+	 * on the scheduling logic, this can lead to confusing behaviors - e.g.
+	 * scheduling position not being updated across a priority change.
+	 */
+	void (*dequeue)(struct task_struct *p, u64 deq_flags);
+
+	/**
+	 * dispatch - Dispatch tasks from the BPF scheduler and/or consume DSQs
+	 * @cpu: CPU to dispatch tasks for
+	 * @prev: previous task being switched out
+	 *
+	 * Called when a CPU's local dsq is empty. The operation should dispatch
+	 * one or more tasks from the BPF scheduler into the DSQs using
+	 * scx_bpf_dispatch() and/or consume user DSQs into the local DSQ using
+	 * scx_bpf_consume().
+	 *
+	 * The maximum number of times scx_bpf_dispatch() can be called without
+	 * an intervening scx_bpf_consume() is specified by
+	 * ops.dispatch_max_batch. See the comments on top of the two functions
+	 * for more details.
+	 *
+	 * When not %NULL, @prev is an SCX task with its slice depleted. If
+	 * @prev is still runnable as indicated by set %SCX_TASK_QUEUED in
+	 * @prev->scx.flags, it is not enqueued yet and will be enqueued after
+	 * ops.dispatch() returns. To keep executing @prev, return without
+	 * dispatching or consuming any tasks. Also see %SCX_OPS_ENQ_LAST.
+	 */
+	void (*dispatch)(s32 cpu, struct task_struct *prev);
+
+	/**
+	 * tick - Periodic tick
+	 * @p: task running currently
+	 *
+	 * This operation is called every 1/HZ seconds on CPUs which are
+	 * executing an SCX task. Setting @p->scx.slice to 0 will trigger an
+	 * immediate dispatch cycle on the CPU.
+	 */
+	void (*tick)(struct task_struct *p);
+
+	/**
+	 * runnable - A task is becoming runnable on its associated CPU
+	 * @p: task becoming runnable
+	 * @enq_flags: %SCX_ENQ_*
+	 *
+	 * This and the following three functions can be used to track a task's
+	 * execution state transitions. A task becomes ->runnable() on a CPU,
+	 * and then goes through one or more ->running() and ->stopping() pairs
+	 * as it runs on the CPU, and eventually becomes ->quiescent() when it's
+	 * done running on the CPU.
+	 *
+	 * @p is becoming runnable on the CPU because it's
+	 *
+	 * - waking up (%SCX_ENQ_WAKEUP)
+	 * - being moved from another CPU
+	 * - being restored after temporarily taken off the queue for an
+	 *   attribute change.
+	 *
+	 * This and ->enqueue() are related but not coupled. This operation
+	 * notifies @p's state transition and may not be followed by ->enqueue()
+	 * e.g. when @p is being dispatched to a remote CPU, or when @p is
+	 * being enqueued on a CPU experiencing a hotplug event. Likewise, a
+	 * task may be ->enqueue()'d without being preceded by this operation
+	 * e.g. after exhausting its slice.
+	 */
+	void (*runnable)(struct task_struct *p, u64 enq_flags);
+
+	/**
+	 * running - A task is starting to run on its associated CPU
+	 * @p: task starting to run
+	 *
+	 * See ->runnable() for explanation on the task state notifiers.
+	 */
+	void (*running)(struct task_struct *p);
+
+	/**
+	 * stopping - A task is stopping execution
+	 * @p: task stopping to run
+	 * @runnable: is task @p still runnable?
+	 *
+	 * See ->runnable() for explanation on the task state notifiers. If
+	 * !@runnable, ->quiescent() will be invoked after this operation
+	 * returns.
+	 */
+	void (*stopping)(struct task_struct *p, bool runnable);
+
+	/**
+	 * quiescent - A task is becoming not runnable on its associated CPU
+	 * @p: task becoming not runnable
+	 * @deq_flags: %SCX_DEQ_*
+	 *
+	 * See ->runnable() for explanation on the task state notifiers.
+	 *
+	 * @p is becoming quiescent on the CPU because it's
+	 *
+	 * - sleeping (%SCX_DEQ_SLEEP)
+	 * - being moved to another CPU
+	 * - being temporarily taken off the queue for an attribute change
+	 *   (%SCX_DEQ_SAVE)
+	 *
+	 * This and ->dequeue() are related but not coupled. This operation
+	 * notifies @p's state transition and may not be preceded by ->dequeue()
+	 * e.g. when @p is being dispatched to a remote CPU.
+	 */
+	void (*quiescent)(struct task_struct *p, u64 deq_flags);
+
+	/**
+	 * yield - Yield CPU
+	 * @from: yielding task
+	 * @to: optional yield target task
+	 *
+	 * If @to is NULL, @from is yielding the CPU to other runnable tasks.
+	 * The BPF scheduler should ensure that other available tasks are
+	 * dispatched before the yielding task. Return value is ignored in this
+	 * case.
+	 *
+	 * If @to is not-NULL, @from wants to yield the CPU to @to. If the bpf
+	 * scheduler can implement the request, return %true; otherwise, %false.
+	 */
+	bool (*yield)(struct task_struct *from, struct task_struct *to);
+
+	/**
+	 * core_sched_before - Task ordering for core-sched
+	 * @a: task A
+	 * @b: task B
+	 *
+	 * Used by core-sched to determine the ordering between two tasks. See
+	 * Documentation/admin-guide/hw-vuln/core-scheduling.rst for details on
+	 * core-sched.
+	 *
+	 * Both @a and @b are runnable and may or may not currently be queued on
+	 * the BPF scheduler. Should return %true if @a should run before @b.
+	 * %false if there's no required ordering or @b should run before @a.
+	 *
+	 * If not specified, the default is ordering them according to when they
+	 * became runnable.
+	 */
+	bool (*core_sched_before)(struct task_struct *a, struct task_struct *b);
+
+	/**
+	 * set_weight - Set task weight
+	 * @p: task to set weight for
+	 * @weight: new weight [1..10000]
+	 *
+	 * Update @p's weight to @weight.
+	 */
+	void (*set_weight)(struct task_struct *p, u32 weight);
+
+	/**
+	 * set_cpumask - Set CPU affinity
+	 * @p: task to set CPU affinity for
+	 * @cpumask: cpumask of cpus that @p can run on
+	 *
+	 * Update @p's CPU affinity to @cpumask.
+	 */
+	void (*set_cpumask)(struct task_struct *p,
+			    const struct cpumask *cpumask);
+
+	/**
+	 * update_idle - Update the idle state of a CPU
+	 * @cpu: CPU to udpate the idle state for
+	 * @idle: whether entering or exiting the idle state
+	 *
+	 * This operation is called when @rq's CPU goes or leaves the idle
+	 * state. By default, implementing this operation disables the built-in
+	 * idle CPU tracking and the following helpers become unavailable:
+	 *
+	 * - scx_bpf_select_cpu_dfl()
+	 * - scx_bpf_test_and_clear_cpu_idle()
+	 * - scx_bpf_pick_idle_cpu()
+	 *
+	 * The user also must implement ops.select_cpu() as the default
+	 * implementation relies on scx_bpf_select_cpu_dfl().
+	 *
+	 * Specify the %SCX_OPS_KEEP_BUILTIN_IDLE flag to keep the built-in idle
+	 * tracking.
+	 */
+	void (*update_idle)(s32 cpu, bool idle);
+
+	/**
+	 * cpu_acquire - A CPU is becoming available to the BPF scheduler
+	 * @cpu: The CPU being acquired by the BPF scheduler.
+	 * @args: Acquire arguments, see the struct definition.
+	 *
+	 * A CPU that was previously released from the BPF scheduler is now once
+	 * again under its control.
+	 */
+	void (*cpu_acquire)(s32 cpu, struct scx_cpu_acquire_args *args);
+
+	/**
+	 * cpu_release - A CPU is taken away from the BPF scheduler
+	 * @cpu: The CPU being released by the BPF scheduler.
+	 * @args: Release arguments, see the struct definition.
+	 *
+	 * The specified CPU is no longer under the control of the BPF
+	 * scheduler. This could be because it was preempted by a higher
+	 * priority sched_class, though there may be other reasons as well. The
+	 * caller should consult @args->reason to determine the cause.
+	 */
+	void (*cpu_release)(s32 cpu, struct scx_cpu_release_args *args);
+
+	/**
+	 * init_task - Initialize a task to run in a BPF scheduler
+	 * @p: task to initialize for BPF scheduling
+	 * @args: init arguments, see the struct definition
+	 *
+	 * Either we're loading a BPF scheduler or a new task is being forked.
+	 * Initialize @p for BPF scheduling. This operation may block and can
+	 * be used for allocations, and is called exactly once for a task.
+	 *
+	 * Return 0 for success, -errno for failure. An error return while
+	 * loading will abort loading of the BPF scheduler. During a fork, it
+	 * will abort that specific fork.
+	 */
+	s32 (*init_task)(struct task_struct *p, struct scx_init_task_args *args);
+
+	/**
+	 * exit_task - Exit a previously-running task from the system
+	 * @p: task to exit
+	 *
+	 * @p is exiting or the BPF scheduler is being unloaded. Perform any
+	 * necessary cleanup for @p.
+	 */
+	void (*exit_task)(struct task_struct *p, struct scx_exit_task_args *args);
+
+	/**
+	 * enable - Enable BPF scheduling for a task
+	 * @p: task to enable BPF scheduling for
+	 *
+	 * Enable @p for BPF scheduling. enable() is called on @p any time it
+	 * enters SCX, and is always paired with a matching disable().
+	 */
+	void (*enable)(struct task_struct *p);
+
+	/**
+	 * disable - Disable BPF scheduling for a task
+	 * @p: task to disable BPF scheduling for
+	 *
+	 * @p is exiting, leaving SCX or the BPF scheduler is being unloaded.
+	 * Disable BPF scheduling for @p. A disable() call is always matched
+	 * with a prior enable() call.
+	 */
+	void (*disable)(struct task_struct *p);
+
+	/**
+	 * dump - Dump BPF scheduler state on error
+	 * @ctx: debug dump context
+	 *
+	 * Use scx_bpf_dump() to generate BPF scheduler specific debug dump.
+	 */
+	void (*dump)(struct scx_dump_ctx *ctx);
+
+	/**
+	 * dump_cpu - Dump BPF scheduler state for a CPU on error
+	 * @ctx: debug dump context
+	 * @cpu: CPU to generate debug dump for
+	 * @idle: @cpu is currently idle without any runnable tasks
+	 *
+	 * Use scx_bpf_dump() to generate BPF scheduler specific debug dump for
+	 * @cpu. If @idle is %true and this operation doesn't produce any
+	 * output, @cpu is skipped for dump.
+	 */
+	void (*dump_cpu)(struct scx_dump_ctx *ctx, s32 cpu, bool idle);
+
+	/**
+	 * dump_task - Dump BPF scheduler state for a runnable task on error
+	 * @ctx: debug dump context
+	 * @p: runnable task to generate debug dump for
+	 *
+	 * Use scx_bpf_dump() to generate BPF scheduler specific debug dump for
+	 * @p.
+	 */
+	void (*dump_task)(struct scx_dump_ctx *ctx, struct task_struct *p);
+
+	/*
+	 * All online ops must come before ops.cpu_online().
+	 */
+
+	/**
+	 * cpu_online - A CPU became online
+	 * @cpu: CPU which just came up
+	 *
+	 * @cpu just came online. @cpu will not call ops.enqueue() or
+	 * ops.dispatch(), nor run tasks associated with other CPUs beforehand.
+	 */
+	void (*cpu_online)(s32 cpu);
+
+	/**
+	 * cpu_offline - A CPU is going offline
+	 * @cpu: CPU which is going offline
+	 *
+	 * @cpu is going offline. @cpu will not call ops.enqueue() or
+	 * ops.dispatch(), nor run tasks associated with other CPUs afterwards.
+	 */
+	void (*cpu_offline)(s32 cpu);
+
+	/*
+	 * All CPU hotplug ops must come before ops.init().
+	 */
+
+	/**
+	 * init - Initialize the BPF scheduler
+	 */
+	s32 (*init)(void);
+
+	/**
+	 * exit - Clean up after the BPF scheduler
+	 * @info: Exit info
+	 */
+	void (*exit)(struct scx_exit_info *info);
+
+	/**
+	 * dispatch_max_batch - Max nr of tasks that dispatch() can dispatch
+	 */
+	u32 dispatch_max_batch;
+
+	/**
+	 * flags - %SCX_OPS_* flags
+	 */
+	u64 flags;
+
+	/**
+	 * timeout_ms - The maximum amount of time, in milliseconds, that a
+	 * runnable task should be able to wait before being scheduled. The
+	 * maximum timeout may not exceed the default timeout of 30 seconds.
+	 *
+	 * Defaults to the maximum allowed timeout value of 30 seconds.
+	 */
+	u32 timeout_ms;
+
+	/**
+	 * exit_dump_len - scx_exit_info.dump buffer length. If 0, the default
+	 * value of 32768 is used.
+	 */
+	u32 exit_dump_len;
+
+	/**
+	 * hotplug_seq - A sequence number that may be set by the scheduler to
+	 * detect when a hotplug event has occurred during the loading process.
+	 * If 0, no detection occurs. Otherwise, the scheduler will fail to
+	 * load if the sequence number does not match @scx_hotplug_seq on the
+	 * enable path.
+	 */
+	u64 hotplug_seq;
+
+	/**
+	 * name - BPF scheduler's name
+	 *
+	 * Must be a non-zero valid BPF object name including only isalnum(),
+	 * '_' and '.' chars. Shows up in kernel.sched_ext_ops sysctl while the
+	 * BPF scheduler is enabled.
+	 */
+	char name[SCX_OPS_NAME_LEN];
+};
+
+enum scx_opi {
+	SCX_OPI_BEGIN			= 0,
+	SCX_OPI_NORMAL_BEGIN		= 0,
+	SCX_OPI_NORMAL_END		= SCX_OP_IDX(cpu_online),
+	SCX_OPI_CPU_HOTPLUG_BEGIN	= SCX_OP_IDX(cpu_online),
+	SCX_OPI_CPU_HOTPLUG_END		= SCX_OP_IDX(init),
+	SCX_OPI_END			= SCX_OP_IDX(init),
+};
+
+enum scx_wake_flags {
+	/* expose select WF_* flags as enums */
+	SCX_WAKE_FORK		= WF_FORK,
+	SCX_WAKE_TTWU		= WF_TTWU,
+	SCX_WAKE_SYNC		= WF_SYNC,
+};
+
+enum scx_enq_flags {
+	/* expose select ENQUEUE_* flags as enums */
+	SCX_ENQ_WAKEUP		= ENQUEUE_WAKEUP,
+	SCX_ENQ_HEAD		= ENQUEUE_HEAD,
+
+	/* high 32bits are SCX specific */
+
+	/*
+	 * Set the following to trigger preemption when calling
+	 * scx_bpf_dispatch() with a local dsq as the target. The slice of the
+	 * current task is cleared to zero and the CPU is kicked into the
+	 * scheduling path. Implies %SCX_ENQ_HEAD.
+	 */
+	SCX_ENQ_PREEMPT		= 1LLU << 32,
+
+	/*
+	 * The task being enqueued was previously enqueued on the current CPU's
+	 * %SCX_DSQ_LOCAL, but was removed from it in a call to the
+	 * bpf_scx_reenqueue_local() kfunc. If bpf_scx_reenqueue_local() was
+	 * invoked in a ->cpu_release() callback, and the task is again
+	 * dispatched back to %SCX_LOCAL_DSQ by this current ->enqueue(), the
+	 * task will not be scheduled on the CPU until at least the next invocation
+	 * of the ->cpu_acquire() callback.
+	 */
+	SCX_ENQ_REENQ		= 1LLU << 40,
+
+	/*
+	 * The task being enqueued is the only task available for the cpu. By
+	 * default, ext core keeps executing such tasks but when
+	 * %SCX_OPS_ENQ_LAST is specified, they're ops.enqueue()'d with the
+	 * %SCX_ENQ_LAST flag set.
+	 *
+	 * If the BPF scheduler wants to continue executing the task,
+	 * ops.enqueue() should dispatch the task to %SCX_DSQ_LOCAL immediately.
+	 * If the task gets queued on a different dsq or the BPF side, the BPF
+	 * scheduler is responsible for triggering a follow-up scheduling event.
+	 * Otherwise, Execution may stall.
+	 */
+	SCX_ENQ_LAST		= 1LLU << 41,
+
+	/* high 8 bits are internal */
+	__SCX_ENQ_INTERNAL_MASK	= 0xffLLU << 56,
+
+	SCX_ENQ_CLEAR_OPSS	= 1LLU << 56,
+	SCX_ENQ_DSQ_PRIQ	= 1LLU << 57,
+};
+
+enum scx_deq_flags {
+	/* expose select DEQUEUE_* flags as enums */
+	SCX_DEQ_SLEEP		= DEQUEUE_SLEEP,
+
+	/* high 32bits are SCX specific */
+
+	/*
+	 * The generic core-sched layer decided to execute the task even though
+	 * it hasn't been dispatched yet. Dequeue from the BPF side.
+	 */
+	SCX_DEQ_CORE_SCHED_EXEC	= 1LLU << 32,
+};
+
+enum scx_pick_idle_cpu_flags {
+	SCX_PICK_IDLE_CORE	= 1LLU << 0,	/* pick a CPU whose SMT siblings are also idle */
+};
+
+enum scx_kick_flags {
+	/*
+	 * Kick the target CPU if idle. Guarantees that the target CPU goes
+	 * through at least one full scheduling cycle before going idle. If the
+	 * target CPU can be determined to be currently not idle and going to go
+	 * through a scheduling cycle before going idle, noop.
+	 */
+	SCX_KICK_IDLE		= 1LLU << 0,
+
+	/*
+	 * Preempt the current task and execute the dispatch path. If the
+	 * current task of the target CPU is an SCX task, its ->scx.slice is
+	 * cleared to zero before the scheduling path is invoked so that the
+	 * task expires and the dispatch path is invoked.
+	 */
+	SCX_KICK_PREEMPT	= 1LLU << 1,
+
+	/*
+	 * Wait for the CPU to be rescheduled. The scx_bpf_kick_cpu() call will
+	 * return after the target CPU finishes picking the next task.
+	 */
+	SCX_KICK_WAIT		= 1LLU << 2,
+};
+
+enum scx_ops_enable_state {
+	SCX_OPS_PREPPING,
+	SCX_OPS_ENABLING,
+	SCX_OPS_ENABLED,
+	SCX_OPS_DISABLING,
+	SCX_OPS_DISABLED,
+};
+
+static const char *scx_ops_enable_state_str[] = {
+	[SCX_OPS_PREPPING]	= "prepping",
+	[SCX_OPS_ENABLING]	= "enabling",
+	[SCX_OPS_ENABLED]	= "enabled",
+	[SCX_OPS_DISABLING]	= "disabling",
+	[SCX_OPS_DISABLED]	= "disabled",
+};
+
+/*
+ * sched_ext_entity->ops_state
+ *
+ * Used to track the task ownership between the SCX core and the BPF scheduler.
+ * State transitions look as follows:
+ *
+ * NONE -> QUEUEING -> QUEUED -> DISPATCHING
+ *   ^              |                 |
+ *   |              v                 v
+ *   \-------------------------------/
+ *
+ * QUEUEING and DISPATCHING states can be waited upon. See wait_ops_state() call
+ * sites for explanations on the conditions being waited upon and why they are
+ * safe. Transitions out of them into NONE or QUEUED must store_release and the
+ * waiters should load_acquire.
+ *
+ * Tracking scx_ops_state enables sched_ext core to reliably determine whether
+ * any given task can be dispatched by the BPF scheduler at all times and thus
+ * relaxes the requirements on the BPF scheduler. This allows the BPF scheduler
+ * to try to dispatch any task anytime regardless of its state as the SCX core
+ * can safely reject invalid dispatches.
+ */
+enum scx_ops_state {
+	SCX_OPSS_NONE,		/* owned by the SCX core */
+	SCX_OPSS_QUEUEING,	/* in transit to the BPF scheduler */
+	SCX_OPSS_QUEUED,	/* owned by the BPF scheduler */
+	SCX_OPSS_DISPATCHING,	/* in transit back to the SCX core */
+
+	/*
+	 * QSEQ brands each QUEUED instance so that, when dispatch races
+	 * dequeue/requeue, the dispatcher can tell whether it still has a claim
+	 * on the task being dispatched.
+	 *
+	 * As some 32bit archs can't do 64bit store_release/load_acquire,
+	 * p->scx.ops_state is atomic_long_t which leaves 30 bits for QSEQ on
+	 * 32bit machines. The dispatch race window QSEQ protects is very narrow
+	 * and runs with IRQ disabled. 30 bits should be sufficient.
+	 */
+	SCX_OPSS_QSEQ_SHIFT	= 2,
+};
+
+/* Use macros to ensure that the type is unsigned long for the masks */
+#define SCX_OPSS_STATE_MASK	((1LU << SCX_OPSS_QSEQ_SHIFT) - 1)
+#define SCX_OPSS_QSEQ_MASK	(~SCX_OPSS_STATE_MASK)
+
+/*
+ * During exit, a task may schedule after losing its PIDs. When disabling the
+ * BPF scheduler, we need to be able to iterate tasks in every state to
+ * guarantee system safety. Maintain a dedicated task list which contains every
+ * task between its fork and eventual free.
+ */
+static DEFINE_SPINLOCK(scx_tasks_lock);
+static LIST_HEAD(scx_tasks);
+
+/* ops enable/disable */
+static struct kthread_worker *scx_ops_helper;
+static DEFINE_MUTEX(scx_ops_enable_mutex);
+DEFINE_STATIC_KEY_FALSE(__scx_ops_enabled);
+DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem);
+static atomic_t scx_ops_enable_state_var = ATOMIC_INIT(SCX_OPS_DISABLED);
+static atomic_t scx_ops_bypass_depth = ATOMIC_INIT(0);
+static bool scx_switching_all;
+DEFINE_STATIC_KEY_FALSE(__scx_switched_all);
+
+static struct sched_ext_ops scx_ops;
+static bool scx_warned_zero_slice;
+
+static DEFINE_STATIC_KEY_FALSE(scx_ops_enq_last);
+static DEFINE_STATIC_KEY_FALSE(scx_ops_enq_exiting);
+static DEFINE_STATIC_KEY_FALSE(scx_ops_cpu_preempt);
+static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);
+
+struct static_key_false scx_has_op[SCX_OPI_END] =
+	{ [0 ... SCX_OPI_END-1] = STATIC_KEY_FALSE_INIT };
+
+static atomic_t scx_exit_kind = ATOMIC_INIT(SCX_EXIT_DONE);
+static struct scx_exit_info *scx_exit_info;
+
+static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0);
+static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0);
+
+/*
+ * The maximum amount of time in jiffies that a task may be runnable without
+ * being scheduled on a CPU. If this timeout is exceeded, it will trigger
+ * scx_ops_error().
+ */
+static unsigned long scx_watchdog_timeout;
+
+/*
+ * The last time the delayed work was run. This delayed work relies on
+ * ksoftirqd being able to run to service timer interrupts, so it's possible
+ * that this work itself could get wedged. To account for this, we check that
+ * it's not stalled in the timer tick, and trigger an error if it is.
+ */
+static unsigned long scx_watchdog_timestamp = INITIAL_JIFFIES;
+
+static struct delayed_work scx_watchdog_work;
+
+/* idle tracking */
+#ifdef CONFIG_SMP
+#ifdef CONFIG_CPUMASK_OFFSTACK
+#define CL_ALIGNED_IF_ONSTACK
+#else
+#define CL_ALIGNED_IF_ONSTACK __cacheline_aligned_in_smp
+#endif
+
+static struct {
+	cpumask_var_t cpu;
+	cpumask_var_t smt;
+} idle_masks CL_ALIGNED_IF_ONSTACK;
+
+#endif	/* CONFIG_SMP */
+
+/* for %SCX_KICK_WAIT */
+static unsigned long __percpu *scx_kick_cpus_pnt_seqs;
+
+/*
+ * Direct dispatch marker.
+ *
+ * Non-NULL values are used for direct dispatch from enqueue path. A valid
+ * pointer points to the task currently being enqueued. An ERR_PTR value is used
+ * to indicate that direct dispatch has already happened.
+ */
+static DEFINE_PER_CPU(struct task_struct *, direct_dispatch_task);
+
+/* dispatch queues */
+static struct scx_dispatch_q __cacheline_aligned_in_smp scx_dsq_global;
+
+static const struct rhashtable_params dsq_hash_params = {
+	.key_len		= 8,
+	.key_offset		= offsetof(struct scx_dispatch_q, id),
+	.head_offset		= offsetof(struct scx_dispatch_q, hash_node),
+};
+
+static struct rhashtable dsq_hash;
+static LLIST_HEAD(dsqs_to_free);
+
+/* dispatch buf */
+struct scx_dsp_buf_ent {
+	struct task_struct	*task;
+	unsigned long		qseq;
+	u64			dsq_id;
+	u64			enq_flags;
+};
+
+static u32 scx_dsp_max_batch;
+
+struct scx_dsp_ctx {
+	struct rq		*rq;
+	u32			cursor;
+	u32			nr_tasks;
+	struct scx_dsp_buf_ent	buf[];
+};
+
+static struct scx_dsp_ctx __percpu *scx_dsp_ctx;
+
+/* string formatting from BPF */
+struct scx_bstr_buf {
+	u64			data[MAX_BPRINTF_VARARGS];
+	char			line[SCX_EXIT_MSG_LEN];
+};
+
+static DEFINE_RAW_SPINLOCK(scx_exit_bstr_buf_lock);
+static struct scx_bstr_buf scx_exit_bstr_buf;
+
+/* ops debug dump */
+struct scx_dump_data {
+	s32			cpu;
+	bool			first;
+	s32			cursor;
+	struct seq_buf		*s;
+	const char		*prefix;
+	struct scx_bstr_buf	buf;
+};
+
+struct scx_dump_data scx_dump_data = {
+	.cpu			= -1,
+};
+
+/* /sys/kernel/sched_ext interface */
+static struct kset *scx_kset;
+static struct kobject *scx_root_kobj;
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/sched_ext.h>
+
+static void process_ddsp_deferred_locals(struct rq *rq);
+static void scx_bpf_kick_cpu(s32 cpu, u64 flags);
+static __printf(3, 4) void scx_ops_exit_kind(enum scx_exit_kind kind,
+					     s64 exit_code,
+					     const char *fmt, ...);
+
+#define scx_ops_error_kind(err, fmt, args...)					\
+	scx_ops_exit_kind((err), 0, fmt, ##args)
+
+#define scx_ops_exit(code, fmt, args...)					\
+	scx_ops_exit_kind(SCX_EXIT_UNREG_KERN, (code), fmt, ##args)
+
+#define scx_ops_error(fmt, args...)						\
+	scx_ops_error_kind(SCX_EXIT_ERROR, fmt, ##args)
+
+#define SCX_HAS_OP(op)	static_branch_likely(&scx_has_op[SCX_OP_IDX(op)])
+
+static long jiffies_delta_msecs(unsigned long at, unsigned long now)
+{
+	if (time_after(at, now))
+		return jiffies_to_msecs(at - now);
+	else
+		return -(long)jiffies_to_msecs(now - at);
+}
+
+/* if the highest set bit is N, return a mask with bits [N+1, 31] set */
+static u32 higher_bits(u32 flags)
+{
+	return ~((1 << fls(flags)) - 1);
+}
+
+/* return the mask with only the highest bit set */
+static u32 highest_bit(u32 flags)
+{
+	int bit = fls(flags);
+	return ((u64)1 << bit) >> 1;
+}
+
+static bool u32_before(u32 a, u32 b)
+{
+	return (s32)(a - b) < 0;
+}
+
+/*
+ * scx_kf_mask enforcement. Some kfuncs can only be called from specific SCX
+ * ops. When invoking SCX ops, SCX_CALL_OP[_RET]() should be used to indicate
+ * the allowed kfuncs and those kfuncs should use scx_kf_allowed() to check
+ * whether it's running from an allowed context.
+ *
+ * @mask is constant, always inline to cull the mask calculations.
+ */
+static __always_inline void scx_kf_allow(u32 mask)
+{
+	/* nesting is allowed only in increasing scx_kf_mask order */
+	WARN_ONCE((mask | higher_bits(mask)) & current->scx.kf_mask,
+		  "invalid nesting current->scx.kf_mask=0x%x mask=0x%x\n",
+		  current->scx.kf_mask, mask);
+	current->scx.kf_mask |= mask;
+	barrier();
+}
+
+static void scx_kf_disallow(u32 mask)
+{
+	barrier();
+	current->scx.kf_mask &= ~mask;
+}
+
+#define SCX_CALL_OP(mask, op, args...)						\
+do {										\
+	if (mask) {								\
+		scx_kf_allow(mask);						\
+		scx_ops.op(args);						\
+		scx_kf_disallow(mask);						\
+	} else {								\
+		scx_ops.op(args);						\
+	}									\
+} while (0)
+
+#define SCX_CALL_OP_RET(mask, op, args...)					\
+({										\
+	__typeof__(scx_ops.op(args)) __ret;					\
+	if (mask) {								\
+		scx_kf_allow(mask);						\
+		__ret = scx_ops.op(args);					\
+		scx_kf_disallow(mask);						\
+	} else {								\
+		__ret = scx_ops.op(args);					\
+	}									\
+	__ret;									\
+})
+
+/*
+ * Some kfuncs are allowed only on the tasks that are subjects of the
+ * in-progress scx_ops operation for, e.g., locking guarantees. To enforce such
+ * restrictions, the following SCX_CALL_OP_*() variants should be used when
+ * invoking scx_ops operations that take task arguments. These can only be used
+ * for non-nesting operations due to the way the tasks are tracked.
+ *
+ * kfuncs which can only operate on such tasks can in turn use
+ * scx_kf_allowed_on_arg_tasks() to test whether the invocation is allowed on
+ * the specific task.
+ */
+#define SCX_CALL_OP_TASK(mask, op, task, args...)				\
+do {										\
+	BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL);				\
+	current->scx.kf_tasks[0] = task;					\
+	SCX_CALL_OP(mask, op, task, ##args);					\
+	current->scx.kf_tasks[0] = NULL;					\
+} while (0)
+
+#define SCX_CALL_OP_TASK_RET(mask, op, task, args...)				\
+({										\
+	__typeof__(scx_ops.op(task, ##args)) __ret;				\
+	BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL);				\
+	current->scx.kf_tasks[0] = task;					\
+	__ret = SCX_CALL_OP_RET(mask, op, task, ##args);			\
+	current->scx.kf_tasks[0] = NULL;					\
+	__ret;									\
+})
+
+#define SCX_CALL_OP_2TASKS_RET(mask, op, task0, task1, args...)			\
+({										\
+	__typeof__(scx_ops.op(task0, task1, ##args)) __ret;			\
+	BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL);				\
+	current->scx.kf_tasks[0] = task0;					\
+	current->scx.kf_tasks[1] = task1;					\
+	__ret = SCX_CALL_OP_RET(mask, op, task0, task1, ##args);		\
+	current->scx.kf_tasks[0] = NULL;					\
+	current->scx.kf_tasks[1] = NULL;					\
+	__ret;									\
+})
+
+/* @mask is constant, always inline to cull unnecessary branches */
+static __always_inline bool scx_kf_allowed(u32 mask)
+{
+	if (unlikely(!(current->scx.kf_mask & mask))) {
+		scx_ops_error("kfunc with mask 0x%x called from an operation only allowing 0x%x",
+			      mask, current->scx.kf_mask);
+		return false;
+	}
+
+	if (unlikely((mask & SCX_KF_SLEEPABLE) && in_interrupt())) {
+		scx_ops_error("sleepable kfunc called from non-sleepable context");
+		return false;
+	}
+
+	/*
+	 * Enforce nesting boundaries. e.g. A kfunc which can be called from
+	 * DISPATCH must not be called if we're running DEQUEUE which is nested
+	 * inside ops.dispatch(). We don't need to check the SCX_KF_SLEEPABLE
+	 * boundary thanks to the above in_interrupt() check.
+	 */
+	if (unlikely(highest_bit(mask) == SCX_KF_CPU_RELEASE &&
+		     (current->scx.kf_mask & higher_bits(SCX_KF_CPU_RELEASE)))) {
+		scx_ops_error("cpu_release kfunc called from a nested operation");
+		return false;
+	}
+
+	if (unlikely(highest_bit(mask) == SCX_KF_DISPATCH &&
+		     (current->scx.kf_mask & higher_bits(SCX_KF_DISPATCH)))) {
+		scx_ops_error("dispatch kfunc called from a nested operation");
+		return false;
+	}
+
+	return true;
+}
+
+/* see SCX_CALL_OP_TASK() */
+static __always_inline bool scx_kf_allowed_on_arg_tasks(u32 mask,
+							struct task_struct *p)
+{
+	if (!scx_kf_allowed(mask))
+		return false;
+
+	if (unlikely((p != current->scx.kf_tasks[0] &&
+		      p != current->scx.kf_tasks[1]))) {
+		scx_ops_error("called on a task not being operated on");
+		return false;
+	}
+
+	return true;
+}
+
+/**
+ * nldsq_next_task - Iterate to the next task in a non-local DSQ
+ * @dsq: user dsq being interated
+ * @cur: current position, %NULL to start iteration
+ * @rev: walk backwards
+ *
+ * Returns %NULL when iteration is finished.
+ */
+static struct task_struct *nldsq_next_task(struct scx_dispatch_q *dsq,
+					   struct task_struct *cur, bool rev)
+{
+	struct list_head *list_node;
+	struct scx_dsq_list_node *dsq_lnode;
+
+	lockdep_assert_held(&dsq->lock);
+
+	if (cur)
+		list_node = &cur->scx.dsq_list.node;
+	else
+		list_node = &dsq->list;
+
+	/* find the next task, need to skip BPF iteration cursors */
+	do {
+		if (rev)
+			list_node = list_node->prev;
+		else
+			list_node = list_node->next;
+
+		if (list_node == &dsq->list)
+			return NULL;
+
+		dsq_lnode = container_of(list_node, struct scx_dsq_list_node,
+					 node);
+	} while (dsq_lnode->is_bpf_iter_cursor);
+
+	return container_of(dsq_lnode, struct task_struct, scx.dsq_list);
+}
+
+#define nldsq_for_each_task(p, dsq)						\
+	for ((p) = nldsq_next_task((dsq), NULL, false); (p);			\
+	     (p) = nldsq_next_task((dsq), (p), false))
+
+
+/*
+ * BPF DSQ iterator. Tasks in a non-local DSQ can be iterated in [reverse]
+ * dispatch order. BPF-visible iterator is opaque and larger to allow future
+ * changes without breaking backward compatibility. Can be used with
+ * bpf_for_each(). See bpf_iter_scx_dsq_*().
+ */
+enum scx_dsq_iter_flags {
+	/* iterate in the reverse dispatch order */
+	SCX_DSQ_ITER_REV		= 1U << 0,
+
+	__SCX_DSQ_ITER_ALL_FLAGS	= SCX_DSQ_ITER_REV,
+};
+
+struct bpf_iter_scx_dsq_kern {
+	struct scx_dsq_list_node	cursor;
+	struct scx_dispatch_q		*dsq;
+	u32				dsq_seq;
+	u32				flags;
+} __attribute__((aligned(8)));
+
+struct bpf_iter_scx_dsq {
+	u64				__opaque[6];
+} __attribute__((aligned(8)));
+
+
+/*
+ * SCX task iterator.
+ */
+struct scx_task_iter {
+	struct sched_ext_entity		cursor;
+	struct task_struct		*locked;
+	struct rq			*rq;
+	struct rq_flags			rf;
+};
+
+/**
+ * scx_task_iter_init - Initialize a task iterator
+ * @iter: iterator to init
+ *
+ * Initialize @iter. Must be called with scx_tasks_lock held. Once initialized,
+ * @iter must eventually be exited with scx_task_iter_exit().
+ *
+ * scx_tasks_lock may be released between this and the first next() call or
+ * between any two next() calls. If scx_tasks_lock is released between two
+ * next() calls, the caller is responsible for ensuring that the task being
+ * iterated remains accessible either through RCU read lock or obtaining a
+ * reference count.
+ *
+ * All tasks which existed when the iteration started are guaranteed to be
+ * visited as long as they still exist.
+ */
+static void scx_task_iter_init(struct scx_task_iter *iter)
+{
+	lockdep_assert_held(&scx_tasks_lock);
+
+	iter->cursor = (struct sched_ext_entity){ .flags = SCX_TASK_CURSOR };
+	list_add(&iter->cursor.tasks_node, &scx_tasks);
+	iter->locked = NULL;
+}
+
+/**
+ * scx_task_iter_rq_unlock - Unlock rq locked by a task iterator
+ * @iter: iterator to unlock rq for
+ *
+ * If @iter is in the middle of a locked iteration, it may be locking the rq of
+ * the task currently being visited. Unlock the rq if so. This function can be
+ * safely called anytime during an iteration.
+ *
+ * Returns %true if the rq @iter was locking is unlocked. %false if @iter was
+ * not locking an rq.
+ */
+static bool scx_task_iter_rq_unlock(struct scx_task_iter *iter)
+{
+	if (iter->locked) {
+		task_rq_unlock(iter->rq, iter->locked, &iter->rf);
+		iter->locked = NULL;
+		return true;
+	} else {
+		return false;
+	}
+}
+
+/**
+ * scx_task_iter_exit - Exit a task iterator
+ * @iter: iterator to exit
+ *
+ * Exit a previously initialized @iter. Must be called with scx_tasks_lock held.
+ * If the iterator holds a task's rq lock, that rq lock is released. See
+ * scx_task_iter_init() for details.
+ */
+static void scx_task_iter_exit(struct scx_task_iter *iter)
+{
+	lockdep_assert_held(&scx_tasks_lock);
+
+	scx_task_iter_rq_unlock(iter);
+	list_del_init(&iter->cursor.tasks_node);
+}
+
+/**
+ * scx_task_iter_next - Next task
+ * @iter: iterator to walk
+ *
+ * Visit the next task. See scx_task_iter_init() for details.
+ */
+static struct task_struct *scx_task_iter_next(struct scx_task_iter *iter)
+{
+	struct list_head *cursor = &iter->cursor.tasks_node;
+	struct sched_ext_entity *pos;
+
+	lockdep_assert_held(&scx_tasks_lock);
+
+	list_for_each_entry(pos, cursor, tasks_node) {
+		if (&pos->tasks_node == &scx_tasks)
+			return NULL;
+		if (!(pos->flags & SCX_TASK_CURSOR)) {
+			list_move(cursor, &pos->tasks_node);
+			return container_of(pos, struct task_struct, scx);
+		}
+	}
+
+	/* can't happen, should always terminate at scx_tasks above */
+	BUG();
+}
+
+/**
+ * scx_task_iter_next_locked - Next non-idle task with its rq locked
+ * @iter: iterator to walk
+ * @include_dead: Whether we should include dead tasks in the iteration
+ *
+ * Visit the non-idle task with its rq lock held. Allows callers to specify
+ * whether they would like to filter out dead tasks. See scx_task_iter_init()
+ * for details.
+ */
+static struct task_struct *
+scx_task_iter_next_locked(struct scx_task_iter *iter, bool include_dead)
+{
+	struct task_struct *p;
+retry:
+	scx_task_iter_rq_unlock(iter);
+
+	while ((p = scx_task_iter_next(iter))) {
+		/*
+		 * is_idle_task() tests %PF_IDLE which may not be set for CPUs
+		 * which haven't yet been onlined. Test sched_class directly.
+		 */
+		if (p->sched_class != &idle_sched_class)
+			break;
+	}
+	if (!p)
+		return NULL;
+
+	iter->rq = task_rq_lock(p, &iter->rf);
+	iter->locked = p;
+
+	/*
+	 * If we see %TASK_DEAD, @p already disabled preemption, is about to do
+	 * the final __schedule(), won't ever need to be scheduled again and can
+	 * thus be safely ignored. If we don't see %TASK_DEAD, @p can't enter
+	 * the final __schedle() while we're locking its rq and thus will stay
+	 * alive until the rq is unlocked.
+	 */
+	if (!include_dead && READ_ONCE(p->__state) == TASK_DEAD)
+		goto retry;
+
+	return p;
+}
+
+static enum scx_ops_enable_state scx_ops_enable_state(void)
+{
+	return atomic_read(&scx_ops_enable_state_var);
+}
+
+static enum scx_ops_enable_state
+scx_ops_set_enable_state(enum scx_ops_enable_state to)
+{
+	return atomic_xchg(&scx_ops_enable_state_var, to);
+}
+
+static bool scx_ops_tryset_enable_state(enum scx_ops_enable_state to,
+					enum scx_ops_enable_state from)
+{
+	int from_v = from;
+
+	return atomic_try_cmpxchg(&scx_ops_enable_state_var, &from_v, to);
+}
+
+static bool scx_ops_bypassing(void)
+{
+	return unlikely(atomic_read(&scx_ops_bypass_depth));
+}
+
+/**
+ * wait_ops_state - Busy-wait the specified ops state to end
+ * @p: target task
+ * @opss: state to wait the end of
+ *
+ * Busy-wait for @p to transition out of @opss. This can only be used when the
+ * state part of @opss is %SCX_QUEUEING or %SCX_DISPATCHING. This function also
+ * has load_acquire semantics to ensure that the caller can see the updates made
+ * in the enqueueing and dispatching paths.
+ */
+static void wait_ops_state(struct task_struct *p, unsigned long opss)
+{
+	do {
+		cpu_relax();
+	} while (atomic_long_read_acquire(&p->scx.ops_state) == opss);
+}
+
+/**
+ * ops_cpu_valid - Verify a cpu number
+ * @cpu: cpu number which came from a BPF ops
+ * @where: extra information reported on error
+ *
+ * @cpu is a cpu number which came from the BPF scheduler and can be any value.
+ * Verify that it is in range and one of the possible cpus. If invalid, trigger
+ * an ops error.
+ */
+static bool ops_cpu_valid(s32 cpu, const char *where)
+{
+	if (likely(cpu >= 0 && cpu < nr_cpu_ids && cpu_possible(cpu))) {
+		return true;
+	} else {
+		scx_ops_error("invalid CPU %d%s%s", cpu,
+			      where ? " " : "", where ?: "");
+		return false;
+	}
+}
+
+/**
+ * ops_sanitize_err - Sanitize a -errno value
+ * @ops_name: operation to blame on failure
+ * @err: -errno value to sanitize
+ *
+ * Verify @err is a valid -errno. If not, trigger scx_ops_error() and return
+ * -%EPROTO. This is necessary because returning a rogue -errno up the chain can
+ * cause misbehaviors. For an example, a large negative return from
+ * ops.init_task() triggers an oops when passed up the call chain because the
+ * value fails IS_ERR() test after being encoded with ERR_PTR() and then is
+ * handled as a pointer.
+ */
+static int ops_sanitize_err(const char *ops_name, s32 err)
+{
+	if (err < 0 && err >= -MAX_ERRNO)
+		return err;
+
+	scx_ops_error("ops.%s() returned an invalid errno %d", ops_name, err);
+	return -EPROTO;
+}
+
+static void run_deferred(struct rq *rq)
+{
+	process_ddsp_deferred_locals(rq);
+}
+
+#ifdef CONFIG_SMP
+static void deferred_bal_cb_workfn(struct rq *rq)
+{
+	run_deferred(rq);
+}
+#endif
+
+static void deferred_irq_workfn(struct irq_work *irq_work)
+{
+	struct rq *rq = container_of(irq_work, struct rq, scx.deferred_irq_work);
+
+	raw_spin_rq_lock(rq);
+	run_deferred(rq);
+	raw_spin_rq_unlock(rq);
+}
+
+/**
+ * schedule_deferred - Schedule execution of deferred actions on an rq
+ * @rq: target rq
+ *
+ * Schedule execution of deferred actions on @rq. Must be called with @rq
+ * locked. Deferred actions are executed with @rq locked but unpinned, and thus
+ * can unlock @rq to e.g. migrate tasks to other rqs.
+ */
+static void schedule_deferred(struct rq *rq)
+{
+	lockdep_assert_rq_held(rq);
+
+#ifdef CONFIG_SMP
+	/*
+	 * If in the middle of waking up a task, task_woken_scx() will be called
+	 * afterwards which will then run the deferred actions, no need to
+	 * schedule anything.
+	 */
+	if (rq->scx.flags & SCX_RQ_IN_WAKEUP)
+		return;
+
+	/*
+	 * If in balance, the balance callbacks will be called before rq lock is
+	 * released. Schedule one.
+	 */
+	if (rq->scx.flags & SCX_RQ_IN_BALANCE) {
+		queue_balance_callback(rq, &rq->scx.deferred_bal_cb,
+				       deferred_bal_cb_workfn);
+		return;
+	}
+#endif
+	/*
+	 * No scheduler hooks available. Queue an irq work. They are executed on
+	 * IRQ re-enable which may take a bit longer than the scheduler hooks.
+	 * The above WAKEUP and BALANCE paths should cover most of the cases and
+	 * the time to IRQ re-enable shouldn't be long.
+	 */
+	irq_work_queue(&rq->scx.deferred_irq_work);
+}
+
+/**
+ * touch_core_sched - Update timestamp used for core-sched task ordering
+ * @rq: rq to read clock from, must be locked
+ * @p: task to update the timestamp for
+ *
+ * Update @p->scx.core_sched_at timestamp. This is used by scx_prio_less() to
+ * implement global or local-DSQ FIFO ordering for core-sched. Should be called
+ * when a task becomes runnable and its turn on the CPU ends (e.g. slice
+ * exhaustion).
+ */
+static void touch_core_sched(struct rq *rq, struct task_struct *p)
+{
+#ifdef CONFIG_SCHED_CORE
+	/*
+	 * It's okay to update the timestamp spuriously. Use
+	 * sched_core_disabled() which is cheaper than enabled().
+	 */
+	if (!sched_core_disabled())
+		p->scx.core_sched_at = rq_clock_task(rq);
+#endif
+}
+
+/**
+ * touch_core_sched_dispatch - Update core-sched timestamp on dispatch
+ * @rq: rq to read clock from, must be locked
+ * @p: task being dispatched
+ *
+ * If the BPF scheduler implements custom core-sched ordering via
+ * ops.core_sched_before(), @p->scx.core_sched_at is used to implement FIFO
+ * ordering within each local DSQ. This function is called from dispatch paths
+ * and updates @p->scx.core_sched_at if custom core-sched ordering is in effect.
+ */
+static void touch_core_sched_dispatch(struct rq *rq, struct task_struct *p)
+{
+	lockdep_assert_rq_held(rq);
+	assert_clock_updated(rq);
+
+#ifdef CONFIG_SCHED_CORE
+	if (SCX_HAS_OP(core_sched_before))
+		touch_core_sched(rq, p);
+#endif
+}
+
+static void update_curr_scx(struct rq *rq)
+{
+	struct task_struct *curr = rq->curr;
+	u64 now = rq_clock_task(rq);
+	u64 delta_exec;
+
+	if (time_before_eq64(now, curr->se.exec_start))
+		return;
+
+	delta_exec = now - curr->se.exec_start;
+	curr->se.exec_start = now;
+	curr->se.sum_exec_runtime += delta_exec;
+	account_group_exec_runtime(curr, delta_exec);
+	cgroup_account_cputime(curr, delta_exec);
+
+	if (curr->scx.slice != SCX_SLICE_INF) {
+		curr->scx.slice -= min(curr->scx.slice, delta_exec);
+		if (!curr->scx.slice)
+			touch_core_sched(rq, curr);
+	}
+}
+
+static bool scx_dsq_priq_less(struct rb_node *node_a,
+			      const struct rb_node *node_b)
+{
+	const struct task_struct *a =
+		container_of(node_a, struct task_struct, scx.dsq_priq);
+	const struct task_struct *b =
+		container_of(node_b, struct task_struct, scx.dsq_priq);
+
+	return time_before64(a->scx.dsq_vtime, b->scx.dsq_vtime);
+}
+
+static void dsq_mod_nr(struct scx_dispatch_q *dsq, s32 delta)
+{
+	/* scx_bpf_dsq_nr_queued() reads ->nr without locking, use WRITE_ONCE() */
+	WRITE_ONCE(dsq->nr, dsq->nr + delta);
+}
+
+static void dispatch_enqueue(struct scx_dispatch_q *dsq, struct task_struct *p,
+			     u64 enq_flags)
+{
+	bool is_local = dsq->id == SCX_DSQ_LOCAL;
+
+	WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node));
+	WARN_ON_ONCE((p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) ||
+		     !RB_EMPTY_NODE(&p->scx.dsq_priq));
+
+	if (!is_local) {
+		raw_spin_lock(&dsq->lock);
+		if (unlikely(dsq->id == SCX_DSQ_INVALID)) {
+			scx_ops_error("attempting to dispatch to a destroyed dsq");
+			/* fall back to the global dsq */
+			raw_spin_unlock(&dsq->lock);
+			dsq = &scx_dsq_global;
+			raw_spin_lock(&dsq->lock);
+		}
+	}
+
+	if (unlikely((dsq->id & SCX_DSQ_FLAG_BUILTIN) &&
+		     (enq_flags & SCX_ENQ_DSQ_PRIQ))) {
+		/*
+		 * SCX_DSQ_LOCAL and SCX_DSQ_GLOBAL DSQs always consume from
+		 * their FIFO queues. To avoid confusion and accidentally
+		 * starving vtime-dispatched tasks by FIFO-dispatched tasks, we
+		 * disallow any internal DSQ from doing vtime ordering of
+		 * tasks.
+		 */
+		scx_ops_error("cannot use vtime ordering for built-in DSQs");
+		enq_flags &= ~SCX_ENQ_DSQ_PRIQ;
+	}
+
+	if (enq_flags & SCX_ENQ_DSQ_PRIQ) {
+		struct rb_node *rbp;
+
+		/*
+		 * A PRIQ DSQ shouldn't be using FIFO enqueueing. As tasks are
+		 * linked to both the rbtree and list on PRIQs, this can only be
+		 * tested easily when adding the first task.
+		 */
+		if (unlikely(RB_EMPTY_ROOT(&dsq->priq) &&
+			     nldsq_next_task(dsq, NULL, false)))
+			scx_ops_error("DSQ ID 0x%016llx already had FIFO-enqueued tasks",
+				      dsq->id);
+
+		p->scx.dsq_flags |= SCX_TASK_DSQ_ON_PRIQ;
+		rb_add(&p->scx.dsq_priq, &dsq->priq, scx_dsq_priq_less);
+
+		/*
+		 * Find the previous task and insert after it on the list so
+		 * that @dsq->list is vtime ordered.
+		 */
+		rbp = rb_prev(&p->scx.dsq_priq);
+		if (rbp) {
+			struct task_struct *prev =
+				container_of(rbp, struct task_struct,
+					     scx.dsq_priq);
+			list_add(&p->scx.dsq_list.node, &prev->scx.dsq_list.node);
+		} else {
+			list_add(&p->scx.dsq_list.node, &dsq->list);
+		}
+	} else {
+		/* a FIFO DSQ shouldn't be using PRIQ enqueuing */
+		if (unlikely(!RB_EMPTY_ROOT(&dsq->priq)))
+			scx_ops_error("DSQ ID 0x%016llx already had PRIQ-enqueued tasks",
+				      dsq->id);
+
+		if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT))
+			list_add(&p->scx.dsq_list.node, &dsq->list);
+		else
+			list_add_tail(&p->scx.dsq_list.node, &dsq->list);
+	}
+
+	/* seq records the order tasks are queued, used by BPF DSQ iterator */
+	dsq->seq++;
+	p->scx.dsq_seq = dsq->seq;
+
+	dsq_mod_nr(dsq, 1);
+	p->scx.dsq = dsq;
+
+	/*
+	 * scx.ddsp_dsq_id and scx.ddsp_enq_flags are only relevant on the
+	 * direct dispatch path, but we clear them here because the direct
+	 * dispatch verdict may be overridden on the enqueue path during e.g.
+	 * bypass.
+	 */
+	p->scx.ddsp_dsq_id = SCX_DSQ_INVALID;
+	p->scx.ddsp_enq_flags = 0;
+
+	/*
+	 * We're transitioning out of QUEUEING or DISPATCHING. store_release to
+	 * match waiters' load_acquire.
+	 */
+	if (enq_flags & SCX_ENQ_CLEAR_OPSS)
+		atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE);
+
+	if (is_local) {
+		struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
+		bool preempt = false;
+
+		if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&
+		    rq->curr->sched_class == &ext_sched_class) {
+			rq->curr->scx.slice = 0;
+			preempt = true;
+		}
+
+		if (preempt || sched_class_above(&ext_sched_class,
+						 rq->curr->sched_class))
+			resched_curr(rq);
+	} else {
+		raw_spin_unlock(&dsq->lock);
+	}
+}
+
+static void task_unlink_from_dsq(struct task_struct *p,
+				 struct scx_dispatch_q *dsq)
+{
+	if (p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) {
+		rb_erase(&p->scx.dsq_priq, &dsq->priq);
+		RB_CLEAR_NODE(&p->scx.dsq_priq);
+		p->scx.dsq_flags &= ~SCX_TASK_DSQ_ON_PRIQ;
+	}
+
+	list_del_init(&p->scx.dsq_list.node);
+}
+
+static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
+{
+	struct scx_dispatch_q *dsq = p->scx.dsq;
+	bool is_local = dsq == &rq->scx.local_dsq;
+
+	if (!dsq) {
+		/*
+		 * If !dsq && on-list, @p is on @rq's ddsp_deferred_locals.
+		 * Unlinking is all that's needed to cancel.
+		 */
+		if (unlikely(!list_empty(&p->scx.dsq_list.node)))
+			list_del_init(&p->scx.dsq_list.node);
+
+		/*
+		 * When dispatching directly from the BPF scheduler to a local
+		 * DSQ, the task isn't associated with any DSQ but
+		 * @p->scx.holding_cpu may be set under the protection of
+		 * %SCX_OPSS_DISPATCHING.
+		 */
+		if (p->scx.holding_cpu >= 0)
+			p->scx.holding_cpu = -1;
+
+		return;
+	}
+
+	if (!is_local)
+		raw_spin_lock(&dsq->lock);
+
+	/*
+	 * Now that we hold @dsq->lock, @p->holding_cpu and @p->scx.dsq_* can't
+	 * change underneath us.
+	*/
+	if (p->scx.holding_cpu < 0) {
+		/* @p must still be on @dsq, dequeue */
+		WARN_ON_ONCE(list_empty(&p->scx.dsq_list.node));
+		task_unlink_from_dsq(p, dsq);
+		dsq_mod_nr(dsq, -1);
+	} else {
+		/*
+		 * We're racing against dispatch_to_local_dsq() which already
+		 * removed @p from @dsq and set @p->scx.holding_cpu. Clear the
+		 * holding_cpu which tells dispatch_to_local_dsq() that it lost
+		 * the race.
+		 */
+		WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node));
+		p->scx.holding_cpu = -1;
+	}
+	p->scx.dsq = NULL;
+
+	if (!is_local)
+		raw_spin_unlock(&dsq->lock);
+}
+
+static struct scx_dispatch_q *find_user_dsq(u64 dsq_id)
+{
+	return rhashtable_lookup_fast(&dsq_hash, &dsq_id, dsq_hash_params);
+}
+
+static struct scx_dispatch_q *find_non_local_dsq(u64 dsq_id)
+{
+	lockdep_assert(rcu_read_lock_any_held());
+
+	if (dsq_id == SCX_DSQ_GLOBAL)
+		return &scx_dsq_global;
+	else
+		return find_user_dsq(dsq_id);
+}
+
+static struct scx_dispatch_q *find_dsq_for_dispatch(struct rq *rq, u64 dsq_id,
+						    struct task_struct *p)
+{
+	struct scx_dispatch_q *dsq;
+
+	if (dsq_id == SCX_DSQ_LOCAL)
+		return &rq->scx.local_dsq;
+
+	dsq = find_non_local_dsq(dsq_id);
+	if (unlikely(!dsq)) {
+		scx_ops_error("non-existent DSQ 0x%llx for %s[%d]",
+			      dsq_id, p->comm, p->pid);
+		return &scx_dsq_global;
+	}
+
+	return dsq;
+}
+
+static void mark_direct_dispatch(struct task_struct *ddsp_task,
+				 struct task_struct *p, u64 dsq_id,
+				 u64 enq_flags)
+{
+	/*
+	 * Mark that dispatch already happened from ops.select_cpu() or
+	 * ops.enqueue() by spoiling direct_dispatch_task with a non-NULL value
+	 * which can never match a valid task pointer.
+	 */
+	__this_cpu_write(direct_dispatch_task, ERR_PTR(-ESRCH));
+
+	/* @p must match the task on the enqueue path */
+	if (unlikely(p != ddsp_task)) {
+		if (IS_ERR(ddsp_task))
+			scx_ops_error("%s[%d] already direct-dispatched",
+				      p->comm, p->pid);
+		else
+			scx_ops_error("scheduling for %s[%d] but trying to direct-dispatch %s[%d]",
+				      ddsp_task->comm, ddsp_task->pid,
+				      p->comm, p->pid);
+		return;
+	}
+
+	WARN_ON_ONCE(p->scx.ddsp_dsq_id != SCX_DSQ_INVALID);
+	WARN_ON_ONCE(p->scx.ddsp_enq_flags);
+
+	p->scx.ddsp_dsq_id = dsq_id;
+	p->scx.ddsp_enq_flags = enq_flags;
+}
+
+static void direct_dispatch(struct task_struct *p, u64 enq_flags)
+{
+	struct rq *rq = task_rq(p);
+	struct scx_dispatch_q *dsq;
+	u64 dsq_id = p->scx.ddsp_dsq_id;
+
+	touch_core_sched_dispatch(rq, p);
+
+	p->scx.ddsp_enq_flags |= enq_flags;
+
+	/*
+	 * We are in the enqueue path with @rq locked and pinned, and thus can't
+	 * double lock a remote rq and enqueue to its local DSQ. For
+	 * DSQ_LOCAL_ON verdicts targeting the local DSQ of a remote CPU, defer
+	 * the enqueue so that it's executed when @rq can be unlocked.
+	 */
+	if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) {
+		s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK;
+		unsigned long opss;
+
+		if (cpu == cpu_of(rq)) {
+			dsq_id = SCX_DSQ_LOCAL;
+			goto dispatch;
+		}
+
+		opss = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_STATE_MASK;
+
+		switch (opss & SCX_OPSS_STATE_MASK) {
+		case SCX_OPSS_NONE:
+			break;
+		case SCX_OPSS_QUEUEING:
+			/*
+			 * As @p was never passed to the BPF side, _release is
+			 * not strictly necessary. Still do it for consistency.
+			 */
+			atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE);
+			break;
+		default:
+			WARN_ONCE(true, "sched_ext: %s[%d] has invalid ops state 0x%lx in direct_dispatch()",
+				  p->comm, p->pid, opss);
+			atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE);
+			break;
+		}
+
+		WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node));
+		list_add_tail(&p->scx.dsq_list.node,
+			      &rq->scx.ddsp_deferred_locals);
+		schedule_deferred(rq);
+		return;
+	}
+
+dispatch:
+	dsq = find_dsq_for_dispatch(rq, dsq_id, p);
+	dispatch_enqueue(dsq, p, p->scx.ddsp_enq_flags | SCX_ENQ_CLEAR_OPSS);
+}
+
+static bool scx_rq_online(struct rq *rq)
+{
+	return likely(rq->scx.flags & SCX_RQ_ONLINE);
+}
+
+static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
+			    int sticky_cpu)
+{
+	struct task_struct **ddsp_taskp;
+	unsigned long qseq;
+
+	WARN_ON_ONCE(!(p->scx.flags & SCX_TASK_QUEUED));
+
+	/* rq migration */
+	if (sticky_cpu == cpu_of(rq))
+		goto local_norefill;
+
+	/*
+	 * If !scx_rq_online(), we already told the BPF scheduler that the CPU
+	 * is offline and are just running the hotplug path. Don't bother the
+	 * BPF scheduler.
+	 */
+	if (!scx_rq_online(rq))
+		goto local;
+
+	if (scx_ops_bypassing()) {
+		if (enq_flags & SCX_ENQ_LAST)
+			goto local;
+		else
+			goto global;
+	}
+
+	if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID)
+		goto direct;
+
+	/* see %SCX_OPS_ENQ_EXITING */
+	if (!static_branch_unlikely(&scx_ops_enq_exiting) &&
+	    unlikely(p->flags & PF_EXITING))
+		goto local;
+
+	/* see %SCX_OPS_ENQ_LAST */
+	if (!static_branch_unlikely(&scx_ops_enq_last) &&
+	    (enq_flags & SCX_ENQ_LAST))
+		goto local;
+
+	if (!SCX_HAS_OP(enqueue))
+		goto global;
+
+	/* DSQ bypass didn't trigger, enqueue on the BPF scheduler */
+	qseq = rq->scx.ops_qseq++ << SCX_OPSS_QSEQ_SHIFT;
+
+	WARN_ON_ONCE(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE);
+	atomic_long_set(&p->scx.ops_state, SCX_OPSS_QUEUEING | qseq);
+
+	ddsp_taskp = this_cpu_ptr(&direct_dispatch_task);
+	WARN_ON_ONCE(*ddsp_taskp);
+	*ddsp_taskp = p;
+
+	SCX_CALL_OP_TASK(SCX_KF_ENQUEUE, enqueue, p, enq_flags);
+
+	*ddsp_taskp = NULL;
+	if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID)
+		goto direct;
+
+	/*
+	 * If not directly dispatched, QUEUEING isn't clear yet and dispatch or
+	 * dequeue may be waiting. The store_release matches their load_acquire.
+	 */
+	atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_QUEUED | qseq);
+	return;
+
+direct:
+	direct_dispatch(p, enq_flags);
+	return;
+
+local:
+	/*
+	 * For task-ordering, slice refill must be treated as implying the end
+	 * of the current slice. Otherwise, the longer @p stays on the CPU, the
+	 * higher priority it becomes from scx_prio_less()'s POV.
+	 */
+	touch_core_sched(rq, p);
+	p->scx.slice = SCX_SLICE_DFL;
+local_norefill:
+	dispatch_enqueue(&rq->scx.local_dsq, p, enq_flags);
+	return;
+
+global:
+	touch_core_sched(rq, p);	/* see the comment in local: */
+	p->scx.slice = SCX_SLICE_DFL;
+	dispatch_enqueue(&scx_dsq_global, p, enq_flags);
+}
+
+static bool task_runnable(const struct task_struct *p)
+{
+	return !list_empty(&p->scx.runnable_node);
+}
+
+static void set_task_runnable(struct rq *rq, struct task_struct *p)
+{
+	lockdep_assert_rq_held(rq);
+
+	if (p->scx.flags & SCX_TASK_RESET_RUNNABLE_AT) {
+		p->scx.runnable_at = jiffies;
+		p->scx.flags &= ~SCX_TASK_RESET_RUNNABLE_AT;
+	}
+
+	/*
+	 * list_add_tail() must be used. scx_ops_bypass() depends on tasks being
+	 * appened to the runnable_list.
+	 */
+	list_add_tail(&p->scx.runnable_node, &rq->scx.runnable_list);
+}
+
+static void clr_task_runnable(struct task_struct *p, bool reset_runnable_at)
+{
+	list_del_init(&p->scx.runnable_node);
+	if (reset_runnable_at)
+		p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT;
+}
+
+static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int enq_flags)
+{
+	int sticky_cpu = p->scx.sticky_cpu;
+
+	if (enq_flags & ENQUEUE_WAKEUP)
+		rq->scx.flags |= SCX_RQ_IN_WAKEUP;
+
+	enq_flags |= rq->scx.extra_enq_flags;
+
+	if (sticky_cpu >= 0)
+		p->scx.sticky_cpu = -1;
+
+	/*
+	 * Restoring a running task will be immediately followed by
+	 * set_next_task_scx() which expects the task to not be on the BPF
+	 * scheduler as tasks can only start running through local DSQs. Force
+	 * direct-dispatch into the local DSQ by setting the sticky_cpu.
+	 */
+	if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p))
+		sticky_cpu = cpu_of(rq);
+
+	if (p->scx.flags & SCX_TASK_QUEUED) {
+		WARN_ON_ONCE(!task_runnable(p));
+		goto out;
+	}
+
+	set_task_runnable(rq, p);
+	p->scx.flags |= SCX_TASK_QUEUED;
+	rq->scx.nr_running++;
+	add_nr_running(rq, 1);
+
+	if (SCX_HAS_OP(runnable))
+		SCX_CALL_OP_TASK(SCX_KF_REST, runnable, p, enq_flags);
+
+	if (enq_flags & SCX_ENQ_WAKEUP)
+		touch_core_sched(rq, p);
+
+	do_enqueue_task(rq, p, enq_flags, sticky_cpu);
+out:
+	rq->scx.flags &= ~SCX_RQ_IN_WAKEUP;
+}
+
+static void ops_dequeue(struct task_struct *p, u64 deq_flags)
+{
+	unsigned long opss;
+
+	/* dequeue is always temporary, don't reset runnable_at */
+	clr_task_runnable(p, false);
+
+	/* acquire ensures that we see the preceding updates on QUEUED */
+	opss = atomic_long_read_acquire(&p->scx.ops_state);
+
+	switch (opss & SCX_OPSS_STATE_MASK) {
+	case SCX_OPSS_NONE:
+		break;
+	case SCX_OPSS_QUEUEING:
+		/*
+		 * QUEUEING is started and finished while holding @p's rq lock.
+		 * As we're holding the rq lock now, we shouldn't see QUEUEING.
+		 */
+		BUG();
+	case SCX_OPSS_QUEUED:
+		if (SCX_HAS_OP(dequeue))
+			SCX_CALL_OP_TASK(SCX_KF_REST, dequeue, p, deq_flags);
+
+		if (atomic_long_try_cmpxchg(&p->scx.ops_state, &opss,
+					    SCX_OPSS_NONE))
+			break;
+		fallthrough;
+	case SCX_OPSS_DISPATCHING:
+		/*
+		 * If @p is being dispatched from the BPF scheduler to a DSQ,
+		 * wait for the transfer to complete so that @p doesn't get
+		 * added to its DSQ after dequeueing is complete.
+		 *
+		 * As we're waiting on DISPATCHING with the rq locked, the
+		 * dispatching side shouldn't try to lock the rq while
+		 * DISPATCHING is set. See dispatch_to_local_dsq().
+		 *
+		 * DISPATCHING shouldn't have qseq set and control can reach
+		 * here with NONE @opss from the above QUEUED case block.
+		 * Explicitly wait on %SCX_OPSS_DISPATCHING instead of @opss.
+		 */
+		wait_ops_state(p, SCX_OPSS_DISPATCHING);
+		BUG_ON(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE);
+		break;
+	}
+}
+
+static void dequeue_task_scx(struct rq *rq, struct task_struct *p, int deq_flags)
+{
+	if (!(p->scx.flags & SCX_TASK_QUEUED)) {
+		WARN_ON_ONCE(task_runnable(p));
+		return;
+	}
+
+	ops_dequeue(p, deq_flags);
+
+	/*
+	 * A currently running task which is going off @rq first gets dequeued
+	 * and then stops running. As we want running <-> stopping transitions
+	 * to be contained within runnable <-> quiescent transitions, trigger
+	 * ->stopping() early here instead of in put_prev_task_scx().
+	 *
+	 * @p may go through multiple stopping <-> running transitions between
+	 * here and put_prev_task_scx() if task attribute changes occur while
+	 * balance_scx() leaves @rq unlocked. However, they don't contain any
+	 * information meaningful to the BPF scheduler and can be suppressed by
+	 * skipping the callbacks if the task is !QUEUED.
+	 */
+	if (SCX_HAS_OP(stopping) && task_current(rq, p)) {
+		update_curr_scx(rq);
+		SCX_CALL_OP_TASK(SCX_KF_REST, stopping, p, false);
+	}
+
+	if (SCX_HAS_OP(quiescent))
+		SCX_CALL_OP_TASK(SCX_KF_REST, quiescent, p, deq_flags);
+
+	if (deq_flags & SCX_DEQ_SLEEP)
+		p->scx.flags |= SCX_TASK_DEQD_FOR_SLEEP;
+	else
+		p->scx.flags &= ~SCX_TASK_DEQD_FOR_SLEEP;
+
+	p->scx.flags &= ~SCX_TASK_QUEUED;
+	rq->scx.nr_running--;
+	sub_nr_running(rq, 1);
+
+	dispatch_dequeue(rq, p);
+}
+
+static void yield_task_scx(struct rq *rq)
+{
+	struct task_struct *p = rq->curr;
+
+	if (SCX_HAS_OP(yield))
+		SCX_CALL_OP_2TASKS_RET(SCX_KF_REST, yield, p, NULL);
+	else
+		p->scx.slice = 0;
+}
+
+static bool yield_to_task_scx(struct rq *rq, struct task_struct *to)
+{
+	struct task_struct *from = rq->curr;
+
+	if (SCX_HAS_OP(yield))
+		return SCX_CALL_OP_2TASKS_RET(SCX_KF_REST, yield, from, to);
+	else
+		return false;
+}
+
+#ifdef CONFIG_SMP
+/**
+ * move_task_to_local_dsq - Move a task from a different rq to a local DSQ
+ * @rq: rq to move the task into, currently locked
+ * @p: task to move
+ * @enq_flags: %SCX_ENQ_*
+ *
+ * Move @p which is currently on a different rq to @rq's local DSQ. The caller
+ * must:
+ *
+ * 1. Start with exclusive access to @p either through its DSQ lock or
+ *    %SCX_OPSS_DISPATCHING flag.
+ *
+ * 2. Set @p->scx.holding_cpu to raw_smp_processor_id().
+ *
+ * 3. Remember task_rq(@p). Release the exclusive access so that we don't
+ *    deadlock with dequeue.
+ *
+ * 4. Lock @rq and the task_rq from #3.
+ *
+ * 5. Call this function.
+ *
+ * Returns %true if @p was successfully moved. %false after racing dequeue and
+ * losing.
+ */
+static bool move_task_to_local_dsq(struct rq *rq, struct task_struct *p,
+				   u64 enq_flags)
+{
+	struct rq *task_rq;
+
+	lockdep_assert_rq_held(rq);
+
+	/*
+	 * If dequeue got to @p while we were trying to lock both rq's, it'd
+	 * have cleared @p->scx.holding_cpu to -1. While other cpus may have
+	 * updated it to different values afterwards, as this operation can't be
+	 * preempted or recurse, @p->scx.holding_cpu can never become
+	 * raw_smp_processor_id() again before we're done. Thus, we can tell
+	 * whether we lost to dequeue by testing whether @p->scx.holding_cpu is
+	 * still raw_smp_processor_id().
+	 *
+	 * See dispatch_dequeue() for the counterpart.
+	 */
+	if (unlikely(p->scx.holding_cpu != raw_smp_processor_id()))
+		return false;
+
+	/* @p->rq couldn't have changed if we're still the holding cpu */
+	task_rq = task_rq(p);
+	lockdep_assert_rq_held(task_rq);
+
+	WARN_ON_ONCE(!cpumask_test_cpu(cpu_of(rq), p->cpus_ptr));
+	deactivate_task(task_rq, p, 0);
+	set_task_cpu(p, cpu_of(rq));
+	p->scx.sticky_cpu = cpu_of(rq);
+
+	/*
+	 * We want to pass scx-specific enq_flags but activate_task() will
+	 * truncate the upper 32 bit. As we own @rq, we can pass them through
+	 * @rq->scx.extra_enq_flags instead.
+	 */
+	WARN_ON_ONCE(rq->scx.extra_enq_flags);
+	rq->scx.extra_enq_flags = enq_flags;
+	activate_task(rq, p, 0);
+	rq->scx.extra_enq_flags = 0;
+
+	return true;
+}
+
+/**
+ * dispatch_to_local_dsq_lock - Ensure source and destination rq's are locked
+ * @rq: current rq which is locked
+ * @src_rq: rq to move task from
+ * @dst_rq: rq to move task to
+ *
+ * We're holding @rq lock and trying to dispatch a task from @src_rq to
+ * @dst_rq's local DSQ and thus need to lock both @src_rq and @dst_rq. Whether
+ * @rq stays locked isn't important as long as the state is restored after
+ * dispatch_to_local_dsq_unlock().
+ */
+static void dispatch_to_local_dsq_lock(struct rq *rq, struct rq *src_rq,
+				       struct rq *dst_rq)
+{
+	if (src_rq == dst_rq) {
+		raw_spin_rq_unlock(rq);
+		raw_spin_rq_lock(dst_rq);
+	} else if (rq == src_rq) {
+		double_lock_balance(rq, dst_rq);
+	} else if (rq == dst_rq) {
+		double_lock_balance(rq, src_rq);
+	} else {
+		raw_spin_rq_unlock(rq);
+		double_rq_lock(src_rq, dst_rq);
+	}
+}
+
+/**
+ * dispatch_to_local_dsq_unlock - Undo dispatch_to_local_dsq_lock()
+ * @rq: current rq which is locked
+ * @src_rq: rq to move task from
+ * @dst_rq: rq to move task to
+ *
+ * Unlock @src_rq and @dst_rq and ensure that @rq is locked on return.
+ */
+static void dispatch_to_local_dsq_unlock(struct rq *rq, struct rq *src_rq,
+					 struct rq *dst_rq)
+{
+	if (src_rq == dst_rq) {
+		raw_spin_rq_unlock(dst_rq);
+		raw_spin_rq_lock(rq);
+	} else if (rq == src_rq) {
+		double_unlock_balance(rq, dst_rq);
+	} else if (rq == dst_rq) {
+		double_unlock_balance(rq, src_rq);
+	} else {
+		double_rq_unlock(src_rq, dst_rq);
+		raw_spin_rq_lock(rq);
+	}
+}
+#endif	/* CONFIG_SMP */
+
+static void consume_local_task(struct rq *rq, struct scx_dispatch_q *dsq,
+			       struct task_struct *p)
+{
+	lockdep_assert_held(&dsq->lock);	/* released on return */
+
+	/* @dsq is locked and @p is on this rq */
+	WARN_ON_ONCE(p->scx.holding_cpu >= 0);
+	task_unlink_from_dsq(p, dsq);
+	list_add_tail(&p->scx.dsq_list.node, &rq->scx.local_dsq.list);
+	dsq_mod_nr(dsq, -1);
+	dsq_mod_nr(&rq->scx.local_dsq, 1);
+	p->scx.dsq = &rq->scx.local_dsq;
+	raw_spin_unlock(&dsq->lock);
+}
+
+#ifdef CONFIG_SMP
+/*
+ * Similar to kernel/sched/core.c::is_cpu_allowed() but we're testing whether @p
+ * can be pulled to @rq.
+ */
+static bool task_can_run_on_remote_rq(struct task_struct *p, struct rq *rq)
+{
+	int cpu = cpu_of(rq);
+
+	if (!cpumask_test_cpu(cpu, p->cpus_ptr))
+		return false;
+	if (unlikely(is_migration_disabled(p)))
+		return false;
+	if (!(p->flags & PF_KTHREAD) && unlikely(!task_cpu_possible(cpu, p)))
+		return false;
+	if (!scx_rq_online(rq))
+		return false;
+	return true;
+}
+
+static bool consume_remote_task(struct rq *rq, struct scx_dispatch_q *dsq,
+				struct task_struct *p, struct rq *task_rq)
+{
+	bool moved = false;
+
+	lockdep_assert_held(&dsq->lock);	/* released on return */
+
+	/*
+	 * @dsq is locked and @p is on a remote rq. @p is currently protected by
+	 * @dsq->lock. We want to pull @p to @rq but may deadlock if we grab
+	 * @task_rq while holding @dsq and @rq locks. As dequeue can't drop the
+	 * rq lock or fail, do a little dancing from our side. See
+	 * move_task_to_local_dsq().
+	 */
+	WARN_ON_ONCE(p->scx.holding_cpu >= 0);
+	task_unlink_from_dsq(p, dsq);
+	dsq_mod_nr(dsq, -1);
+	p->scx.holding_cpu = raw_smp_processor_id();
+	raw_spin_unlock(&dsq->lock);
+
+	double_lock_balance(rq, task_rq);
+
+	moved = move_task_to_local_dsq(rq, p, 0);
+
+	double_unlock_balance(rq, task_rq);
+
+	return moved;
+}
+#else	/* CONFIG_SMP */
+static bool task_can_run_on_remote_rq(struct task_struct *p, struct rq *rq) { return false; }
+static bool consume_remote_task(struct rq *rq, struct scx_dispatch_q *dsq,
+				struct task_struct *p, struct rq *task_rq) { return false; }
+#endif	/* CONFIG_SMP */
+
+static bool consume_dispatch_q(struct rq *rq, struct scx_dispatch_q *dsq)
+{
+	struct task_struct *p;
+retry:
+	/*
+	 * The caller can't expect to successfully consume a task if the task's
+	 * addition to @dsq isn't guaranteed to be visible somehow. Test
+	 * @dsq->list without locking and skip if it seems empty.
+	 */
+	if (list_empty(&dsq->list))
+		return false;
+
+	raw_spin_lock(&dsq->lock);
+
+	nldsq_for_each_task(p, dsq) {
+		struct rq *task_rq = task_rq(p);
+
+		if (rq == task_rq) {
+			consume_local_task(rq, dsq, p);
+			return true;
+		}
+
+		if (task_can_run_on_remote_rq(p, rq)) {
+			if (likely(consume_remote_task(rq, dsq, p, task_rq)))
+				return true;
+			goto retry;
+		}
+	}
+
+	raw_spin_unlock(&dsq->lock);
+	return false;
+}
+
+enum dispatch_to_local_dsq_ret {
+	DTL_DISPATCHED,		/* successfully dispatched */
+	DTL_LOST,		/* lost race to dequeue */
+	DTL_NOT_LOCAL,		/* destination is not a local DSQ */
+	DTL_INVALID,		/* invalid local dsq_id */
+};
+
+/**
+ * dispatch_to_local_dsq - Dispatch a task to a local dsq
+ * @rq: current rq which is locked
+ * @dsq_id: destination dsq ID
+ * @p: task to dispatch
+ * @enq_flags: %SCX_ENQ_*
+ *
+ * We're holding @rq lock and want to dispatch @p to the local DSQ identified by
+ * @dsq_id. This function performs all the synchronization dancing needed
+ * because local DSQs are protected with rq locks.
+ *
+ * The caller must have exclusive ownership of @p (e.g. through
+ * %SCX_OPSS_DISPATCHING).
+ */
+static enum dispatch_to_local_dsq_ret
+dispatch_to_local_dsq(struct rq *rq, u64 dsq_id, struct task_struct *p,
+		      u64 enq_flags)
+{
+	struct rq *src_rq = task_rq(p);
+	struct rq *dst_rq;
+
+	/*
+	 * We're synchronized against dequeue through DISPATCHING. As @p can't
+	 * be dequeued, its task_rq and cpus_allowed are stable too.
+	 */
+	if (dsq_id == SCX_DSQ_LOCAL) {
+		dst_rq = rq;
+	} else if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) {
+		s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK;
+
+		if (!ops_cpu_valid(cpu, "in SCX_DSQ_LOCAL_ON dispatch verdict"))
+			return DTL_INVALID;
+		dst_rq = cpu_rq(cpu);
+	} else {
+		return DTL_NOT_LOCAL;
+	}
+
+	/* if dispatching to @rq that @p is already on, no lock dancing needed */
+	if (rq == src_rq && rq == dst_rq) {
+		dispatch_enqueue(&dst_rq->scx.local_dsq, p,
+				 enq_flags | SCX_ENQ_CLEAR_OPSS);
+		return DTL_DISPATCHED;
+	}
+
+#ifdef CONFIG_SMP
+	if (cpumask_test_cpu(cpu_of(dst_rq), p->cpus_ptr)) {
+		struct rq *locked_dst_rq = dst_rq;
+		bool dsp;
+
+		/*
+		 * @p is on a possibly remote @src_rq which we need to lock to
+		 * move the task. If dequeue is in progress, it'd be locking
+		 * @src_rq and waiting on DISPATCHING, so we can't grab @src_rq
+		 * lock while holding DISPATCHING.
+		 *
+		 * As DISPATCHING guarantees that @p is wholly ours, we can
+		 * pretend that we're moving from a DSQ and use the same
+		 * mechanism - mark the task under transfer with holding_cpu,
+		 * release DISPATCHING and then follow the same protocol.
+		 */
+		p->scx.holding_cpu = raw_smp_processor_id();
+
+		/* store_release ensures that dequeue sees the above */
+		atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE);
+
+		dispatch_to_local_dsq_lock(rq, src_rq, locked_dst_rq);
+
+		/*
+		 * We don't require the BPF scheduler to avoid dispatching to
+		 * offline CPUs mostly for convenience but also because CPUs can
+		 * go offline between scx_bpf_dispatch() calls and here. If @p
+		 * is destined to an offline CPU, queue it on its current CPU
+		 * instead, which should always be safe. As this is an allowed
+		 * behavior, don't trigger an ops error.
+		 */
+		if (!scx_rq_online(dst_rq))
+			dst_rq = src_rq;
+
+		if (src_rq == dst_rq) {
+			/*
+			 * As @p is staying on the same rq, there's no need to
+			 * go through the full deactivate/activate cycle.
+			 * Optimize by abbreviating the operations in
+			 * move_task_to_local_dsq().
+			 */
+			dsp = p->scx.holding_cpu == raw_smp_processor_id();
+			if (likely(dsp)) {
+				p->scx.holding_cpu = -1;
+				dispatch_enqueue(&dst_rq->scx.local_dsq, p,
+						 enq_flags);
+			}
+		} else {
+			dsp = move_task_to_local_dsq(dst_rq, p, enq_flags);
+		}
+
+		/* if the destination CPU is idle, wake it up */
+		if (dsp && sched_class_above(p->sched_class,
+					     dst_rq->curr->sched_class))
+			resched_curr(dst_rq);
+
+		dispatch_to_local_dsq_unlock(rq, src_rq, locked_dst_rq);
+
+		return dsp ? DTL_DISPATCHED : DTL_LOST;
+	}
+#endif	/* CONFIG_SMP */
+
+	scx_ops_error("SCX_DSQ_LOCAL[_ON] verdict target cpu %d not allowed for %s[%d]",
+		      cpu_of(dst_rq), p->comm, p->pid);
+	return DTL_INVALID;
+}
+
+/**
+ * finish_dispatch - Asynchronously finish dispatching a task
+ * @rq: current rq which is locked
+ * @p: task to finish dispatching
+ * @qseq_at_dispatch: qseq when @p started getting dispatched
+ * @dsq_id: destination DSQ ID
+ * @enq_flags: %SCX_ENQ_*
+ *
+ * Dispatching to local DSQs may need to wait for queueing to complete or
+ * require rq lock dancing. As we don't wanna do either while inside
+ * ops.dispatch() to avoid locking order inversion, we split dispatching into
+ * two parts. scx_bpf_dispatch() which is called by ops.dispatch() records the
+ * task and its qseq. Once ops.dispatch() returns, this function is called to
+ * finish up.
+ *
+ * There is no guarantee that @p is still valid for dispatching or even that it
+ * was valid in the first place. Make sure that the task is still owned by the
+ * BPF scheduler and claim the ownership before dispatching.
+ */
+static void finish_dispatch(struct rq *rq, struct task_struct *p,
+			    unsigned long qseq_at_dispatch,
+			    u64 dsq_id, u64 enq_flags)
+{
+	struct scx_dispatch_q *dsq;
+	unsigned long opss;
+
+	touch_core_sched_dispatch(rq, p);
+retry:
+	/*
+	 * No need for _acquire here. @p is accessed only after a successful
+	 * try_cmpxchg to DISPATCHING.
+	 */
+	opss = atomic_long_read(&p->scx.ops_state);
+
+	switch (opss & SCX_OPSS_STATE_MASK) {
+	case SCX_OPSS_DISPATCHING:
+	case SCX_OPSS_NONE:
+		/* someone else already got to it */
+		return;
+	case SCX_OPSS_QUEUED:
+		/*
+		 * If qseq doesn't match, @p has gone through at least one
+		 * dispatch/dequeue and re-enqueue cycle between
+		 * scx_bpf_dispatch() and here and we have no claim on it.
+		 */
+		if ((opss & SCX_OPSS_QSEQ_MASK) != qseq_at_dispatch)
+			return;
+
+		/*
+		 * While we know @p is accessible, we don't yet have a claim on
+		 * it - the BPF scheduler is allowed to dispatch tasks
+		 * spuriously and there can be a racing dequeue attempt. Let's
+		 * claim @p by atomically transitioning it from QUEUED to
+		 * DISPATCHING.
+		 */
+		if (likely(atomic_long_try_cmpxchg(&p->scx.ops_state, &opss,
+						   SCX_OPSS_DISPATCHING)))
+			break;
+		goto retry;
+	case SCX_OPSS_QUEUEING:
+		/*
+		 * do_enqueue_task() is in the process of transferring the task
+		 * to the BPF scheduler while holding @p's rq lock. As we aren't
+		 * holding any kernel or BPF resource that the enqueue path may
+		 * depend upon, it's safe to wait.
+		 */
+		wait_ops_state(p, opss);
+		goto retry;
+	}
+
+	BUG_ON(!(p->scx.flags & SCX_TASK_QUEUED));
+
+	switch (dispatch_to_local_dsq(rq, dsq_id, p, enq_flags)) {
+	case DTL_DISPATCHED:
+		break;
+	case DTL_LOST:
+		break;
+	case DTL_INVALID:
+		dsq_id = SCX_DSQ_GLOBAL;
+		fallthrough;
+	case DTL_NOT_LOCAL:
+		dsq = find_dsq_for_dispatch(cpu_rq(raw_smp_processor_id()),
+					    dsq_id, p);
+		dispatch_enqueue(dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
+		break;
+	}
+}
+
+static void flush_dispatch_buf(struct rq *rq)
+{
+	struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
+	u32 u;
+
+	for (u = 0; u < dspc->cursor; u++) {
+		struct scx_dsp_buf_ent *ent = &dspc->buf[u];
+
+		finish_dispatch(rq, ent->task, ent->qseq, ent->dsq_id,
+				ent->enq_flags);
+	}
+
+	dspc->nr_tasks += dspc->cursor;
+	dspc->cursor = 0;
+}
+
+static int balance_one(struct rq *rq, struct task_struct *prev, bool local)
+{
+	struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
+	bool prev_on_scx = prev->sched_class == &ext_sched_class;
+	int nr_loops = SCX_DSP_MAX_LOOPS;
+	bool has_tasks = false;
+
+	lockdep_assert_rq_held(rq);
+	rq->scx.flags |= SCX_RQ_IN_BALANCE;
+
+	if (static_branch_unlikely(&scx_ops_cpu_preempt) &&
+	    unlikely(rq->scx.cpu_released)) {
+		/*
+		 * If the previous sched_class for the current CPU was not SCX,
+		 * notify the BPF scheduler that it again has control of the
+		 * core. This callback complements ->cpu_release(), which is
+		 * emitted in scx_next_task_picked().
+		 */
+		if (SCX_HAS_OP(cpu_acquire))
+			SCX_CALL_OP(0, cpu_acquire, cpu_of(rq), NULL);
+		rq->scx.cpu_released = false;
+	}
+
+	if (prev_on_scx) {
+		WARN_ON_ONCE(local && (prev->scx.flags & SCX_TASK_BAL_KEEP));
+		update_curr_scx(rq);
+
+		/*
+		 * If @prev is runnable & has slice left, it has priority and
+		 * fetching more just increases latency for the fetched tasks.
+		 * Tell put_prev_task_scx() to put @prev on local_dsq. If the
+		 * BPF scheduler wants to handle this explicitly, it should
+		 * implement ->cpu_released().
+		 *
+		 * See scx_ops_disable_workfn() for the explanation on the
+		 * bypassing test.
+		 *
+		 * When balancing a remote CPU for core-sched, there won't be a
+		 * following put_prev_task_scx() call and we don't own
+		 * %SCX_TASK_BAL_KEEP. Instead, pick_task_scx() will test the
+		 * same conditions later and pick @rq->curr accordingly.
+		 */
+		if ((prev->scx.flags & SCX_TASK_QUEUED) &&
+		    prev->scx.slice && !scx_ops_bypassing()) {
+			if (local)
+				prev->scx.flags |= SCX_TASK_BAL_KEEP;
+			goto has_tasks;
+		}
+	}
+
+	/* if there already are tasks to run, nothing to do */
+	if (rq->scx.local_dsq.nr)
+		goto has_tasks;
+
+	if (consume_dispatch_q(rq, &scx_dsq_global))
+		goto has_tasks;
+
+	if (!SCX_HAS_OP(dispatch) || scx_ops_bypassing() || !scx_rq_online(rq))
+		goto out;
+
+	dspc->rq = rq;
+
+	/*
+	 * The dispatch loop. Because flush_dispatch_buf() may drop the rq lock,
+	 * the local DSQ might still end up empty after a successful
+	 * ops.dispatch(). If the local DSQ is empty even after ops.dispatch()
+	 * produced some tasks, retry. The BPF scheduler may depend on this
+	 * looping behavior to simplify its implementation.
+	 */
+	do {
+		dspc->nr_tasks = 0;
+
+		SCX_CALL_OP(SCX_KF_DISPATCH, dispatch, cpu_of(rq),
+			    prev_on_scx ? prev : NULL);
+
+		flush_dispatch_buf(rq);
+
+		if (rq->scx.local_dsq.nr)
+			goto has_tasks;
+		if (consume_dispatch_q(rq, &scx_dsq_global))
+			goto has_tasks;
+
+		/*
+		 * ops.dispatch() can trap us in this loop by repeatedly
+		 * dispatching ineligible tasks. Break out once in a while to
+		 * allow the watchdog to run. As IRQ can't be enabled in
+		 * balance(), we want to complete this scheduling cycle and then
+		 * start a new one. IOW, we want to call resched_curr() on the
+		 * next, most likely idle, task, not the current one. Use
+		 * scx_bpf_kick_cpu() for deferred kicking.
+		 */
+		if (unlikely(!--nr_loops)) {
+			scx_bpf_kick_cpu(cpu_of(rq), 0);
+			break;
+		}
+	} while (dspc->nr_tasks);
+
+	goto out;
+
+has_tasks:
+	has_tasks = true;
+out:
+	rq->scx.flags &= ~SCX_RQ_IN_BALANCE;
+	return has_tasks;
+}
+
+#ifdef CONFIG_SMP
+static int balance_scx(struct rq *rq, struct task_struct *prev,
+		       struct rq_flags *rf)
+{
+	int ret;
+
+	rq_unpin_lock(rq, rf);
+
+	ret = balance_one(rq, prev, true);
+
+#ifdef CONFIG_SCHED_SMT
+	/*
+	 * When core-sched is enabled, this ops.balance() call will be followed
+	 * by put_prev_scx() and pick_task_scx() on this CPU and pick_task_scx()
+	 * on the SMT siblings. Balance the siblings too.
+	 */
+	if (sched_core_enabled(rq)) {
+		const struct cpumask *smt_mask = cpu_smt_mask(cpu_of(rq));
+		int scpu;
+
+		for_each_cpu_andnot(scpu, smt_mask, cpumask_of(cpu_of(rq))) {
+			struct rq *srq = cpu_rq(scpu);
+			struct task_struct *sprev = srq->curr;
+
+			WARN_ON_ONCE(__rq_lockp(rq) != __rq_lockp(srq));
+			update_rq_clock(srq);
+			balance_one(srq, sprev, false);
+		}
+	}
+#endif
+	rq_repin_lock(rq, rf);
+
+	return ret;
+}
+#endif
+
+static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first)
+{
+	if (p->scx.flags & SCX_TASK_QUEUED) {
+		/*
+		 * Core-sched might decide to execute @p before it is
+		 * dispatched. Call ops_dequeue() to notify the BPF scheduler.
+		 */
+		ops_dequeue(p, SCX_DEQ_CORE_SCHED_EXEC);
+		dispatch_dequeue(rq, p);
+	}
+
+	p->se.exec_start = rq_clock_task(rq);
+
+	/* see dequeue_task_scx() on why we skip when !QUEUED */
+	if (SCX_HAS_OP(running) && (p->scx.flags & SCX_TASK_QUEUED))
+		SCX_CALL_OP_TASK(SCX_KF_REST, running, p);
+
+	clr_task_runnable(p, true);
+
+	/*
+	 * @p is getting newly scheduled or got kicked after someone updated its
+	 * slice. Refresh whether tick can be stopped. See scx_can_stop_tick().
+	 */
+	if ((p->scx.slice == SCX_SLICE_INF) !=
+	    (bool)(rq->scx.flags & SCX_RQ_CAN_STOP_TICK)) {
+		if (p->scx.slice == SCX_SLICE_INF)
+			rq->scx.flags |= SCX_RQ_CAN_STOP_TICK;
+		else
+			rq->scx.flags &= ~SCX_RQ_CAN_STOP_TICK;
+
+		sched_update_tick_dependency(rq);
+
+		/*
+		 * For now, let's refresh the load_avgs just when transitioning
+		 * in and out of nohz. In the future, we might want to add a
+		 * mechanism which calls the following periodically on
+		 * tick-stopped CPUs.
+		 */
+		update_other_load_avgs(rq);
+	}
+}
+
+static void process_ddsp_deferred_locals(struct rq *rq)
+{
+	struct task_struct *p, *tmp;
+
+	lockdep_assert_rq_held(rq);
+
+	/*
+	 * Now that @rq can be unlocked, execute the deferred enqueueing of
+	 * tasks directly dispatched to the local DSQs of other CPUs. See
+	 * direct_dispatch().
+	 */
+	list_for_each_entry_safe(p, tmp, &rq->scx.ddsp_deferred_locals,
+				 scx.dsq_list.node) {
+		s32 ret;
+
+		list_del_init(&p->scx.dsq_list.node);
+
+		ret = dispatch_to_local_dsq(rq, p->scx.ddsp_dsq_id, p,
+					    p->scx.ddsp_enq_flags);
+		WARN_ON_ONCE(ret == DTL_NOT_LOCAL);
+	}
+}
+
+static void put_prev_task_scx(struct rq *rq, struct task_struct *p)
+{
+#ifndef CONFIG_SMP
+	/*
+	 * UP workaround.
+	 *
+	 * Because SCX may transfer tasks across CPUs during dispatch, dispatch
+	 * is performed from its balance operation which isn't called in UP.
+	 * Let's work around by calling it from the operations which come right
+	 * after.
+	 *
+	 * 1. If the prev task is on SCX, pick_next_task() calls
+	 *    .put_prev_task() right after. As .put_prev_task() is also called
+	 *    from other places, we need to distinguish the calls which can be
+	 *    done by looking at the previous task's state - if still queued or
+	 *    dequeued with %SCX_DEQ_SLEEP, the caller must be pick_next_task().
+	 *    This case is handled here.
+	 *
+	 * 2. If the prev task is not on SCX, the first following call into SCX
+	 *    will be .pick_next_task(), which is covered by calling
+	 *    balance_scx() from pick_next_task_scx().
+	 *
+	 * Note that we can't merge the first case into the second as
+	 * balance_scx() must be called before the previous SCX task goes
+	 * through put_prev_task_scx().
+	 *
+         * @rq is pinned and can't be unlocked. As UP doesn't transfer tasks
+         * around, balance_one() doesn't need to.
+	 */
+	if (p->scx.flags & (SCX_TASK_QUEUED | SCX_TASK_DEQD_FOR_SLEEP))
+		balance_one(rq, p, true);
+#endif
+
+	update_curr_scx(rq);
+
+	/* see dequeue_task_scx() on why we skip when !QUEUED */
+	if (SCX_HAS_OP(stopping) && (p->scx.flags & SCX_TASK_QUEUED))
+		SCX_CALL_OP_TASK(SCX_KF_REST, stopping, p, true);
+
+	/*
+	 * If we're being called from put_prev_task_balance(), balance_scx() may
+	 * have decided that @p should keep running.
+	 */
+	if (p->scx.flags & SCX_TASK_BAL_KEEP) {
+		p->scx.flags &= ~SCX_TASK_BAL_KEEP;
+		set_task_runnable(rq, p);
+		dispatch_enqueue(&rq->scx.local_dsq, p, SCX_ENQ_HEAD);
+		return;
+	}
+
+	if (p->scx.flags & SCX_TASK_QUEUED) {
+		set_task_runnable(rq, p);
+
+		/*
+		 * If @p has slice left and balance_scx() didn't tag it for
+		 * keeping, @p is getting preempted by a higher priority
+		 * scheduler class or core-sched forcing a different task. Leave
+		 * it at the head of the local DSQ.
+		 */
+		if (p->scx.slice && !scx_ops_bypassing()) {
+			dispatch_enqueue(&rq->scx.local_dsq, p, SCX_ENQ_HEAD);
+			return;
+		}
+
+		/*
+		 * If we're in the pick_next_task path, balance_scx() should
+		 * have already populated the local DSQ if there are any other
+		 * available tasks. If empty, tell ops.enqueue() that @p is the
+		 * only one available for this cpu. ops.enqueue() should put it
+		 * on the local DSQ so that the subsequent pick_next_task_scx()
+		 * can find the task unless it wants to trigger a separate
+		 * follow-up scheduling event.
+		 */
+		if (list_empty(&rq->scx.local_dsq.list))
+			do_enqueue_task(rq, p, SCX_ENQ_LAST, -1);
+		else
+			do_enqueue_task(rq, p, 0, -1);
+	}
+}
+
+static struct task_struct *first_local_task(struct rq *rq)
+{
+	return list_first_entry_or_null(&rq->scx.local_dsq.list,
+					struct task_struct, scx.dsq_list.node);
+}
+
+static struct task_struct *pick_next_task_scx(struct rq *rq)
+{
+	struct task_struct *p;
+
+#ifndef CONFIG_SMP
+	/* UP workaround - see the comment at the head of put_prev_task_scx() */
+	if (unlikely(rq->curr->sched_class != &ext_sched_class))
+		balance_one(rq, rq->curr, true);
+#endif
+
+	p = first_local_task(rq);
+	if (!p)
+		return NULL;
+
+	set_next_task_scx(rq, p, true);
+
+	if (unlikely(!p->scx.slice)) {
+		if (!scx_ops_bypassing() && !scx_warned_zero_slice) {
+			printk_deferred(KERN_WARNING "sched_ext: %s[%d] has zero slice in pick_next_task_scx()\n",
+					p->comm, p->pid);
+			scx_warned_zero_slice = true;
+		}
+		p->scx.slice = SCX_SLICE_DFL;
+	}
+
+	return p;
+}
+
+#ifdef CONFIG_SCHED_CORE
+/**
+ * scx_prio_less - Task ordering for core-sched
+ * @a: task A
+ * @b: task B
+ *
+ * Core-sched is implemented as an additional scheduling layer on top of the
+ * usual sched_class'es and needs to find out the expected task ordering. For
+ * SCX, core-sched calls this function to interrogate the task ordering.
+ *
+ * Unless overridden by ops.core_sched_before(), @p->scx.core_sched_at is used
+ * to implement the default task ordering. The older the timestamp, the higher
+ * prority the task - the global FIFO ordering matching the default scheduling
+ * behavior.
+ *
+ * When ops.core_sched_before() is enabled, @p->scx.core_sched_at is used to
+ * implement FIFO ordering within each local DSQ. See pick_task_scx().
+ */
+bool scx_prio_less(const struct task_struct *a, const struct task_struct *b,
+		   bool in_fi)
+{
+	/*
+	 * The const qualifiers are dropped from task_struct pointers when
+	 * calling ops.core_sched_before(). Accesses are controlled by the
+	 * verifier.
+	 */
+	if (SCX_HAS_OP(core_sched_before) && !scx_ops_bypassing())
+		return SCX_CALL_OP_2TASKS_RET(SCX_KF_REST, core_sched_before,
+					      (struct task_struct *)a,
+					      (struct task_struct *)b);
+	else
+		return time_after64(a->scx.core_sched_at, b->scx.core_sched_at);
+}
+
+/**
+ * pick_task_scx - Pick a candidate task for core-sched
+ * @rq: rq to pick the candidate task from
+ *
+ * Core-sched calls this function on each SMT sibling to determine the next
+ * tasks to run on the SMT siblings. balance_one() has been called on all
+ * siblings and put_prev_task_scx() has been called only for the current CPU.
+ *
+ * As put_prev_task_scx() hasn't been called on remote CPUs, we can't just look
+ * at the first task in the local dsq. @rq->curr has to be considered explicitly
+ * to mimic %SCX_TASK_BAL_KEEP.
+ */
+static struct task_struct *pick_task_scx(struct rq *rq)
+{
+	struct task_struct *curr = rq->curr;
+	struct task_struct *first = first_local_task(rq);
+
+	if (curr->scx.flags & SCX_TASK_QUEUED) {
+		/* is curr the only runnable task? */
+		if (!first)
+			return curr;
+
+		/*
+		 * Does curr trump first? We can always go by core_sched_at for
+		 * this comparison as it represents global FIFO ordering when
+		 * the default core-sched ordering is used and local-DSQ FIFO
+		 * ordering otherwise.
+		 *
+		 * We can have a task with an earlier timestamp on the DSQ. For
+		 * example, when a current task is preempted by a sibling
+		 * picking a different cookie, the task would be requeued at the
+		 * head of the local DSQ with an earlier timestamp than the
+		 * core-sched picked next task. Besides, the BPF scheduler may
+		 * dispatch any tasks to the local DSQ anytime.
+		 */
+		if (curr->scx.slice && time_before64(curr->scx.core_sched_at,
+						     first->scx.core_sched_at))
+			return curr;
+	}
+
+	return first;	/* this may be %NULL */
+}
+#endif	/* CONFIG_SCHED_CORE */
+
+static enum scx_cpu_preempt_reason
+preempt_reason_from_class(const struct sched_class *class)
+{
+#ifdef CONFIG_SMP
+	if (class == &stop_sched_class)
+		return SCX_CPU_PREEMPT_STOP;
+#endif
+	if (class == &dl_sched_class)
+		return SCX_CPU_PREEMPT_DL;
+	if (class == &rt_sched_class)
+		return SCX_CPU_PREEMPT_RT;
+	return SCX_CPU_PREEMPT_UNKNOWN;
+}
+
+static void switch_class_scx(struct rq *rq, struct task_struct *next)
+{
+	const struct sched_class *next_class = next->sched_class;
+
+	if (!scx_enabled())
+		return;
+#ifdef CONFIG_SMP
+	/*
+	 * Pairs with the smp_load_acquire() issued by a CPU in
+	 * kick_cpus_irq_workfn() who is waiting for this CPU to perform a
+	 * resched.
+	 */
+	smp_store_release(&rq->scx.pnt_seq, rq->scx.pnt_seq + 1);
+#endif
+	if (!static_branch_unlikely(&scx_ops_cpu_preempt))
+		return;
+
+	/*
+	 * The callback is conceptually meant to convey that the CPU is no
+	 * longer under the control of SCX. Therefore, don't invoke the callback
+	 * if the next class is below SCX (in which case the BPF scheduler has
+	 * actively decided not to schedule any tasks on the CPU).
+	 */
+	if (sched_class_above(&ext_sched_class, next_class))
+		return;
+
+	/*
+	 * At this point we know that SCX was preempted by a higher priority
+	 * sched_class, so invoke the ->cpu_release() callback if we have not
+	 * done so already. We only send the callback once between SCX being
+	 * preempted, and it regaining control of the CPU.
+	 *
+	 * ->cpu_release() complements ->cpu_acquire(), which is emitted the
+	 *  next time that balance_scx() is invoked.
+	 */
+	if (!rq->scx.cpu_released) {
+		if (SCX_HAS_OP(cpu_release)) {
+			struct scx_cpu_release_args args = {
+				.reason = preempt_reason_from_class(next_class),
+				.task = next,
+			};
+
+			SCX_CALL_OP(SCX_KF_CPU_RELEASE,
+				    cpu_release, cpu_of(rq), &args);
+		}
+		rq->scx.cpu_released = true;
+	}
+}
+
+#ifdef CONFIG_SMP
+
+static bool test_and_clear_cpu_idle(int cpu)
+{
+#ifdef CONFIG_SCHED_SMT
+	/*
+	 * SMT mask should be cleared whether we can claim @cpu or not. The SMT
+	 * cluster is not wholly idle either way. This also prevents
+	 * scx_pick_idle_cpu() from getting caught in an infinite loop.
+	 */
+	if (sched_smt_active()) {
+		const struct cpumask *smt = cpu_smt_mask(cpu);
+
+		/*
+		 * If offline, @cpu is not its own sibling and
+		 * scx_pick_idle_cpu() can get caught in an infinite loop as
+		 * @cpu is never cleared from idle_masks.smt. Ensure that @cpu
+		 * is eventually cleared.
+		 */
+		if (cpumask_intersects(smt, idle_masks.smt))
+			cpumask_andnot(idle_masks.smt, idle_masks.smt, smt);
+		else if (cpumask_test_cpu(cpu, idle_masks.smt))
+			__cpumask_clear_cpu(cpu, idle_masks.smt);
+	}
+#endif
+	return cpumask_test_and_clear_cpu(cpu, idle_masks.cpu);
+}
+
+static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags)
+{
+	int cpu;
+
+retry:
+	if (sched_smt_active()) {
+		cpu = cpumask_any_and_distribute(idle_masks.smt, cpus_allowed);
+		if (cpu < nr_cpu_ids)
+			goto found;
+
+		if (flags & SCX_PICK_IDLE_CORE)
+			return -EBUSY;
+	}
+
+	cpu = cpumask_any_and_distribute(idle_masks.cpu, cpus_allowed);
+	if (cpu >= nr_cpu_ids)
+		return -EBUSY;
+
+found:
+	if (test_and_clear_cpu_idle(cpu))
+		return cpu;
+	else
+		goto retry;
+}
+
+static s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
+			      u64 wake_flags, bool *found)
+{
+	s32 cpu;
+
+	*found = false;
+
+	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
+		scx_ops_error("built-in idle tracking is disabled");
+		return prev_cpu;
+	}
+
+	/*
+	 * If WAKE_SYNC, the waker's local DSQ is empty, and the system is
+	 * under utilized, wake up @p to the local DSQ of the waker. Checking
+	 * only for an empty local DSQ is insufficient as it could give the
+	 * wakee an unfair advantage when the system is oversaturated.
+	 * Checking only for the presence of idle CPUs is also insufficient as
+	 * the local DSQ of the waker could have tasks piled up on it even if
+	 * there is an idle core elsewhere on the system.
+	 */
+	cpu = smp_processor_id();
+	if ((wake_flags & SCX_WAKE_SYNC) && p->nr_cpus_allowed > 1 &&
+	    !cpumask_empty(idle_masks.cpu) && !(current->flags & PF_EXITING) &&
+	    cpu_rq(cpu)->scx.local_dsq.nr == 0) {
+		if (cpumask_test_cpu(cpu, p->cpus_ptr))
+			goto cpu_found;
+	}
+
+	if (p->nr_cpus_allowed == 1) {
+		if (test_and_clear_cpu_idle(prev_cpu)) {
+			cpu = prev_cpu;
+			goto cpu_found;
+		} else {
+			return prev_cpu;
+		}
+	}
+
+	/*
+	 * If CPU has SMT, any wholly idle CPU is likely a better pick than
+	 * partially idle @prev_cpu.
+	 */
+	if (sched_smt_active()) {
+		if (cpumask_test_cpu(prev_cpu, idle_masks.smt) &&
+		    test_and_clear_cpu_idle(prev_cpu)) {
+			cpu = prev_cpu;
+			goto cpu_found;
+		}
+
+		cpu = scx_pick_idle_cpu(p->cpus_ptr, SCX_PICK_IDLE_CORE);
+		if (cpu >= 0)
+			goto cpu_found;
+	}
+
+	if (test_and_clear_cpu_idle(prev_cpu)) {
+		cpu = prev_cpu;
+		goto cpu_found;
+	}
+
+	cpu = scx_pick_idle_cpu(p->cpus_ptr, 0);
+	if (cpu >= 0)
+		goto cpu_found;
+
+	return prev_cpu;
+
+cpu_found:
+	*found = true;
+	return cpu;
+}
+
+static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flags)
+{
+	/*
+	 * sched_exec() calls with %WF_EXEC when @p is about to exec(2) as it
+	 * can be a good migration opportunity with low cache and memory
+	 * footprint. Returning a CPU different than @prev_cpu triggers
+	 * immediate rq migration. However, for SCX, as the current rq
+	 * association doesn't dictate where the task is going to run, this
+	 * doesn't fit well. If necessary, we can later add a dedicated method
+	 * which can decide to preempt self to force it through the regular
+	 * scheduling path.
+	 */
+	if (unlikely(wake_flags & WF_EXEC))
+		return prev_cpu;
+
+	if (SCX_HAS_OP(select_cpu)) {
+		s32 cpu;
+		struct task_struct **ddsp_taskp;
+
+		ddsp_taskp = this_cpu_ptr(&direct_dispatch_task);
+		WARN_ON_ONCE(*ddsp_taskp);
+		*ddsp_taskp = p;
+
+		cpu = SCX_CALL_OP_TASK_RET(SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU,
+					   select_cpu, p, prev_cpu, wake_flags);
+		*ddsp_taskp = NULL;
+		if (ops_cpu_valid(cpu, "from ops.select_cpu()"))
+			return cpu;
+		else
+			return prev_cpu;
+	} else {
+		bool found;
+		s32 cpu;
+
+		cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, &found);
+		if (found) {
+			p->scx.slice = SCX_SLICE_DFL;
+			p->scx.ddsp_dsq_id = SCX_DSQ_LOCAL;
+		}
+		return cpu;
+	}
+}
+
+static void task_woken_scx(struct rq *rq, struct task_struct *p)
+{
+	run_deferred(rq);
+}
+
+static void set_cpus_allowed_scx(struct task_struct *p,
+				 struct affinity_context *ac)
+{
+	set_cpus_allowed_common(p, ac);
+
+	/*
+	 * The effective cpumask is stored in @p->cpus_ptr which may temporarily
+	 * differ from the configured one in @p->cpus_mask. Always tell the bpf
+	 * scheduler the effective one.
+	 *
+	 * Fine-grained memory write control is enforced by BPF making the const
+	 * designation pointless. Cast it away when calling the operation.
+	 */
+	if (SCX_HAS_OP(set_cpumask))
+		SCX_CALL_OP_TASK(SCX_KF_REST, set_cpumask, p,
+				 (struct cpumask *)p->cpus_ptr);
+}
+
+static void reset_idle_masks(void)
+{
+	/*
+	 * Consider all online cpus idle. Should converge to the actual state
+	 * quickly.
+	 */
+	cpumask_copy(idle_masks.cpu, cpu_online_mask);
+	cpumask_copy(idle_masks.smt, cpu_online_mask);
+}
+
+void __scx_update_idle(struct rq *rq, bool idle)
+{
+	int cpu = cpu_of(rq);
+
+	if (SCX_HAS_OP(update_idle)) {
+		SCX_CALL_OP(SCX_KF_REST, update_idle, cpu_of(rq), idle);
+		if (!static_branch_unlikely(&scx_builtin_idle_enabled))
+			return;
+	}
+
+	if (idle)
+		cpumask_set_cpu(cpu, idle_masks.cpu);
+	else
+		cpumask_clear_cpu(cpu, idle_masks.cpu);
+
+#ifdef CONFIG_SCHED_SMT
+	if (sched_smt_active()) {
+		const struct cpumask *smt = cpu_smt_mask(cpu);
+
+		if (idle) {
+			/*
+			 * idle_masks.smt handling is racy but that's fine as
+			 * it's only for optimization and self-correcting.
+			 */
+			for_each_cpu(cpu, smt) {
+				if (!cpumask_test_cpu(cpu, idle_masks.cpu))
+					return;
+			}
+			cpumask_or(idle_masks.smt, idle_masks.smt, smt);
+		} else {
+			cpumask_andnot(idle_masks.smt, idle_masks.smt, smt);
+		}
+	}
+#endif
+}
+
+static void handle_hotplug(struct rq *rq, bool online)
+{
+	int cpu = cpu_of(rq);
+
+	atomic_long_inc(&scx_hotplug_seq);
+
+	if (online && SCX_HAS_OP(cpu_online))
+		SCX_CALL_OP(SCX_KF_SLEEPABLE, cpu_online, cpu);
+	else if (!online && SCX_HAS_OP(cpu_offline))
+		SCX_CALL_OP(SCX_KF_SLEEPABLE, cpu_offline, cpu);
+	else
+		scx_ops_exit(SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG,
+			     "cpu %d going %s, exiting scheduler", cpu,
+			     online ? "online" : "offline");
+}
+
+void scx_rq_activate(struct rq *rq)
+{
+	handle_hotplug(rq, true);
+}
+
+void scx_rq_deactivate(struct rq *rq)
+{
+	handle_hotplug(rq, false);
+}
+
+static void rq_online_scx(struct rq *rq)
+{
+	rq->scx.flags |= SCX_RQ_ONLINE;
+}
+
+static void rq_offline_scx(struct rq *rq)
+{
+	rq->scx.flags &= ~SCX_RQ_ONLINE;
+}
+
+#else	/* CONFIG_SMP */
+
+static bool test_and_clear_cpu_idle(int cpu) { return false; }
+static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, u64 flags) { return -EBUSY; }
+static void reset_idle_masks(void) {}
+
+#endif	/* CONFIG_SMP */
+
+static bool check_rq_for_timeouts(struct rq *rq)
+{
+	struct task_struct *p;
+	struct rq_flags rf;
+	bool timed_out = false;
+
+	rq_lock_irqsave(rq, &rf);
+	list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) {
+		unsigned long last_runnable = p->scx.runnable_at;
+
+		if (unlikely(time_after(jiffies,
+					last_runnable + scx_watchdog_timeout))) {
+			u32 dur_ms = jiffies_to_msecs(jiffies - last_runnable);
+
+			scx_ops_error_kind(SCX_EXIT_ERROR_STALL,
+					   "%s[%d] failed to run for %u.%03us",
+					   p->comm, p->pid,
+					   dur_ms / 1000, dur_ms % 1000);
+			timed_out = true;
+			break;
+		}
+	}
+	rq_unlock_irqrestore(rq, &rf);
+
+	return timed_out;
+}
+
+static void scx_watchdog_workfn(struct work_struct *work)
+{
+	int cpu;
+
+	WRITE_ONCE(scx_watchdog_timestamp, jiffies);
+
+	for_each_online_cpu(cpu) {
+		if (unlikely(check_rq_for_timeouts(cpu_rq(cpu))))
+			break;
+
+		cond_resched();
+	}
+	queue_delayed_work(system_unbound_wq, to_delayed_work(work),
+			   scx_watchdog_timeout / 2);
+}
+
+void scx_tick(struct rq *rq)
+{
+	unsigned long last_check;
+
+	if (!scx_enabled())
+		return;
+
+	last_check = READ_ONCE(scx_watchdog_timestamp);
+	if (unlikely(time_after(jiffies,
+				last_check + READ_ONCE(scx_watchdog_timeout)))) {
+		u32 dur_ms = jiffies_to_msecs(jiffies - last_check);
+
+		scx_ops_error_kind(SCX_EXIT_ERROR_STALL,
+				   "watchdog failed to check in for %u.%03us",
+				   dur_ms / 1000, dur_ms % 1000);
+	}
+
+	update_other_load_avgs(rq);
+}
+
+static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued)
+{
+	update_curr_scx(rq);
+
+	/*
+	 * While disabling, always resched and refresh core-sched timestamp as
+	 * we can't trust the slice management or ops.core_sched_before().
+	 */
+	if (scx_ops_bypassing()) {
+		curr->scx.slice = 0;
+		touch_core_sched(rq, curr);
+	} else if (SCX_HAS_OP(tick)) {
+		SCX_CALL_OP(SCX_KF_REST, tick, curr);
+	}
+
+	if (!curr->scx.slice)
+		resched_curr(rq);
+}
+
+static enum scx_task_state scx_get_task_state(const struct task_struct *p)
+{
+	return (p->scx.flags & SCX_TASK_STATE_MASK) >> SCX_TASK_STATE_SHIFT;
+}
+
+static void scx_set_task_state(struct task_struct *p, enum scx_task_state state)
+{
+	enum scx_task_state prev_state = scx_get_task_state(p);
+	bool warn = false;
+
+	BUILD_BUG_ON(SCX_TASK_NR_STATES > (1 << SCX_TASK_STATE_BITS));
+
+	switch (state) {
+	case SCX_TASK_NONE:
+		break;
+	case SCX_TASK_INIT:
+		warn = prev_state != SCX_TASK_NONE;
+		break;
+	case SCX_TASK_READY:
+		warn = prev_state == SCX_TASK_NONE;
+		break;
+	case SCX_TASK_ENABLED:
+		warn = prev_state != SCX_TASK_READY;
+		break;
+	default:
+		warn = true;
+		return;
+	}
+
+	WARN_ONCE(warn, "sched_ext: Invalid task state transition %d -> %d for %s[%d]",
+		  prev_state, state, p->comm, p->pid);
+
+	p->scx.flags &= ~SCX_TASK_STATE_MASK;
+	p->scx.flags |= state << SCX_TASK_STATE_SHIFT;
+}
+
+static int scx_ops_init_task(struct task_struct *p, struct task_group *tg, bool fork)
+{
+	int ret;
+
+	p->scx.disallow = false;
+
+	if (SCX_HAS_OP(init_task)) {
+		struct scx_init_task_args args = {
+			.fork = fork,
+		};
+
+		ret = SCX_CALL_OP_RET(SCX_KF_SLEEPABLE, init_task, p, &args);
+		if (unlikely(ret)) {
+			ret = ops_sanitize_err("init_task", ret);
+			return ret;
+		}
+	}
+
+	scx_set_task_state(p, SCX_TASK_INIT);
+
+	if (p->scx.disallow) {
+		struct rq *rq;
+		struct rq_flags rf;
+
+		rq = task_rq_lock(p, &rf);
+
+		/*
+		 * We're either in fork or load path and @p->policy will be
+		 * applied right after. Reverting @p->policy here and rejecting
+		 * %SCHED_EXT transitions from scx_check_setscheduler()
+		 * guarantees that if ops.init_task() sets @p->disallow, @p can
+		 * never be in SCX.
+		 */
+		if (p->policy == SCHED_EXT) {
+			p->policy = SCHED_NORMAL;
+			atomic_long_inc(&scx_nr_rejected);
+		}
+
+		task_rq_unlock(rq, p, &rf);
+	}
+
+	p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT;
+	return 0;
+}
+
+static void scx_ops_enable_task(struct task_struct *p)
+{
+	u32 weight;
+
+	lockdep_assert_rq_held(task_rq(p));
+
+	/*
+	 * Set the weight before calling ops.enable() so that the scheduler
+	 * doesn't see a stale value if they inspect the task struct.
+	 */
+	if (task_has_idle_policy(p))
+		weight = WEIGHT_IDLEPRIO;
+	else
+		weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO];
+
+	p->scx.weight = sched_weight_to_cgroup(weight);
+
+	if (SCX_HAS_OP(enable))
+		SCX_CALL_OP_TASK(SCX_KF_REST, enable, p);
+	scx_set_task_state(p, SCX_TASK_ENABLED);
+
+	if (SCX_HAS_OP(set_weight))
+		SCX_CALL_OP(SCX_KF_REST, set_weight, p, p->scx.weight);
+}
+
+static void scx_ops_disable_task(struct task_struct *p)
+{
+	lockdep_assert_rq_held(task_rq(p));
+	WARN_ON_ONCE(scx_get_task_state(p) != SCX_TASK_ENABLED);
+
+	if (SCX_HAS_OP(disable))
+		SCX_CALL_OP(SCX_KF_REST, disable, p);
+	scx_set_task_state(p, SCX_TASK_READY);
+}
+
+static void scx_ops_exit_task(struct task_struct *p)
+{
+	struct scx_exit_task_args args = {
+		.cancelled = false,
+	};
+
+	lockdep_assert_rq_held(task_rq(p));
+
+	switch (scx_get_task_state(p)) {
+	case SCX_TASK_NONE:
+		return;
+	case SCX_TASK_INIT:
+		args.cancelled = true;
+		break;
+	case SCX_TASK_READY:
+		break;
+	case SCX_TASK_ENABLED:
+		scx_ops_disable_task(p);
+		break;
+	default:
+		WARN_ON_ONCE(true);
+		return;
+	}
+
+	if (SCX_HAS_OP(exit_task))
+		SCX_CALL_OP(SCX_KF_REST, exit_task, p, &args);
+	scx_set_task_state(p, SCX_TASK_NONE);
+}
+
+void init_scx_entity(struct sched_ext_entity *scx)
+{
+	/*
+	 * init_idle() calls this function again after fork sequence is
+	 * complete. Don't touch ->tasks_node as it's already linked.
+	 */
+	memset(scx, 0, offsetof(struct sched_ext_entity, tasks_node));
+
+	INIT_LIST_HEAD(&scx->dsq_list.node);
+	RB_CLEAR_NODE(&scx->dsq_priq);
+	scx->sticky_cpu = -1;
+	scx->holding_cpu = -1;
+	INIT_LIST_HEAD(&scx->runnable_node);
+	scx->runnable_at = jiffies;
+	scx->ddsp_dsq_id = SCX_DSQ_INVALID;
+	scx->slice = SCX_SLICE_DFL;
+}
+
+void scx_pre_fork(struct task_struct *p)
+{
+	/*
+	 * BPF scheduler enable/disable paths want to be able to iterate and
+	 * update all tasks which can become complex when racing forks. As
+	 * enable/disable are very cold paths, let's use a percpu_rwsem to
+	 * exclude forks.
+	 */
+	percpu_down_read(&scx_fork_rwsem);
+}
+
+int scx_fork(struct task_struct *p)
+{
+	percpu_rwsem_assert_held(&scx_fork_rwsem);
+
+	if (scx_enabled())
+		return scx_ops_init_task(p, task_group(p), true);
+	else
+		return 0;
+}
+
+void scx_post_fork(struct task_struct *p)
+{
+	if (scx_enabled()) {
+		scx_set_task_state(p, SCX_TASK_READY);
+
+		/*
+		 * Enable the task immediately if it's running on sched_ext.
+		 * Otherwise, it'll be enabled in switching_to_scx() if and
+		 * when it's ever configured to run with a SCHED_EXT policy.
+		 */
+		if (p->sched_class == &ext_sched_class) {
+			struct rq_flags rf;
+			struct rq *rq;
+
+			rq = task_rq_lock(p, &rf);
+			scx_ops_enable_task(p);
+			task_rq_unlock(rq, p, &rf);
+		}
+	}
+
+	spin_lock_irq(&scx_tasks_lock);
+	list_add_tail(&p->scx.tasks_node, &scx_tasks);
+	spin_unlock_irq(&scx_tasks_lock);
+
+	percpu_up_read(&scx_fork_rwsem);
+}
+
+void scx_cancel_fork(struct task_struct *p)
+{
+	if (scx_enabled()) {
+		struct rq *rq;
+		struct rq_flags rf;
+
+		rq = task_rq_lock(p, &rf);
+		WARN_ON_ONCE(scx_get_task_state(p) >= SCX_TASK_READY);
+		scx_ops_exit_task(p);
+		task_rq_unlock(rq, p, &rf);
+	}
+
+	percpu_up_read(&scx_fork_rwsem);
+}
+
+void sched_ext_free(struct task_struct *p)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&scx_tasks_lock, flags);
+	list_del_init(&p->scx.tasks_node);
+	spin_unlock_irqrestore(&scx_tasks_lock, flags);
+
+	/*
+	 * @p is off scx_tasks and wholly ours. scx_ops_enable()'s READY ->
+	 * ENABLED transitions can't race us. Disable ops for @p.
+	 */
+	if (scx_get_task_state(p) != SCX_TASK_NONE) {
+		struct rq_flags rf;
+		struct rq *rq;
+
+		rq = task_rq_lock(p, &rf);
+		scx_ops_exit_task(p);
+		task_rq_unlock(rq, p, &rf);
+	}
+}
+
+static void reweight_task_scx(struct rq *rq, struct task_struct *p,
+			      const struct load_weight *lw)
+{
+	lockdep_assert_rq_held(task_rq(p));
+
+	p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight));
+	if (SCX_HAS_OP(set_weight))
+		SCX_CALL_OP_TASK(SCX_KF_REST, set_weight, p, p->scx.weight);
+}
+
+static void prio_changed_scx(struct rq *rq, struct task_struct *p, int oldprio)
+{
+}
+
+static void switching_to_scx(struct rq *rq, struct task_struct *p)
+{
+	scx_ops_enable_task(p);
+
+	/*
+	 * set_cpus_allowed_scx() is not called while @p is associated with a
+	 * different scheduler class. Keep the BPF scheduler up-to-date.
+	 */
+	if (SCX_HAS_OP(set_cpumask))
+		SCX_CALL_OP_TASK(SCX_KF_REST, set_cpumask, p,
+				 (struct cpumask *)p->cpus_ptr);
+}
+
+static void switched_from_scx(struct rq *rq, struct task_struct *p)
+{
+	scx_ops_disable_task(p);
+}
+
+static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p,int wake_flags) {}
+static void switched_to_scx(struct rq *rq, struct task_struct *p) {}
+
+int scx_check_setscheduler(struct task_struct *p, int policy)
+{
+	lockdep_assert_rq_held(task_rq(p));
+
+	/* if disallow, reject transitioning into SCX */
+	if (scx_enabled() && READ_ONCE(p->scx.disallow) &&
+	    p->policy != policy && policy == SCHED_EXT)
+		return -EACCES;
+
+	return 0;
+}
+
+#ifdef CONFIG_NO_HZ_FULL
+bool scx_can_stop_tick(struct rq *rq)
+{
+	struct task_struct *p = rq->curr;
+
+	if (scx_ops_bypassing())
+		return false;
+
+	if (p->sched_class != &ext_sched_class)
+		return true;
+
+	/*
+	 * @rq can dispatch from different DSQs, so we can't tell whether it
+	 * needs the tick or not by looking at nr_running. Allow stopping ticks
+	 * iff the BPF scheduler indicated so. See set_next_task_scx().
+	 */
+	return rq->scx.flags & SCX_RQ_CAN_STOP_TICK;
+}
+#endif
+
+/*
+ * Omitted operations:
+ *
+ * - wakeup_preempt: NOOP as it isn't useful in the wakeup path because the task
+ *   isn't tied to the CPU at that point. Preemption is implemented by resetting
+ *   the victim task's slice to 0 and triggering reschedule on the target CPU.
+ *
+ * - migrate_task_rq: Unnecessary as task to cpu mapping is transient.
+ *
+ * - task_fork/dead: We need fork/dead notifications for all tasks regardless of
+ *   their current sched_class. Call them directly from sched core instead.
+ */
+DEFINE_SCHED_CLASS(ext) = {
+	.enqueue_task		= enqueue_task_scx,
+	.dequeue_task		= dequeue_task_scx,
+	.yield_task		= yield_task_scx,
+	.yield_to_task		= yield_to_task_scx,
+
+	.wakeup_preempt		= wakeup_preempt_scx,
+
+	.pick_next_task		= pick_next_task_scx,
+
+	.put_prev_task		= put_prev_task_scx,
+	.set_next_task		= set_next_task_scx,
+
+	.switch_class		= switch_class_scx,
+
+#ifdef CONFIG_SMP
+	.balance		= balance_scx,
+	.select_task_rq		= select_task_rq_scx,
+	.task_woken		= task_woken_scx,
+	.set_cpus_allowed	= set_cpus_allowed_scx,
+
+	.rq_online		= rq_online_scx,
+	.rq_offline		= rq_offline_scx,
+#endif
+
+#ifdef CONFIG_SCHED_CORE
+	.pick_task		= pick_task_scx,
+#endif
+
+	.task_tick		= task_tick_scx,
+
+	.switching_to		= switching_to_scx,
+	.switched_from		= switched_from_scx,
+	.switched_to		= switched_to_scx,
+	.reweight_task		= reweight_task_scx,
+	.prio_changed		= prio_changed_scx,
+
+	.update_curr		= update_curr_scx,
+
+#ifdef CONFIG_UCLAMP_TASK
+	.uclamp_enabled		= 1,
+#endif
+};
+
+static void init_dsq(struct scx_dispatch_q *dsq, u64 dsq_id)
+{
+	memset(dsq, 0, sizeof(*dsq));
+
+	raw_spin_lock_init(&dsq->lock);
+	INIT_LIST_HEAD(&dsq->list);
+	dsq->id = dsq_id;
+}
+
+static struct scx_dispatch_q *create_dsq(u64 dsq_id, int node)
+{
+	struct scx_dispatch_q *dsq;
+	int ret;
+
+	if (dsq_id & SCX_DSQ_FLAG_BUILTIN)
+		return ERR_PTR(-EINVAL);
+
+	dsq = kmalloc_node(sizeof(*dsq), GFP_KERNEL, node);
+	if (!dsq)
+		return ERR_PTR(-ENOMEM);
+
+	init_dsq(dsq, dsq_id);
+
+	ret = rhashtable_insert_fast(&dsq_hash, &dsq->hash_node,
+				     dsq_hash_params);
+	if (ret) {
+		kfree(dsq);
+		return ERR_PTR(ret);
+	}
+	return dsq;
+}
+
+static void free_dsq_irq_workfn(struct irq_work *irq_work)
+{
+	struct llist_node *to_free = llist_del_all(&dsqs_to_free);
+	struct scx_dispatch_q *dsq, *tmp_dsq;
+
+	llist_for_each_entry_safe(dsq, tmp_dsq, to_free, free_node)
+		kfree_rcu(dsq, rcu);
+}
+
+static DEFINE_IRQ_WORK(free_dsq_irq_work, free_dsq_irq_workfn);
+
+static void destroy_dsq(u64 dsq_id)
+{
+	struct scx_dispatch_q *dsq;
+	unsigned long flags;
+
+	rcu_read_lock();
+
+	dsq = find_user_dsq(dsq_id);
+	if (!dsq)
+		goto out_unlock_rcu;
+
+	raw_spin_lock_irqsave(&dsq->lock, flags);
+
+	if (dsq->nr) {
+		scx_ops_error("attempting to destroy in-use dsq 0x%016llx (nr=%u)",
+			      dsq->id, dsq->nr);
+		goto out_unlock_dsq;
+	}
+
+	if (rhashtable_remove_fast(&dsq_hash, &dsq->hash_node, dsq_hash_params))
+		goto out_unlock_dsq;
+
+	/*
+	 * Mark dead by invalidating ->id to prevent dispatch_enqueue() from
+	 * queueing more tasks. As this function can be called from anywhere,
+	 * freeing is bounced through an irq work to avoid nesting RCU
+	 * operations inside scheduler locks.
+	 */
+	dsq->id = SCX_DSQ_INVALID;
+	llist_add(&dsq->free_node, &dsqs_to_free);
+	irq_work_queue(&free_dsq_irq_work);
+
+out_unlock_dsq:
+	raw_spin_unlock_irqrestore(&dsq->lock, flags);
+out_unlock_rcu:
+	rcu_read_unlock();
+}
+
+
+/********************************************************************************
+ * Sysfs interface and ops enable/disable.
+ */
+
+#define SCX_ATTR(_name)								\
+	static struct kobj_attribute scx_attr_##_name = {			\
+		.attr = { .name = __stringify(_name), .mode = 0444 },		\
+		.show = scx_attr_##_name##_show,				\
+	}
+
+static ssize_t scx_attr_state_show(struct kobject *kobj,
+				   struct kobj_attribute *ka, char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+			  scx_ops_enable_state_str[scx_ops_enable_state()]);
+}
+SCX_ATTR(state);
+
+static ssize_t scx_attr_switch_all_show(struct kobject *kobj,
+					struct kobj_attribute *ka, char *buf)
+{
+	return sysfs_emit(buf, "%d\n", READ_ONCE(scx_switching_all));
+}
+SCX_ATTR(switch_all);
+
+static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj,
+					 struct kobj_attribute *ka, char *buf)
+{
+	return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_nr_rejected));
+}
+SCX_ATTR(nr_rejected);
+
+static ssize_t scx_attr_hotplug_seq_show(struct kobject *kobj,
+					 struct kobj_attribute *ka, char *buf)
+{
+	return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_hotplug_seq));
+}
+SCX_ATTR(hotplug_seq);
+
+static struct attribute *scx_global_attrs[] = {
+	&scx_attr_state.attr,
+	&scx_attr_switch_all.attr,
+	&scx_attr_nr_rejected.attr,
+	&scx_attr_hotplug_seq.attr,
+	NULL,
+};
+
+static const struct attribute_group scx_global_attr_group = {
+	.attrs = scx_global_attrs,
+};
+
+static void scx_kobj_release(struct kobject *kobj)
+{
+	kfree(kobj);
+}
+
+static ssize_t scx_attr_ops_show(struct kobject *kobj,
+				 struct kobj_attribute *ka, char *buf)
+{
+	return sysfs_emit(buf, "%s\n", scx_ops.name);
+}
+SCX_ATTR(ops);
+
+static struct attribute *scx_sched_attrs[] = {
+	&scx_attr_ops.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(scx_sched);
+
+static const struct kobj_type scx_ktype = {
+	.release = scx_kobj_release,
+	.sysfs_ops = &kobj_sysfs_ops,
+	.default_groups = scx_sched_groups,
+};
+
+static int scx_uevent(const struct kobject *kobj, struct kobj_uevent_env *env)
+{
+	return add_uevent_var(env, "SCXOPS=%s", scx_ops.name);
+}
+
+static const struct kset_uevent_ops scx_uevent_ops = {
+	.uevent = scx_uevent,
+};
+
+/*
+ * Used by sched_fork() and __setscheduler_prio() to pick the matching
+ * sched_class. dl/rt are already handled.
+ */
+bool task_should_scx(struct task_struct *p)
+{
+	if (!scx_enabled() ||
+	    unlikely(scx_ops_enable_state() == SCX_OPS_DISABLING))
+		return false;
+	if (READ_ONCE(scx_switching_all))
+		return true;
+	return p->policy == SCHED_EXT;
+}
+
+/**
+ * scx_ops_bypass - [Un]bypass scx_ops and guarantee forward progress
+ *
+ * Bypassing guarantees that all runnable tasks make forward progress without
+ * trusting the BPF scheduler. We can't grab any mutexes or rwsems as they might
+ * be held by tasks that the BPF scheduler is forgetting to run, which
+ * unfortunately also excludes toggling the static branches.
+ *
+ * Let's work around by overriding a couple ops and modifying behaviors based on
+ * the DISABLING state and then cycling the queued tasks through dequeue/enqueue
+ * to force global FIFO scheduling.
+ *
+ * a. ops.enqueue() is ignored and tasks are queued in simple global FIFO order.
+ *
+ * b. ops.dispatch() is ignored.
+ *
+ * c. balance_scx() never sets %SCX_TASK_BAL_KEEP as the slice value can't be
+ *    trusted. Whenever a tick triggers, the running task is rotated to the tail
+ *    of the queue with core_sched_at touched.
+ *
+ * d. pick_next_task() suppresses zero slice warning.
+ *
+ * e. scx_bpf_kick_cpu() is disabled to avoid irq_work malfunction during PM
+ *    operations.
+ *
+ * f. scx_prio_less() reverts to the default core_sched_at order.
+ */
+static void scx_ops_bypass(bool bypass)
+{
+	int depth, cpu;
+
+	if (bypass) {
+		depth = atomic_inc_return(&scx_ops_bypass_depth);
+		WARN_ON_ONCE(depth <= 0);
+		if (depth != 1)
+			return;
+	} else {
+		depth = atomic_dec_return(&scx_ops_bypass_depth);
+		WARN_ON_ONCE(depth < 0);
+		if (depth != 0)
+			return;
+	}
+
+	/*
+	 * We need to guarantee that no tasks are on the BPF scheduler while
+	 * bypassing. Either we see enabled or the enable path sees the
+	 * increased bypass_depth before moving tasks to SCX.
+	 */
+	if (!scx_enabled())
+		return;
+
+	/*
+	 * No task property is changing. We just need to make sure all currently
+	 * queued tasks are re-queued according to the new scx_ops_bypassing()
+	 * state. As an optimization, walk each rq's runnable_list instead of
+	 * the scx_tasks list.
+	 *
+	 * This function can't trust the scheduler and thus can't use
+	 * cpus_read_lock(). Walk all possible CPUs instead of online.
+	 */
+	for_each_possible_cpu(cpu) {
+		struct rq *rq = cpu_rq(cpu);
+		struct rq_flags rf;
+		struct task_struct *p, *n;
+
+		rq_lock_irqsave(rq, &rf);
+
+		/*
+		 * The use of list_for_each_entry_safe_reverse() is required
+		 * because each task is going to be removed from and added back
+		 * to the runnable_list during iteration. Because they're added
+		 * to the tail of the list, safe reverse iteration can still
+		 * visit all nodes.
+		 */
+		list_for_each_entry_safe_reverse(p, n, &rq->scx.runnable_list,
+						 scx.runnable_node) {
+			struct sched_enq_and_set_ctx ctx;
+
+			/* cycling deq/enq is enough, see the function comment */
+			sched_deq_and_put_task(p, DEQUEUE_SAVE | DEQUEUE_MOVE, &ctx);
+			sched_enq_and_set_task(&ctx);
+		}
+
+		rq_unlock_irqrestore(rq, &rf);
+
+		/* kick to restore ticks */
+		resched_cpu(cpu);
+	}
+}
+
+static void free_exit_info(struct scx_exit_info *ei)
+{
+	kfree(ei->dump);
+	kfree(ei->msg);
+	kfree(ei->bt);
+	kfree(ei);
+}
+
+static struct scx_exit_info *alloc_exit_info(size_t exit_dump_len)
+{
+	struct scx_exit_info *ei;
+
+	ei = kzalloc(sizeof(*ei), GFP_KERNEL);
+	if (!ei)
+		return NULL;
+
+	ei->bt = kcalloc(SCX_EXIT_BT_LEN, sizeof(ei->bt[0]), GFP_KERNEL);
+	ei->msg = kzalloc(SCX_EXIT_MSG_LEN, GFP_KERNEL);
+	ei->dump = kzalloc(exit_dump_len, GFP_KERNEL);
+
+	if (!ei->bt || !ei->msg || !ei->dump) {
+		free_exit_info(ei);
+		return NULL;
+	}
+
+	return ei;
+}
+
+static const char *scx_exit_reason(enum scx_exit_kind kind)
+{
+	switch (kind) {
+	case SCX_EXIT_UNREG:
+		return "Scheduler unregistered from user space";
+	case SCX_EXIT_UNREG_BPF:
+		return "Scheduler unregistered from BPF";
+	case SCX_EXIT_UNREG_KERN:
+		return "Scheduler unregistered from the main kernel";
+	case SCX_EXIT_SYSRQ:
+		return "disabled by sysrq-S";
+	case SCX_EXIT_ERROR:
+		return "runtime error";
+	case SCX_EXIT_ERROR_BPF:
+		return "scx_bpf_error";
+	case SCX_EXIT_ERROR_STALL:
+		return "runnable task stall";
+	default:
+		return "<UNKNOWN>";
+	}
+}
+
+static void scx_ops_disable_workfn(struct kthread_work *work)
+{
+	struct scx_exit_info *ei = scx_exit_info;
+	struct scx_task_iter sti;
+	struct task_struct *p;
+	struct rhashtable_iter rht_iter;
+	struct scx_dispatch_q *dsq;
+	int i, kind;
+
+	kind = atomic_read(&scx_exit_kind);
+	while (true) {
+		/*
+		 * NONE indicates that a new scx_ops has been registered since
+		 * disable was scheduled - don't kill the new ops. DONE
+		 * indicates that the ops has already been disabled.
+		 */
+		if (kind == SCX_EXIT_NONE || kind == SCX_EXIT_DONE)
+			return;
+		if (atomic_try_cmpxchg(&scx_exit_kind, &kind, SCX_EXIT_DONE))
+			break;
+	}
+	ei->kind = kind;
+	ei->reason = scx_exit_reason(ei->kind);
+
+	/* guarantee forward progress by bypassing scx_ops */
+	scx_ops_bypass(true);
+
+	switch (scx_ops_set_enable_state(SCX_OPS_DISABLING)) {
+	case SCX_OPS_DISABLING:
+		WARN_ONCE(true, "sched_ext: duplicate disabling instance?");
+		break;
+	case SCX_OPS_DISABLED:
+		pr_warn("sched_ext: ops error detected without ops (%s)\n",
+			scx_exit_info->msg);
+		WARN_ON_ONCE(scx_ops_set_enable_state(SCX_OPS_DISABLED) !=
+			     SCX_OPS_DISABLING);
+		goto done;
+	default:
+		break;
+	}
+
+	/*
+	 * Here, every runnable task is guaranteed to make forward progress and
+	 * we can safely use blocking synchronization constructs. Actually
+	 * disable ops.
+	 */
+	mutex_lock(&scx_ops_enable_mutex);
+
+	static_branch_disable(&__scx_switched_all);
+	WRITE_ONCE(scx_switching_all, false);
+
+	/*
+	 * Avoid racing against fork. See scx_ops_enable() for explanation on
+	 * the locking order.
+	 */
+	percpu_down_write(&scx_fork_rwsem);
+	cpus_read_lock();
+
+	spin_lock_irq(&scx_tasks_lock);
+	scx_task_iter_init(&sti);
+	/*
+	 * Invoke scx_ops_exit_task() on all non-idle tasks, including
+	 * TASK_DEAD tasks. Because dead tasks may have a nonzero refcount,
+	 * we may not have invoked sched_ext_free() on them by the time a
+	 * scheduler is disabled. We must therefore exit the task here, or we'd
+	 * fail to invoke ops.exit_task(), as the scheduler will have been
+	 * unloaded by the time the task is subsequently exited on the
+	 * sched_ext_free() path.
+	 */
+	while ((p = scx_task_iter_next_locked(&sti, true))) {
+		const struct sched_class *old_class = p->sched_class;
+		struct sched_enq_and_set_ctx ctx;
+
+		if (READ_ONCE(p->__state) != TASK_DEAD) {
+			sched_deq_and_put_task(p, DEQUEUE_SAVE | DEQUEUE_MOVE,
+					       &ctx);
+
+			p->scx.slice = min_t(u64, p->scx.slice, SCX_SLICE_DFL);
+			__setscheduler_prio(p, p->prio);
+			check_class_changing(task_rq(p), p, old_class);
+
+			sched_enq_and_set_task(&ctx);
+
+			check_class_changed(task_rq(p), p, old_class, p->prio);
+		}
+		scx_ops_exit_task(p);
+	}
+	scx_task_iter_exit(&sti);
+	spin_unlock_irq(&scx_tasks_lock);
+
+	/* no task is on scx, turn off all the switches and flush in-progress calls */
+	static_branch_disable_cpuslocked(&__scx_ops_enabled);
+	for (i = SCX_OPI_BEGIN; i < SCX_OPI_END; i++)
+		static_branch_disable_cpuslocked(&scx_has_op[i]);
+	static_branch_disable_cpuslocked(&scx_ops_enq_last);
+	static_branch_disable_cpuslocked(&scx_ops_enq_exiting);
+	static_branch_disable_cpuslocked(&scx_ops_cpu_preempt);
+	static_branch_disable_cpuslocked(&scx_builtin_idle_enabled);
+	synchronize_rcu();
+
+	cpus_read_unlock();
+	percpu_up_write(&scx_fork_rwsem);
+
+	if (ei->kind >= SCX_EXIT_ERROR) {
+		printk(KERN_ERR "sched_ext: BPF scheduler \"%s\" errored, disabling\n", scx_ops.name);
+
+		if (ei->msg[0] == '\0')
+			printk(KERN_ERR "sched_ext: %s\n", ei->reason);
+		else
+			printk(KERN_ERR "sched_ext: %s (%s)\n", ei->reason, ei->msg);
+
+		stack_trace_print(ei->bt, ei->bt_len, 2);
+	}
+
+	if (scx_ops.exit)
+		SCX_CALL_OP(SCX_KF_UNLOCKED, exit, ei);
+
+	cancel_delayed_work_sync(&scx_watchdog_work);
+
+	/*
+	 * Delete the kobject from the hierarchy eagerly in addition to just
+	 * dropping a reference. Otherwise, if the object is deleted
+	 * asynchronously, sysfs could observe an object of the same name still
+	 * in the hierarchy when another scheduler is loaded.
+	 */
+	kobject_del(scx_root_kobj);
+	kobject_put(scx_root_kobj);
+	scx_root_kobj = NULL;
+
+	memset(&scx_ops, 0, sizeof(scx_ops));
+
+	rhashtable_walk_enter(&dsq_hash, &rht_iter);
+	do {
+		rhashtable_walk_start(&rht_iter);
+
+		while ((dsq = rhashtable_walk_next(&rht_iter)) && !IS_ERR(dsq))
+			destroy_dsq(dsq->id);
+
+		rhashtable_walk_stop(&rht_iter);
+	} while (dsq == ERR_PTR(-EAGAIN));
+	rhashtable_walk_exit(&rht_iter);
+
+	free_percpu(scx_dsp_ctx);
+	scx_dsp_ctx = NULL;
+	scx_dsp_max_batch = 0;
+
+	free_exit_info(scx_exit_info);
+	scx_exit_info = NULL;
+
+	mutex_unlock(&scx_ops_enable_mutex);
+
+	WARN_ON_ONCE(scx_ops_set_enable_state(SCX_OPS_DISABLED) !=
+		     SCX_OPS_DISABLING);
+done:
+	scx_ops_bypass(false);
+}
+
+static DEFINE_KTHREAD_WORK(scx_ops_disable_work, scx_ops_disable_workfn);
+
+static void schedule_scx_ops_disable_work(void)
+{
+	struct kthread_worker *helper = READ_ONCE(scx_ops_helper);
+
+	/*
+	 * We may be called spuriously before the first bpf_sched_ext_reg(). If
+	 * scx_ops_helper isn't set up yet, there's nothing to do.
+	 */
+	if (helper)
+		kthread_queue_work(helper, &scx_ops_disable_work);
+}
+
+static void scx_ops_disable(enum scx_exit_kind kind)
+{
+	int none = SCX_EXIT_NONE;
+
+	if (WARN_ON_ONCE(kind == SCX_EXIT_NONE || kind == SCX_EXIT_DONE))
+		kind = SCX_EXIT_ERROR;
+
+	atomic_try_cmpxchg(&scx_exit_kind, &none, kind);
+
+	schedule_scx_ops_disable_work();
+}
+
+static void dump_newline(struct seq_buf *s)
+{
+	trace_sched_ext_dump("");
+
+	/* @s may be zero sized and seq_buf triggers WARN if so */
+	if (s->size)
+		seq_buf_putc(s, '\n');
+}
+
+static __printf(2, 3) void dump_line(struct seq_buf *s, const char *fmt, ...)
+{
+	va_list args;
+
+#ifdef CONFIG_TRACEPOINTS
+	if (trace_sched_ext_dump_enabled()) {
+		/* protected by scx_dump_state()::dump_lock */
+		static char line_buf[SCX_EXIT_MSG_LEN];
+
+		va_start(args, fmt);
+		vscnprintf(line_buf, sizeof(line_buf), fmt, args);
+		va_end(args);
+
+		trace_sched_ext_dump(line_buf);
+	}
+#endif
+	/* @s may be zero sized and seq_buf triggers WARN if so */
+	if (s->size) {
+		va_start(args, fmt);
+		seq_buf_vprintf(s, fmt, args);
+		va_end(args);
+
+		seq_buf_putc(s, '\n');
+	}
+}
+
+static void dump_stack_trace(struct seq_buf *s, const char *prefix,
+			     const unsigned long *bt, unsigned int len)
+{
+	unsigned int i;
+
+	for (i = 0; i < len; i++)
+		dump_line(s, "%s%pS", prefix, (void *)bt[i]);
+}
+
+static void ops_dump_init(struct seq_buf *s, const char *prefix)
+{
+	struct scx_dump_data *dd = &scx_dump_data;
+
+	lockdep_assert_irqs_disabled();
+
+	dd->cpu = smp_processor_id();		/* allow scx_bpf_dump() */
+	dd->first = true;
+	dd->cursor = 0;
+	dd->s = s;
+	dd->prefix = prefix;
+}
+
+static void ops_dump_flush(void)
+{
+	struct scx_dump_data *dd = &scx_dump_data;
+	char *line = dd->buf.line;
+
+	if (!dd->cursor)
+		return;
+
+	/*
+	 * There's something to flush and this is the first line. Insert a blank
+	 * line to distinguish ops dump.
+	 */
+	if (dd->first) {
+		dump_newline(dd->s);
+		dd->first = false;
+	}
+
+	/*
+	 * There may be multiple lines in $line. Scan and emit each line
+	 * separately.
+	 */
+	while (true) {
+		char *end = line;
+		char c;
+
+		while (*end != '\n' && *end != '\0')
+			end++;
+
+		/*
+		 * If $line overflowed, it may not have newline at the end.
+		 * Always emit with a newline.
+		 */
+		c = *end;
+		*end = '\0';
+		dump_line(dd->s, "%s%s", dd->prefix, line);
+		if (c == '\0')
+			break;
+
+		/* move to the next line */
+		end++;
+		if (*end == '\0')
+			break;
+		line = end;
+	}
+
+	dd->cursor = 0;
+}
+
+static void ops_dump_exit(void)
+{
+	ops_dump_flush();
+	scx_dump_data.cpu = -1;
+}
+
+static void scx_dump_task(struct seq_buf *s, struct scx_dump_ctx *dctx,
+			  struct task_struct *p, char marker)
+{
+	static unsigned long bt[SCX_EXIT_BT_LEN];
+	char dsq_id_buf[19] = "(n/a)";
+	unsigned long ops_state = atomic_long_read(&p->scx.ops_state);
+	unsigned int bt_len;
+
+	if (p->scx.dsq)
+		scnprintf(dsq_id_buf, sizeof(dsq_id_buf), "0x%llx",
+			  (unsigned long long)p->scx.dsq->id);
+
+	dump_newline(s);
+	dump_line(s, " %c%c %s[%d] %+ldms",
+		  marker, task_state_to_char(p), p->comm, p->pid,
+		  jiffies_delta_msecs(p->scx.runnable_at, dctx->at_jiffies));
+	dump_line(s, "      scx_state/flags=%u/0x%x dsq_flags=0x%x ops_state/qseq=%lu/%lu",
+		  scx_get_task_state(p), p->scx.flags & ~SCX_TASK_STATE_MASK,
+		  p->scx.dsq_flags, ops_state & SCX_OPSS_STATE_MASK,
+		  ops_state >> SCX_OPSS_QSEQ_SHIFT);
+	dump_line(s, "      sticky/holding_cpu=%d/%d dsq_id=%s dsq_vtime=%llu",
+		  p->scx.sticky_cpu, p->scx.holding_cpu, dsq_id_buf,
+		  p->scx.dsq_vtime);
+	dump_line(s, "      cpus=%*pb", cpumask_pr_args(p->cpus_ptr));
+
+	if (SCX_HAS_OP(dump_task)) {
+		ops_dump_init(s, "    ");
+		SCX_CALL_OP(SCX_KF_REST, dump_task, dctx, p);
+		ops_dump_exit();
+	}
+
+	bt_len = stack_trace_save_tsk(p, bt, SCX_EXIT_BT_LEN, 1);
+	if (bt_len) {
+		dump_newline(s);
+		dump_stack_trace(s, "    ", bt, bt_len);
+	}
+}
+
+static void scx_dump_state(struct scx_exit_info *ei, size_t dump_len)
+{
+	static DEFINE_SPINLOCK(dump_lock);
+	static const char trunc_marker[] = "\n\n~~~~ TRUNCATED ~~~~\n";
+	struct scx_dump_ctx dctx = {
+		.kind = ei->kind,
+		.exit_code = ei->exit_code,
+		.reason = ei->reason,
+		.at_ns = ktime_get_ns(),
+		.at_jiffies = jiffies,
+	};
+	struct seq_buf s;
+	unsigned long flags;
+	char *buf;
+	int cpu;
+
+	spin_lock_irqsave(&dump_lock, flags);
+
+	seq_buf_init(&s, ei->dump, dump_len);
+
+	if (ei->kind == SCX_EXIT_NONE) {
+		dump_line(&s, "Debug dump triggered by %s", ei->reason);
+	} else {
+		dump_line(&s, "%s[%d] triggered exit kind %d:",
+			  current->comm, current->pid, ei->kind);
+		dump_line(&s, "  %s (%s)", ei->reason, ei->msg);
+		dump_newline(&s);
+		dump_line(&s, "Backtrace:");
+		dump_stack_trace(&s, "  ", ei->bt, ei->bt_len);
+	}
+
+	if (SCX_HAS_OP(dump)) {
+		ops_dump_init(&s, "");
+		SCX_CALL_OP(SCX_KF_UNLOCKED, dump, &dctx);
+		ops_dump_exit();
+	}
+
+	dump_newline(&s);
+	dump_line(&s, "CPU states");
+	dump_line(&s, "----------");
+
+	for_each_possible_cpu(cpu) {
+		struct rq *rq = cpu_rq(cpu);
+		struct rq_flags rf;
+		struct task_struct *p;
+		struct seq_buf ns;
+		size_t avail, used;
+		bool idle;
+
+		rq_lock(rq, &rf);
+
+		idle = list_empty(&rq->scx.runnable_list) &&
+			rq->curr->sched_class == &idle_sched_class;
+
+		if (idle && !SCX_HAS_OP(dump_cpu))
+			goto next;
+
+		/*
+		 * We don't yet know whether ops.dump_cpu() will produce output
+		 * and we may want to skip the default CPU dump if it doesn't.
+		 * Use a nested seq_buf to generate the standard dump so that we
+		 * can decide whether to commit later.
+		 */
+		avail = seq_buf_get_buf(&s, &buf);
+		seq_buf_init(&ns, buf, avail);
+
+		dump_newline(&ns);
+		dump_line(&ns, "CPU %-4d: nr_run=%u flags=0x%x cpu_rel=%d ops_qseq=%lu pnt_seq=%lu",
+			  cpu, rq->scx.nr_running, rq->scx.flags,
+			  rq->scx.cpu_released, rq->scx.ops_qseq,
+			  rq->scx.pnt_seq);
+		dump_line(&ns, "          curr=%s[%d] class=%ps",
+			  rq->curr->comm, rq->curr->pid,
+			  rq->curr->sched_class);
+		if (!cpumask_empty(rq->scx.cpus_to_kick))
+			dump_line(&ns, "  cpus_to_kick   : %*pb",
+				  cpumask_pr_args(rq->scx.cpus_to_kick));
+		if (!cpumask_empty(rq->scx.cpus_to_kick_if_idle))
+			dump_line(&ns, "  idle_to_kick   : %*pb",
+				  cpumask_pr_args(rq->scx.cpus_to_kick_if_idle));
+		if (!cpumask_empty(rq->scx.cpus_to_preempt))
+			dump_line(&ns, "  cpus_to_preempt: %*pb",
+				  cpumask_pr_args(rq->scx.cpus_to_preempt));
+		if (!cpumask_empty(rq->scx.cpus_to_wait))
+			dump_line(&ns, "  cpus_to_wait   : %*pb",
+				  cpumask_pr_args(rq->scx.cpus_to_wait));
+
+		used = seq_buf_used(&ns);
+		if (SCX_HAS_OP(dump_cpu)) {
+			ops_dump_init(&ns, "  ");
+			SCX_CALL_OP(SCX_KF_REST, dump_cpu, &dctx, cpu, idle);
+			ops_dump_exit();
+		}
+
+		/*
+		 * If idle && nothing generated by ops.dump_cpu(), there's
+		 * nothing interesting. Skip.
+		 */
+		if (idle && used == seq_buf_used(&ns))
+			goto next;
+
+		/*
+		 * $s may already have overflowed when $ns was created. If so,
+		 * calling commit on it will trigger BUG.
+		 */
+		if (avail) {
+			seq_buf_commit(&s, seq_buf_used(&ns));
+			if (seq_buf_has_overflowed(&ns))
+				seq_buf_set_overflow(&s);
+		}
+
+		if (rq->curr->sched_class == &ext_sched_class)
+			scx_dump_task(&s, &dctx, rq->curr, '*');
+
+		list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node)
+			scx_dump_task(&s, &dctx, p, ' ');
+	next:
+		rq_unlock(rq, &rf);
+	}
+
+	if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker))
+		memcpy(ei->dump + dump_len - sizeof(trunc_marker),
+		       trunc_marker, sizeof(trunc_marker));
+
+	spin_unlock_irqrestore(&dump_lock, flags);
+}
+
+static void scx_ops_error_irq_workfn(struct irq_work *irq_work)
+{
+	struct scx_exit_info *ei = scx_exit_info;
+
+	if (ei->kind >= SCX_EXIT_ERROR)
+		scx_dump_state(ei, scx_ops.exit_dump_len);
+
+	schedule_scx_ops_disable_work();
+}
+
+static DEFINE_IRQ_WORK(scx_ops_error_irq_work, scx_ops_error_irq_workfn);
+
+static __printf(3, 4) void scx_ops_exit_kind(enum scx_exit_kind kind,
+					     s64 exit_code,
+					     const char *fmt, ...)
+{
+	struct scx_exit_info *ei = scx_exit_info;
+	int none = SCX_EXIT_NONE;
+	va_list args;
+
+	if (!atomic_try_cmpxchg(&scx_exit_kind, &none, kind))
+		return;
+
+	ei->exit_code = exit_code;
+
+	if (kind >= SCX_EXIT_ERROR)
+		ei->bt_len = stack_trace_save(ei->bt, SCX_EXIT_BT_LEN, 1);
+
+	va_start(args, fmt);
+	vscnprintf(ei->msg, SCX_EXIT_MSG_LEN, fmt, args);
+	va_end(args);
+
+	/*
+	 * Set ei->kind and ->reason for scx_dump_state(). They'll be set again
+	 * in scx_ops_disable_workfn().
+	 */
+	ei->kind = kind;
+	ei->reason = scx_exit_reason(ei->kind);
+
+	irq_work_queue(&scx_ops_error_irq_work);
+}
+
+static struct kthread_worker *scx_create_rt_helper(const char *name)
+{
+	struct kthread_worker *helper;
+
+	helper = kthread_create_worker(0, name);
+	if (helper)
+		sched_set_fifo(helper->task);
+	return helper;
+}
+
+static void check_hotplug_seq(const struct sched_ext_ops *ops)
+{
+	unsigned long long global_hotplug_seq;
+
+	/*
+	 * If a hotplug event has occurred between when a scheduler was
+	 * initialized, and when we were able to attach, exit and notify user
+	 * space about it.
+	 */
+	if (ops->hotplug_seq) {
+		global_hotplug_seq = atomic_long_read(&scx_hotplug_seq);
+		if (ops->hotplug_seq != global_hotplug_seq) {
+			scx_ops_exit(SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG,
+				     "expected hotplug seq %llu did not match actual %llu",
+				     ops->hotplug_seq, global_hotplug_seq);
+		}
+	}
+}
+
+static int validate_ops(const struct sched_ext_ops *ops)
+{
+	/*
+	 * It doesn't make sense to specify the SCX_OPS_ENQ_LAST flag if the
+	 * ops.enqueue() callback isn't implemented.
+	 */
+	if ((ops->flags & SCX_OPS_ENQ_LAST) && !ops->enqueue) {
+		scx_ops_error("SCX_OPS_ENQ_LAST requires ops.enqueue() to be implemented");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int scx_ops_enable(struct sched_ext_ops *ops)
+{
+	struct scx_task_iter sti;
+	struct task_struct *p;
+	unsigned long timeout;
+	int i, cpu, ret;
+
+	if (!cpumask_equal(housekeeping_cpumask(HK_TYPE_DOMAIN),
+			   cpu_possible_mask)) {
+		pr_err("sched_ext: Not compatible with \"isolcpus=\" domain isolation");
+		return -EINVAL;
+	}
+
+	mutex_lock(&scx_ops_enable_mutex);
+
+	if (!scx_ops_helper) {
+		WRITE_ONCE(scx_ops_helper,
+			   scx_create_rt_helper("sched_ext_ops_helper"));
+		if (!scx_ops_helper) {
+			ret = -ENOMEM;
+			goto err_unlock;
+		}
+	}
+
+	if (scx_ops_enable_state() != SCX_OPS_DISABLED) {
+		ret = -EBUSY;
+		goto err_unlock;
+	}
+
+	scx_root_kobj = kzalloc(sizeof(*scx_root_kobj), GFP_KERNEL);
+	if (!scx_root_kobj) {
+		ret = -ENOMEM;
+		goto err_unlock;
+	}
+
+	scx_root_kobj->kset = scx_kset;
+	ret = kobject_init_and_add(scx_root_kobj, &scx_ktype, NULL, "root");
+	if (ret < 0)
+		goto err;
+
+	scx_exit_info = alloc_exit_info(ops->exit_dump_len);
+	if (!scx_exit_info) {
+		ret = -ENOMEM;
+		goto err_del;
+	}
+
+	/*
+	 * Set scx_ops, transition to PREPPING and clear exit info to arm the
+	 * disable path. Failure triggers full disabling from here on.
+	 */
+	scx_ops = *ops;
+
+	WARN_ON_ONCE(scx_ops_set_enable_state(SCX_OPS_PREPPING) !=
+		     SCX_OPS_DISABLED);
+
+	atomic_set(&scx_exit_kind, SCX_EXIT_NONE);
+	scx_warned_zero_slice = false;
+
+	atomic_long_set(&scx_nr_rejected, 0);
+
+	for_each_possible_cpu(cpu)
+		cpu_rq(cpu)->scx.cpuperf_target = SCX_CPUPERF_ONE;
+
+	/*
+	 * Keep CPUs stable during enable so that the BPF scheduler can track
+	 * online CPUs by watching ->on/offline_cpu() after ->init().
+	 */
+	cpus_read_lock();
+
+	if (scx_ops.init) {
+		ret = SCX_CALL_OP_RET(SCX_KF_SLEEPABLE, init);
+		if (ret) {
+			ret = ops_sanitize_err("init", ret);
+			goto err_disable_unlock_cpus;
+		}
+	}
+
+	for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++)
+		if (((void (**)(void))ops)[i])
+			static_branch_enable_cpuslocked(&scx_has_op[i]);
+
+	cpus_read_unlock();
+
+	ret = validate_ops(ops);
+	if (ret)
+		goto err_disable;
+
+	WARN_ON_ONCE(scx_dsp_ctx);
+	scx_dsp_max_batch = ops->dispatch_max_batch ?: SCX_DSP_DFL_MAX_BATCH;
+	scx_dsp_ctx = __alloc_percpu(struct_size_t(struct scx_dsp_ctx, buf,
+						   scx_dsp_max_batch),
+				     __alignof__(struct scx_dsp_ctx));
+	if (!scx_dsp_ctx) {
+		ret = -ENOMEM;
+		goto err_disable;
+	}
+
+	if (ops->timeout_ms)
+		timeout = msecs_to_jiffies(ops->timeout_ms);
+	else
+		timeout = SCX_WATCHDOG_MAX_TIMEOUT;
+
+	WRITE_ONCE(scx_watchdog_timeout, timeout);
+	WRITE_ONCE(scx_watchdog_timestamp, jiffies);
+	queue_delayed_work(system_unbound_wq, &scx_watchdog_work,
+			   scx_watchdog_timeout / 2);
+
+	/*
+	 * Lock out forks before opening the floodgate so that they don't wander
+	 * into the operations prematurely.
+	 *
+	 * We don't need to keep the CPUs stable but grab cpus_read_lock() to
+	 * ease future locking changes for cgroup suport.
+	 *
+	 * Note that cpu_hotplug_lock must nest inside scx_fork_rwsem due to the
+	 * following dependency chain:
+	 *
+	 *   scx_fork_rwsem --> pernet_ops_rwsem --> cpu_hotplug_lock
+	 */
+	percpu_down_write(&scx_fork_rwsem);
+	cpus_read_lock();
+
+	check_hotplug_seq(ops);
+
+	for (i = SCX_OPI_NORMAL_BEGIN; i < SCX_OPI_NORMAL_END; i++)
+		if (((void (**)(void))ops)[i])
+			static_branch_enable_cpuslocked(&scx_has_op[i]);
+
+	if (ops->flags & SCX_OPS_ENQ_LAST)
+		static_branch_enable_cpuslocked(&scx_ops_enq_last);
+
+	if (ops->flags & SCX_OPS_ENQ_EXITING)
+		static_branch_enable_cpuslocked(&scx_ops_enq_exiting);
+	if (scx_ops.cpu_acquire || scx_ops.cpu_release)
+		static_branch_enable_cpuslocked(&scx_ops_cpu_preempt);
+
+	if (!ops->update_idle || (ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE)) {
+		reset_idle_masks();
+		static_branch_enable_cpuslocked(&scx_builtin_idle_enabled);
+	} else {
+		static_branch_disable_cpuslocked(&scx_builtin_idle_enabled);
+	}
+
+	static_branch_enable_cpuslocked(&__scx_ops_enabled);
+
+	/*
+	 * Enable ops for every task. Fork is excluded by scx_fork_rwsem
+	 * preventing new tasks from being added. No need to exclude tasks
+	 * leaving as sched_ext_free() can handle both prepped and enabled
+	 * tasks. Prep all tasks first and then enable them with preemption
+	 * disabled.
+	 */
+	spin_lock_irq(&scx_tasks_lock);
+
+	scx_task_iter_init(&sti);
+	while ((p = scx_task_iter_next_locked(&sti, false))) {
+		get_task_struct(p);
+		scx_task_iter_rq_unlock(&sti);
+		spin_unlock_irq(&scx_tasks_lock);
+
+		ret = scx_ops_init_task(p, task_group(p), false);
+		if (ret) {
+			put_task_struct(p);
+			spin_lock_irq(&scx_tasks_lock);
+			scx_task_iter_exit(&sti);
+			spin_unlock_irq(&scx_tasks_lock);
+			pr_err("sched_ext: ops.init_task() failed (%d) for %s[%d] while loading\n",
+			       ret, p->comm, p->pid);
+			goto err_disable_unlock_all;
+		}
+
+		put_task_struct(p);
+		spin_lock_irq(&scx_tasks_lock);
+	}
+	scx_task_iter_exit(&sti);
+
+	/*
+	 * All tasks are prepped but are still ops-disabled. Ensure that
+	 * %current can't be scheduled out and switch everyone.
+	 * preempt_disable() is necessary because we can't guarantee that
+	 * %current won't be starved if scheduled out while switching.
+	 */
+	preempt_disable();
+
+	/*
+	 * From here on, the disable path must assume that tasks have ops
+	 * enabled and need to be recovered.
+	 *
+	 * Transition to ENABLING fails iff the BPF scheduler has already
+	 * triggered scx_bpf_error(). Returning an error code here would lose
+	 * the recorded error information. Exit indicating success so that the
+	 * error is notified through ops.exit() with all the details.
+	 */
+	if (!scx_ops_tryset_enable_state(SCX_OPS_ENABLING, SCX_OPS_PREPPING)) {
+		preempt_enable();
+		spin_unlock_irq(&scx_tasks_lock);
+		WARN_ON_ONCE(atomic_read(&scx_exit_kind) == SCX_EXIT_NONE);
+		ret = 0;
+		goto err_disable_unlock_all;
+	}
+
+	/*
+	 * We're fully committed and can't fail. The PREPPED -> ENABLED
+	 * transitions here are synchronized against sched_ext_free() through
+	 * scx_tasks_lock.
+	 */
+	WRITE_ONCE(scx_switching_all, !(ops->flags & SCX_OPS_SWITCH_PARTIAL));
+
+	scx_task_iter_init(&sti);
+	while ((p = scx_task_iter_next_locked(&sti, false))) {
+		const struct sched_class *old_class = p->sched_class;
+		struct sched_enq_and_set_ctx ctx;
+
+		sched_deq_and_put_task(p, DEQUEUE_SAVE | DEQUEUE_MOVE, &ctx);
+
+		scx_set_task_state(p, SCX_TASK_READY);
+		__setscheduler_prio(p, p->prio);
+		check_class_changing(task_rq(p), p, old_class);
+
+		sched_enq_and_set_task(&ctx);
+
+		check_class_changed(task_rq(p), p, old_class, p->prio);
+	}
+	scx_task_iter_exit(&sti);
+
+	spin_unlock_irq(&scx_tasks_lock);
+	preempt_enable();
+	cpus_read_unlock();
+	percpu_up_write(&scx_fork_rwsem);
+
+	/* see above ENABLING transition for the explanation on exiting with 0 */
+	if (!scx_ops_tryset_enable_state(SCX_OPS_ENABLED, SCX_OPS_ENABLING)) {
+		WARN_ON_ONCE(atomic_read(&scx_exit_kind) == SCX_EXIT_NONE);
+		ret = 0;
+		goto err_disable;
+	}
+
+	if (!(ops->flags & SCX_OPS_SWITCH_PARTIAL))
+		static_branch_enable(&__scx_switched_all);
+
+	kobject_uevent(scx_root_kobj, KOBJ_ADD);
+	mutex_unlock(&scx_ops_enable_mutex);
+
+	return 0;
+
+err_del:
+	kobject_del(scx_root_kobj);
+err:
+	kobject_put(scx_root_kobj);
+	scx_root_kobj = NULL;
+	if (scx_exit_info) {
+		free_exit_info(scx_exit_info);
+		scx_exit_info = NULL;
+	}
+err_unlock:
+	mutex_unlock(&scx_ops_enable_mutex);
+	return ret;
+
+err_disable_unlock_all:
+	percpu_up_write(&scx_fork_rwsem);
+err_disable_unlock_cpus:
+	cpus_read_unlock();
+err_disable:
+	mutex_unlock(&scx_ops_enable_mutex);
+	/* must be fully disabled before returning */
+	scx_ops_disable(SCX_EXIT_ERROR);
+	kthread_flush_work(&scx_ops_disable_work);
+	return ret;
+}
+
+
+/********************************************************************************
+ * bpf_struct_ops plumbing.
+ */
+#include <linux/bpf_verifier.h>
+#include <linux/bpf.h>
+#include <linux/btf.h>
+
+extern struct btf *btf_vmlinux;
+static const struct btf_type *task_struct_type;
+static u32 task_struct_type_id;
+
+static bool set_arg_maybe_null(const char *op, int arg_n, int off, int size,
+			       enum bpf_access_type type,
+			       const struct bpf_prog *prog,
+			       struct bpf_insn_access_aux *info)
+{
+	struct btf *btf = bpf_get_btf_vmlinux();
+	const struct bpf_struct_ops_desc *st_ops_desc;
+	const struct btf_member *member;
+	const struct btf_type *t;
+	u32 btf_id, member_idx;
+	const char *mname;
+
+	/* struct_ops op args are all sequential, 64-bit numbers */
+	if (off != arg_n * sizeof(__u64))
+		return false;
+
+	/* btf_id should be the type id of struct sched_ext_ops */
+	btf_id = prog->aux->attach_btf_id;
+	st_ops_desc = bpf_struct_ops_find(btf, btf_id);
+	if (!st_ops_desc)
+		return false;
+
+	/* BTF type of struct sched_ext_ops */
+	t = st_ops_desc->type;
+
+	member_idx = prog->expected_attach_type;
+	if (member_idx >= btf_type_vlen(t))
+		return false;
+
+	/*
+	 * Get the member name of this struct_ops program, which corresponds to
+	 * a field in struct sched_ext_ops. For example, the member name of the
+	 * dispatch struct_ops program (callback) is "dispatch".
+	 */
+	member = &btf_type_member(t)[member_idx];
+	mname = btf_name_by_offset(btf_vmlinux, member->name_off);
+
+	if (!strcmp(mname, op)) {
+		/*
+		 * The value is a pointer to a type (struct task_struct) given
+		 * by a BTF ID (PTR_TO_BTF_ID). It is trusted (PTR_TRUSTED),
+		 * however, can be a NULL (PTR_MAYBE_NULL). The BPF program
+		 * should check the pointer to make sure it is not NULL before
+		 * using it, or the verifier will reject the program.
+		 *
+		 * Longer term, this is something that should be addressed by
+		 * BTF, and be fully contained within the verifier.
+		 */
+		info->reg_type = PTR_MAYBE_NULL | PTR_TO_BTF_ID | PTR_TRUSTED;
+		info->btf = btf_vmlinux;
+		info->btf_id = task_struct_type_id;
+
+		return true;
+	}
+
+	return false;
+}
+
+static bool bpf_scx_is_valid_access(int off, int size,
+				    enum bpf_access_type type,
+				    const struct bpf_prog *prog,
+				    struct bpf_insn_access_aux *info)
+{
+	if (type != BPF_READ)
+		return false;
+	if (set_arg_maybe_null("dispatch", 1, off, size, type, prog, info) ||
+	    set_arg_maybe_null("yield", 1, off, size, type, prog, info))
+		return true;
+	if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS)
+		return false;
+	if (off % size != 0)
+		return false;
+
+	return btf_ctx_access(off, size, type, prog, info);
+}
+
+static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
+				     const struct bpf_reg_state *reg, int off,
+				     int size)
+{
+	const struct btf_type *t;
+
+	t = btf_type_by_id(reg->btf, reg->btf_id);
+	if (t == task_struct_type) {
+		if (off >= offsetof(struct task_struct, scx.slice) &&
+		    off + size <= offsetofend(struct task_struct, scx.slice))
+			return SCALAR_VALUE;
+		if (off >= offsetof(struct task_struct, scx.dsq_vtime) &&
+		    off + size <= offsetofend(struct task_struct, scx.dsq_vtime))
+			return SCALAR_VALUE;
+		if (off >= offsetof(struct task_struct, scx.disallow) &&
+		    off + size <= offsetofend(struct task_struct, scx.disallow))
+			return SCALAR_VALUE;
+	}
+
+	return -EACCES;
+}
+
+static const struct bpf_func_proto *
+bpf_scx_get_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
+{
+	switch (func_id) {
+	case BPF_FUNC_task_storage_get:
+		return &bpf_task_storage_get_proto;
+	case BPF_FUNC_task_storage_delete:
+		return &bpf_task_storage_delete_proto;
+	default:
+		return bpf_base_func_proto(func_id, prog);
+	}
+}
+
+static const struct bpf_verifier_ops bpf_scx_verifier_ops = {
+	.get_func_proto = bpf_scx_get_func_proto,
+	.is_valid_access = bpf_scx_is_valid_access,
+	.btf_struct_access = bpf_scx_btf_struct_access,
+};
+
+static int bpf_scx_init_member(const struct btf_type *t,
+			       const struct btf_member *member,
+			       void *kdata, const void *udata)
+{
+	const struct sched_ext_ops *uops = udata;
+	struct sched_ext_ops *ops = kdata;
+	u32 moff = __btf_member_bit_offset(t, member) / 8;
+	int ret;
+
+	switch (moff) {
+	case offsetof(struct sched_ext_ops, dispatch_max_batch):
+		if (*(u32 *)(udata + moff) > INT_MAX)
+			return -E2BIG;
+		ops->dispatch_max_batch = *(u32 *)(udata + moff);
+		return 1;
+	case offsetof(struct sched_ext_ops, flags):
+		if (*(u64 *)(udata + moff) & ~SCX_OPS_ALL_FLAGS)
+			return -EINVAL;
+		ops->flags = *(u64 *)(udata + moff);
+		return 1;
+	case offsetof(struct sched_ext_ops, name):
+		ret = bpf_obj_name_cpy(ops->name, uops->name,
+				       sizeof(ops->name));
+		if (ret < 0)
+			return ret;
+		if (ret == 0)
+			return -EINVAL;
+		return 1;
+	case offsetof(struct sched_ext_ops, timeout_ms):
+		if (msecs_to_jiffies(*(u32 *)(udata + moff)) >
+		    SCX_WATCHDOG_MAX_TIMEOUT)
+			return -E2BIG;
+		ops->timeout_ms = *(u32 *)(udata + moff);
+		return 1;
+	case offsetof(struct sched_ext_ops, exit_dump_len):
+		ops->exit_dump_len =
+			*(u32 *)(udata + moff) ?: SCX_EXIT_DUMP_DFL_LEN;
+		return 1;
+	case offsetof(struct sched_ext_ops, hotplug_seq):
+		ops->hotplug_seq = *(u64 *)(udata + moff);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int bpf_scx_check_member(const struct btf_type *t,
+				const struct btf_member *member,
+				const struct bpf_prog *prog)
+{
+	u32 moff = __btf_member_bit_offset(t, member) / 8;
+
+	switch (moff) {
+	case offsetof(struct sched_ext_ops, init_task):
+	case offsetof(struct sched_ext_ops, cpu_online):
+	case offsetof(struct sched_ext_ops, cpu_offline):
+	case offsetof(struct sched_ext_ops, init):
+	case offsetof(struct sched_ext_ops, exit):
+		break;
+	default:
+		if (prog->sleepable)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int bpf_scx_reg(void *kdata)
+{
+	return scx_ops_enable(kdata);
+}
+
+static void bpf_scx_unreg(void *kdata)
+{
+	scx_ops_disable(SCX_EXIT_UNREG);
+	kthread_flush_work(&scx_ops_disable_work);
+}
+
+static int bpf_scx_init(struct btf *btf)
+{
+	u32 type_id;
+
+	type_id = btf_find_by_name_kind(btf, "task_struct", BTF_KIND_STRUCT);
+	if (type_id < 0)
+		return -EINVAL;
+	task_struct_type = btf_type_by_id(btf, type_id);
+	task_struct_type_id = type_id;
+
+	return 0;
+}
+
+static int bpf_scx_update(void *kdata, void *old_kdata)
+{
+	/*
+	 * sched_ext does not support updating the actively-loaded BPF
+	 * scheduler, as registering a BPF scheduler can always fail if the
+	 * scheduler returns an error code for e.g. ops.init(), ops.init_task(),
+	 * etc. Similarly, we can always race with unregistration happening
+	 * elsewhere, such as with sysrq.
+	 */
+	return -EOPNOTSUPP;
+}
+
+static int bpf_scx_validate(void *kdata)
+{
+	return 0;
+}
+
+static s32 select_cpu_stub(struct task_struct *p, s32 prev_cpu, u64 wake_flags) { return -EINVAL; }
+static void enqueue_stub(struct task_struct *p, u64 enq_flags) {}
+static void dequeue_stub(struct task_struct *p, u64 enq_flags) {}
+static void dispatch_stub(s32 prev_cpu, struct task_struct *p) {}
+static void runnable_stub(struct task_struct *p, u64 enq_flags) {}
+static void running_stub(struct task_struct *p) {}
+static void stopping_stub(struct task_struct *p, bool runnable) {}
+static void quiescent_stub(struct task_struct *p, u64 deq_flags) {}
+static bool yield_stub(struct task_struct *from, struct task_struct *to) { return false; }
+static bool core_sched_before_stub(struct task_struct *a, struct task_struct *b) { return false; }
+static void set_weight_stub(struct task_struct *p, u32 weight) {}
+static void set_cpumask_stub(struct task_struct *p, const struct cpumask *mask) {}
+static void update_idle_stub(s32 cpu, bool idle) {}
+static void cpu_acquire_stub(s32 cpu, struct scx_cpu_acquire_args *args) {}
+static void cpu_release_stub(s32 cpu, struct scx_cpu_release_args *args) {}
+static s32 init_task_stub(struct task_struct *p, struct scx_init_task_args *args) { return -EINVAL; }
+static void exit_task_stub(struct task_struct *p, struct scx_exit_task_args *args) {}
+static void enable_stub(struct task_struct *p) {}
+static void disable_stub(struct task_struct *p) {}
+static void cpu_online_stub(s32 cpu) {}
+static void cpu_offline_stub(s32 cpu) {}
+static s32 init_stub(void) { return -EINVAL; }
+static void exit_stub(struct scx_exit_info *info) {}
+
+static struct sched_ext_ops __bpf_ops_sched_ext_ops = {
+	.select_cpu = select_cpu_stub,
+	.enqueue = enqueue_stub,
+	.dequeue = dequeue_stub,
+	.dispatch = dispatch_stub,
+	.runnable = runnable_stub,
+	.running = running_stub,
+	.stopping = stopping_stub,
+	.quiescent = quiescent_stub,
+	.yield = yield_stub,
+	.core_sched_before = core_sched_before_stub,
+	.set_weight = set_weight_stub,
+	.set_cpumask = set_cpumask_stub,
+	.update_idle = update_idle_stub,
+	.cpu_acquire = cpu_acquire_stub,
+	.cpu_release = cpu_release_stub,
+	.init_task = init_task_stub,
+	.exit_task = exit_task_stub,
+	.enable = enable_stub,
+	.disable = disable_stub,
+	.cpu_online = cpu_online_stub,
+	.cpu_offline = cpu_offline_stub,
+	.init = init_stub,
+	.exit = exit_stub,
+};
+
+static struct bpf_struct_ops bpf_sched_ext_ops = {
+	.verifier_ops = &bpf_scx_verifier_ops,
+	.reg = bpf_scx_reg,
+	.unreg = bpf_scx_unreg,
+	.check_member = bpf_scx_check_member,
+	.init_member = bpf_scx_init_member,
+	.init = bpf_scx_init,
+	.update = bpf_scx_update,
+	.validate = bpf_scx_validate,
+	.name = "sched_ext_ops",
+	.owner = THIS_MODULE,
+	.cfi_stubs = &__bpf_ops_sched_ext_ops
+};
+
+
+/********************************************************************************
+ * System integration and init.
+ */
+
+static void sysrq_handle_sched_ext_reset(u8 key)
+{
+	if (scx_ops_helper)
+		scx_ops_disable(SCX_EXIT_SYSRQ);
+	else
+		pr_info("sched_ext: BPF scheduler not yet used\n");
+}
+
+static const struct sysrq_key_op sysrq_sched_ext_reset_op = {
+	.handler	= sysrq_handle_sched_ext_reset,
+	.help_msg	= "reset-sched-ext(S)",
+	.action_msg	= "Disable sched_ext and revert all tasks to CFS",
+	.enable_mask	= SYSRQ_ENABLE_RTNICE,
+};
+
+static void sysrq_handle_sched_ext_dump(u8 key)
+{
+	struct scx_exit_info ei = { .kind = SCX_EXIT_NONE, .reason = "SysRq-D" };
+
+	if (scx_enabled())
+		scx_dump_state(&ei, 0);
+}
+
+static const struct sysrq_key_op sysrq_sched_ext_dump_op = {
+	.handler	= sysrq_handle_sched_ext_dump,
+	.help_msg	= "dump-sched-ext(D)",
+	.action_msg	= "Trigger sched_ext debug dump",
+	.enable_mask	= SYSRQ_ENABLE_RTNICE,
+};
+
+static bool can_skip_idle_kick(struct rq *rq)
+{
+	lockdep_assert_rq_held(rq);
+
+	/*
+	 * We can skip idle kicking if @rq is going to go through at least one
+	 * full SCX scheduling cycle before going idle. Just checking whether
+	 * curr is not idle is insufficient because we could be racing
+	 * balance_one() trying to pull the next task from a remote rq, which
+	 * may fail, and @rq may become idle afterwards.
+	 *
+	 * The race window is small and we don't and can't guarantee that @rq is
+	 * only kicked while idle anyway. Skip only when sure.
+	 */
+	return !is_idle_task(rq->curr) && !(rq->scx.flags & SCX_RQ_IN_BALANCE);
+}
+
+static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *pseqs)
+{
+	struct rq *rq = cpu_rq(cpu);
+	struct scx_rq *this_scx = &this_rq->scx;
+	bool should_wait = false;
+	unsigned long flags;
+
+	raw_spin_rq_lock_irqsave(rq, flags);
+
+	/*
+	 * During CPU hotplug, a CPU may depend on kicking itself to make
+	 * forward progress. Allow kicking self regardless of online state.
+	 */
+	if (cpu_online(cpu) || cpu == cpu_of(this_rq)) {
+		if (cpumask_test_cpu(cpu, this_scx->cpus_to_preempt)) {
+			if (rq->curr->sched_class == &ext_sched_class)
+				rq->curr->scx.slice = 0;
+			cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt);
+		}
+
+		if (cpumask_test_cpu(cpu, this_scx->cpus_to_wait)) {
+			pseqs[cpu] = rq->scx.pnt_seq;
+			should_wait = true;
+		}
+
+		resched_curr(rq);
+	} else {
+		cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt);
+		cpumask_clear_cpu(cpu, this_scx->cpus_to_wait);
+	}
+
+	raw_spin_rq_unlock_irqrestore(rq, flags);
+
+	return should_wait;
+}
+
+static void kick_one_cpu_if_idle(s32 cpu, struct rq *this_rq)
+{
+	struct rq *rq = cpu_rq(cpu);
+	unsigned long flags;
+
+	raw_spin_rq_lock_irqsave(rq, flags);
+
+	if (!can_skip_idle_kick(rq) &&
+	    (cpu_online(cpu) || cpu == cpu_of(this_rq)))
+		resched_curr(rq);
+
+	raw_spin_rq_unlock_irqrestore(rq, flags);
+}
+
+static void kick_cpus_irq_workfn(struct irq_work *irq_work)
+{
+	struct rq *this_rq = this_rq();
+	struct scx_rq *this_scx = &this_rq->scx;
+	unsigned long *pseqs = this_cpu_ptr(scx_kick_cpus_pnt_seqs);
+	bool should_wait = false;
+	s32 cpu;
+
+	for_each_cpu(cpu, this_scx->cpus_to_kick) {
+		should_wait |= kick_one_cpu(cpu, this_rq, pseqs);
+		cpumask_clear_cpu(cpu, this_scx->cpus_to_kick);
+		cpumask_clear_cpu(cpu, this_scx->cpus_to_kick_if_idle);
+	}
+
+	for_each_cpu(cpu, this_scx->cpus_to_kick_if_idle) {
+		kick_one_cpu_if_idle(cpu, this_rq);
+		cpumask_clear_cpu(cpu, this_scx->cpus_to_kick_if_idle);
+	}
+
+	if (!should_wait)
+		return;
+
+	for_each_cpu(cpu, this_scx->cpus_to_wait) {
+		unsigned long *wait_pnt_seq = &cpu_rq(cpu)->scx.pnt_seq;
+
+		if (cpu != cpu_of(this_rq)) {
+			/*
+			 * Pairs with smp_store_release() issued by this CPU in
+			 * scx_next_task_picked() on the resched path.
+			 *
+			 * We busy-wait here to guarantee that no other task can
+			 * be scheduled on our core before the target CPU has
+			 * entered the resched path.
+			 */
+			while (smp_load_acquire(wait_pnt_seq) == pseqs[cpu])
+				cpu_relax();
+		}
+
+		cpumask_clear_cpu(cpu, this_scx->cpus_to_wait);
+	}
+}
+
+/**
+ * print_scx_info - print out sched_ext scheduler state
+ * @log_lvl: the log level to use when printing
+ * @p: target task
+ *
+ * If a sched_ext scheduler is enabled, print the name and state of the
+ * scheduler. If @p is on sched_ext, print further information about the task.
+ *
+ * This function can be safely called on any task as long as the task_struct
+ * itself is accessible. While safe, this function isn't synchronized and may
+ * print out mixups or garbages of limited length.
+ */
+void print_scx_info(const char *log_lvl, struct task_struct *p)
+{
+	enum scx_ops_enable_state state = scx_ops_enable_state();
+	const char *all = READ_ONCE(scx_switching_all) ? "+all" : "";
+	char runnable_at_buf[22] = "?";
+	struct sched_class *class;
+	unsigned long runnable_at;
+
+	if (state == SCX_OPS_DISABLED)
+		return;
+
+	/*
+	 * Carefully check if the task was running on sched_ext, and then
+	 * carefully copy the time it's been runnable, and its state.
+	 */
+	if (copy_from_kernel_nofault(&class, &p->sched_class, sizeof(class)) ||
+	    class != &ext_sched_class) {
+		printk("%sSched_ext: %s (%s%s)", log_lvl, scx_ops.name,
+		       scx_ops_enable_state_str[state], all);
+		return;
+	}
+
+	if (!copy_from_kernel_nofault(&runnable_at, &p->scx.runnable_at,
+				      sizeof(runnable_at)))
+		scnprintf(runnable_at_buf, sizeof(runnable_at_buf), "%+ldms",
+			  jiffies_delta_msecs(runnable_at, jiffies));
+
+	/* print everything onto one line to conserve console space */
+	printk("%sSched_ext: %s (%s%s), task: runnable_at=%s",
+	       log_lvl, scx_ops.name, scx_ops_enable_state_str[state], all,
+	       runnable_at_buf);
+}
+
+static int scx_pm_handler(struct notifier_block *nb, unsigned long event, void *ptr)
+{
+	/*
+	 * SCX schedulers often have userspace components which are sometimes
+	 * involved in critial scheduling paths. PM operations involve freezing
+	 * userspace which can lead to scheduling misbehaviors including stalls.
+	 * Let's bypass while PM operations are in progress.
+	 */
+	switch (event) {
+	case PM_HIBERNATION_PREPARE:
+	case PM_SUSPEND_PREPARE:
+	case PM_RESTORE_PREPARE:
+		scx_ops_bypass(true);
+		break;
+	case PM_POST_HIBERNATION:
+	case PM_POST_SUSPEND:
+	case PM_POST_RESTORE:
+		scx_ops_bypass(false);
+		break;
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block scx_pm_notifier = {
+	.notifier_call = scx_pm_handler,
+};
+
+void __init init_sched_ext_class(void)
+{
+	s32 cpu, v;
+
+	/*
+	 * The following is to prevent the compiler from optimizing out the enum
+	 * definitions so that BPF scheduler implementations can use them
+	 * through the generated vmlinux.h.
+	 */
+	WRITE_ONCE(v, SCX_ENQ_WAKEUP | SCX_DEQ_SLEEP | SCX_KICK_PREEMPT);
+
+	BUG_ON(rhashtable_init(&dsq_hash, &dsq_hash_params));
+	init_dsq(&scx_dsq_global, SCX_DSQ_GLOBAL);
+#ifdef CONFIG_SMP
+	BUG_ON(!alloc_cpumask_var(&idle_masks.cpu, GFP_KERNEL));
+	BUG_ON(!alloc_cpumask_var(&idle_masks.smt, GFP_KERNEL));
+#endif
+	scx_kick_cpus_pnt_seqs =
+		__alloc_percpu(sizeof(scx_kick_cpus_pnt_seqs[0]) * nr_cpu_ids,
+			       __alignof__(scx_kick_cpus_pnt_seqs[0]));
+	BUG_ON(!scx_kick_cpus_pnt_seqs);
+
+	for_each_possible_cpu(cpu) {
+		struct rq *rq = cpu_rq(cpu);
+
+		init_dsq(&rq->scx.local_dsq, SCX_DSQ_LOCAL);
+		INIT_LIST_HEAD(&rq->scx.runnable_list);
+		INIT_LIST_HEAD(&rq->scx.ddsp_deferred_locals);
+
+		BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_kick, GFP_KERNEL));
+		BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_kick_if_idle, GFP_KERNEL));
+		BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_preempt, GFP_KERNEL));
+		BUG_ON(!zalloc_cpumask_var(&rq->scx.cpus_to_wait, GFP_KERNEL));
+		init_irq_work(&rq->scx.deferred_irq_work, deferred_irq_workfn);
+		init_irq_work(&rq->scx.kick_cpus_irq_work, kick_cpus_irq_workfn);
+
+		if (cpu_online(cpu))
+			cpu_rq(cpu)->scx.flags |= SCX_RQ_ONLINE;
+	}
+
+	register_sysrq_key('S', &sysrq_sched_ext_reset_op);
+	register_sysrq_key('D', &sysrq_sched_ext_dump_op);
+	INIT_DELAYED_WORK(&scx_watchdog_work, scx_watchdog_workfn);
+}
+
+
+/********************************************************************************
+ * Helpers that can be called from the BPF scheduler.
+ */
+#include <linux/btf_ids.h>
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_create_dsq - Create a custom DSQ
+ * @dsq_id: DSQ to create
+ * @node: NUMA node to allocate from
+ *
+ * Create a custom DSQ identified by @dsq_id. Can be called from ops.init() and
+ * ops.init_task().
+ */
+__bpf_kfunc s32 scx_bpf_create_dsq(u64 dsq_id, s32 node)
+{
+	if (!scx_kf_allowed(SCX_KF_SLEEPABLE))
+		return -EINVAL;
+
+	if (unlikely(node >= (int)nr_node_ids ||
+		     (node < 0 && node != NUMA_NO_NODE)))
+		return -EINVAL;
+	return PTR_ERR_OR_ZERO(create_dsq(dsq_id, node));
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(scx_kfunc_ids_sleepable)
+BTF_ID_FLAGS(func, scx_bpf_create_dsq, KF_SLEEPABLE)
+BTF_KFUNCS_END(scx_kfunc_ids_sleepable)
+
+static const struct btf_kfunc_id_set scx_kfunc_set_sleepable = {
+	.owner			= THIS_MODULE,
+	.set			= &scx_kfunc_ids_sleepable,
+};
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_select_cpu_dfl - The default implementation of ops.select_cpu()
+ * @p: task_struct to select a CPU for
+ * @prev_cpu: CPU @p was on previously
+ * @wake_flags: %SCX_WAKE_* flags
+ * @is_idle: out parameter indicating whether the returned CPU is idle
+ *
+ * Can only be called from ops.select_cpu() if the built-in CPU selection is
+ * enabled - ops.update_idle() is missing or %SCX_OPS_KEEP_BUILTIN_IDLE is set.
+ * @p, @prev_cpu and @wake_flags match ops.select_cpu().
+ *
+ * Returns the picked CPU with *@is_idle indicating whether the picked CPU is
+ * currently idle and thus a good candidate for direct dispatching.
+ */
+__bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
+				       u64 wake_flags, bool *is_idle)
+{
+	if (!scx_kf_allowed(SCX_KF_SELECT_CPU)) {
+		*is_idle = false;
+		return prev_cpu;
+	}
+#ifdef CONFIG_SMP
+	return scx_select_cpu_dfl(p, prev_cpu, wake_flags, is_idle);
+#else
+	*is_idle = false;
+	return prev_cpu;
+#endif
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(scx_kfunc_ids_select_cpu)
+BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_RCU)
+BTF_KFUNCS_END(scx_kfunc_ids_select_cpu)
+
+static const struct btf_kfunc_id_set scx_kfunc_set_select_cpu = {
+	.owner			= THIS_MODULE,
+	.set			= &scx_kfunc_ids_select_cpu,
+};
+
+static bool scx_dispatch_preamble(struct task_struct *p, u64 enq_flags)
+{
+	if (!scx_kf_allowed(SCX_KF_ENQUEUE | SCX_KF_DISPATCH))
+		return false;
+
+	lockdep_assert_irqs_disabled();
+
+	if (unlikely(!p)) {
+		scx_ops_error("called with NULL task");
+		return false;
+	}
+
+	if (unlikely(enq_flags & __SCX_ENQ_INTERNAL_MASK)) {
+		scx_ops_error("invalid enq_flags 0x%llx", enq_flags);
+		return false;
+	}
+
+	return true;
+}
+
+static void scx_dispatch_commit(struct task_struct *p, u64 dsq_id, u64 enq_flags)
+{
+	struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
+	struct task_struct *ddsp_task;
+
+	ddsp_task = __this_cpu_read(direct_dispatch_task);
+	if (ddsp_task) {
+		mark_direct_dispatch(ddsp_task, p, dsq_id, enq_flags);
+		return;
+	}
+
+	if (unlikely(dspc->cursor >= scx_dsp_max_batch)) {
+		scx_ops_error("dispatch buffer overflow");
+		return;
+	}
+
+	dspc->buf[dspc->cursor++] = (struct scx_dsp_buf_ent){
+		.task = p,
+		.qseq = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_QSEQ_MASK,
+		.dsq_id = dsq_id,
+		.enq_flags = enq_flags,
+	};
+}
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_dispatch - Dispatch a task into the FIFO queue of a DSQ
+ * @p: task_struct to dispatch
+ * @dsq_id: DSQ to dispatch to
+ * @slice: duration @p can run for in nsecs
+ * @enq_flags: SCX_ENQ_*
+ *
+ * Dispatch @p into the FIFO queue of the DSQ identified by @dsq_id. It is safe
+ * to call this function spuriously. Can be called from ops.enqueue(),
+ * ops.select_cpu(), and ops.dispatch().
+ *
+ * When called from ops.select_cpu() or ops.enqueue(), it's for direct dispatch
+ * and @p must match the task being enqueued. Also, %SCX_DSQ_LOCAL_ON can't be
+ * used to target the local DSQ of a CPU other than the enqueueing one. Use
+ * ops.select_cpu() to be on the target CPU in the first place.
+ *
+ * When called from ops.select_cpu(), @enq_flags and @dsp_id are stored, and @p
+ * will be directly dispatched to the corresponding dispatch queue after
+ * ops.select_cpu() returns. If @p is dispatched to SCX_DSQ_LOCAL, it will be
+ * dispatched to the local DSQ of the CPU returned by ops.select_cpu().
+ * @enq_flags are OR'd with the enqueue flags on the enqueue path before the
+ * task is dispatched.
+ *
+ * When called from ops.dispatch(), there are no restrictions on @p or @dsq_id
+ * and this function can be called upto ops.dispatch_max_batch times to dispatch
+ * multiple tasks. scx_bpf_dispatch_nr_slots() returns the number of the
+ * remaining slots. scx_bpf_consume() flushes the batch and resets the counter.
+ *
+ * This function doesn't have any locking restrictions and may be called under
+ * BPF locks (in the future when BPF introduces more flexible locking).
+ *
+ * @p is allowed to run for @slice. The scheduling path is triggered on slice
+ * exhaustion. If zero, the current residual slice is maintained. If
+ * %SCX_SLICE_INF, @p never expires and the BPF scheduler must kick the CPU with
+ * scx_bpf_kick_cpu() to trigger scheduling.
+ */
+__bpf_kfunc void scx_bpf_dispatch(struct task_struct *p, u64 dsq_id, u64 slice,
+				  u64 enq_flags)
+{
+	if (!scx_dispatch_preamble(p, enq_flags))
+		return;
+
+	if (slice)
+		p->scx.slice = slice;
+	else
+		p->scx.slice = p->scx.slice ?: 1;
+
+	scx_dispatch_commit(p, dsq_id, enq_flags);
+}
+
+/**
+ * scx_bpf_dispatch_vtime - Dispatch a task into the vtime priority queue of a DSQ
+ * @p: task_struct to dispatch
+ * @dsq_id: DSQ to dispatch to
+ * @slice: duration @p can run for in nsecs
+ * @vtime: @p's ordering inside the vtime-sorted queue of the target DSQ
+ * @enq_flags: SCX_ENQ_*
+ *
+ * Dispatch @p into the vtime priority queue of the DSQ identified by @dsq_id.
+ * Tasks queued into the priority queue are ordered by @vtime and always
+ * consumed after the tasks in the FIFO queue. All other aspects are identical
+ * to scx_bpf_dispatch().
+ *
+ * @vtime ordering is according to time_before64() which considers wrapping. A
+ * numerically larger vtime may indicate an earlier position in the ordering and
+ * vice-versa.
+ */
+__bpf_kfunc void scx_bpf_dispatch_vtime(struct task_struct *p, u64 dsq_id,
+					u64 slice, u64 vtime, u64 enq_flags)
+{
+	if (!scx_dispatch_preamble(p, enq_flags))
+		return;
+
+	if (slice)
+		p->scx.slice = slice;
+	else
+		p->scx.slice = p->scx.slice ?: 1;
+
+	p->scx.dsq_vtime = vtime;
+
+	scx_dispatch_commit(p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ);
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch)
+BTF_ID_FLAGS(func, scx_bpf_dispatch, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_dispatch_vtime, KF_RCU)
+BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch)
+
+static const struct btf_kfunc_id_set scx_kfunc_set_enqueue_dispatch = {
+	.owner			= THIS_MODULE,
+	.set			= &scx_kfunc_ids_enqueue_dispatch,
+};
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_dispatch_nr_slots - Return the number of remaining dispatch slots
+ *
+ * Can only be called from ops.dispatch().
+ */
+__bpf_kfunc u32 scx_bpf_dispatch_nr_slots(void)
+{
+	if (!scx_kf_allowed(SCX_KF_DISPATCH))
+		return 0;
+
+	return scx_dsp_max_batch - __this_cpu_read(scx_dsp_ctx->cursor);
+}
+
+/**
+ * scx_bpf_dispatch_cancel - Cancel the latest dispatch
+ *
+ * Cancel the latest dispatch. Can be called multiple times to cancel further
+ * dispatches. Can only be called from ops.dispatch().
+ */
+__bpf_kfunc void scx_bpf_dispatch_cancel(void)
+{
+	struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
+
+	if (!scx_kf_allowed(SCX_KF_DISPATCH))
+		return;
+
+	if (dspc->cursor > 0)
+		dspc->cursor--;
+	else
+		scx_ops_error("dispatch buffer underflow");
+}
+
+/**
+ * scx_bpf_consume - Transfer a task from a DSQ to the current CPU's local DSQ
+ * @dsq_id: DSQ to consume
+ *
+ * Consume a task from the non-local DSQ identified by @dsq_id and transfer it
+ * to the current CPU's local DSQ for execution. Can only be called from
+ * ops.dispatch().
+ *
+ * This function flushes the in-flight dispatches from scx_bpf_dispatch() before
+ * trying to consume the specified DSQ. It may also grab rq locks and thus can't
+ * be called under any BPF locks.
+ *
+ * Returns %true if a task has been consumed, %false if there isn't any task to
+ * consume.
+ */
+__bpf_kfunc bool scx_bpf_consume(u64 dsq_id)
+{
+	struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
+	struct scx_dispatch_q *dsq;
+
+	if (!scx_kf_allowed(SCX_KF_DISPATCH))
+		return false;
+
+	flush_dispatch_buf(dspc->rq);
+
+	dsq = find_non_local_dsq(dsq_id);
+	if (unlikely(!dsq)) {
+		scx_ops_error("invalid DSQ ID 0x%016llx", dsq_id);
+		return false;
+	}
+
+	if (consume_dispatch_q(dspc->rq, dsq)) {
+		/*
+		 * A successfully consumed task can be dequeued before it starts
+		 * running while the CPU is trying to migrate other dispatched
+		 * tasks. Bump nr_tasks to tell balance_scx() to retry on empty
+		 * local DSQ.
+		 */
+		dspc->nr_tasks++;
+		return true;
+	} else {
+		return false;
+	}
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(scx_kfunc_ids_dispatch)
+BTF_ID_FLAGS(func, scx_bpf_dispatch_nr_slots)
+BTF_ID_FLAGS(func, scx_bpf_dispatch_cancel)
+BTF_ID_FLAGS(func, scx_bpf_consume)
+BTF_KFUNCS_END(scx_kfunc_ids_dispatch)
+
+static const struct btf_kfunc_id_set scx_kfunc_set_dispatch = {
+	.owner			= THIS_MODULE,
+	.set			= &scx_kfunc_ids_dispatch,
+};
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ
+ *
+ * Iterate over all of the tasks currently enqueued on the local DSQ of the
+ * caller's CPU, and re-enqueue them in the BPF scheduler. Returns the number of
+ * processed tasks. Can only be called from ops.cpu_release().
+ */
+__bpf_kfunc u32 scx_bpf_reenqueue_local(void)
+{
+	LIST_HEAD(tasks);
+	u32 nr_enqueued = 0;
+	struct rq *rq;
+	struct task_struct *p, *n;
+
+	if (!scx_kf_allowed(SCX_KF_CPU_RELEASE))
+		return 0;
+
+	rq = cpu_rq(smp_processor_id());
+	lockdep_assert_rq_held(rq);
+
+	/*
+	 * The BPF scheduler may choose to dispatch tasks back to
+	 * @rq->scx.local_dsq. Move all candidate tasks off to a private list
+	 * first to avoid processing the same tasks repeatedly.
+	 */
+	list_for_each_entry_safe(p, n, &rq->scx.local_dsq.list,
+				 scx.dsq_list.node) {
+		/*
+		 * If @p is being migrated, @p's current CPU may not agree with
+		 * its allowed CPUs and the migration_cpu_stop is about to
+		 * deactivate and re-activate @p anyway. Skip re-enqueueing.
+		 *
+		 * While racing sched property changes may also dequeue and
+		 * re-enqueue a migrating task while its current CPU and allowed
+		 * CPUs disagree, they use %ENQUEUE_RESTORE which is bypassed to
+		 * the current local DSQ for running tasks and thus are not
+		 * visible to the BPF scheduler.
+		 */
+		if (p->migration_pending)
+			continue;
+
+		dispatch_dequeue(rq, p);
+		list_add_tail(&p->scx.dsq_list.node, &tasks);
+	}
+
+	list_for_each_entry_safe(p, n, &tasks, scx.dsq_list.node) {
+		list_del_init(&p->scx.dsq_list.node);
+		do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1);
+		nr_enqueued++;
+	}
+
+	return nr_enqueued;
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(scx_kfunc_ids_cpu_release)
+BTF_ID_FLAGS(func, scx_bpf_reenqueue_local)
+BTF_KFUNCS_END(scx_kfunc_ids_cpu_release)
+
+static const struct btf_kfunc_id_set scx_kfunc_set_cpu_release = {
+	.owner			= THIS_MODULE,
+	.set			= &scx_kfunc_ids_cpu_release,
+};
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_kick_cpu - Trigger reschedule on a CPU
+ * @cpu: cpu to kick
+ * @flags: %SCX_KICK_* flags
+ *
+ * Kick @cpu into rescheduling. This can be used to wake up an idle CPU or
+ * trigger rescheduling on a busy CPU. This can be called from any online
+ * scx_ops operation and the actual kicking is performed asynchronously through
+ * an irq work.
+ */
+__bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags)
+{
+	struct rq *this_rq;
+	unsigned long irq_flags;
+
+	if (!ops_cpu_valid(cpu, NULL))
+		return;
+
+	/*
+	 * While bypassing for PM ops, IRQ handling may not be online which can
+	 * lead to irq_work_queue() malfunction such as infinite busy wait for
+	 * IRQ status update. Suppress kicking.
+	 */
+	if (scx_ops_bypassing())
+		return;
+
+	local_irq_save(irq_flags);
+
+	this_rq = this_rq();
+
+	/*
+	 * Actual kicking is bounced to kick_cpus_irq_workfn() to avoid nesting
+	 * rq locks. We can probably be smarter and avoid bouncing if called
+	 * from ops which don't hold a rq lock.
+	 */
+	if (flags & SCX_KICK_IDLE) {
+		struct rq *target_rq = cpu_rq(cpu);
+
+		if (unlikely(flags & (SCX_KICK_PREEMPT | SCX_KICK_WAIT)))
+			scx_ops_error("PREEMPT/WAIT cannot be used with SCX_KICK_IDLE");
+
+		if (raw_spin_rq_trylock(target_rq)) {
+			if (can_skip_idle_kick(target_rq)) {
+				raw_spin_rq_unlock(target_rq);
+				goto out;
+			}
+			raw_spin_rq_unlock(target_rq);
+		}
+		cpumask_set_cpu(cpu, this_rq->scx.cpus_to_kick_if_idle);
+	} else {
+		cpumask_set_cpu(cpu, this_rq->scx.cpus_to_kick);
+
+		if (flags & SCX_KICK_PREEMPT)
+			cpumask_set_cpu(cpu, this_rq->scx.cpus_to_preempt);
+		if (flags & SCX_KICK_WAIT)
+			cpumask_set_cpu(cpu, this_rq->scx.cpus_to_wait);
+	}
+
+	irq_work_queue(&this_rq->scx.kick_cpus_irq_work);
+out:
+	local_irq_restore(irq_flags);
+}
+
+/**
+ * scx_bpf_dsq_nr_queued - Return the number of queued tasks
+ * @dsq_id: id of the DSQ
+ *
+ * Return the number of tasks in the DSQ matching @dsq_id. If not found,
+ * -%ENOENT is returned.
+ */
+__bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id)
+{
+	struct scx_dispatch_q *dsq;
+	s32 ret;
+
+	preempt_disable();
+
+	if (dsq_id == SCX_DSQ_LOCAL) {
+		ret = READ_ONCE(this_rq()->scx.local_dsq.nr);
+		goto out;
+	} else if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) {
+		s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK;
+
+		if (ops_cpu_valid(cpu, NULL)) {
+			ret = READ_ONCE(cpu_rq(cpu)->scx.local_dsq.nr);
+			goto out;
+		}
+	} else {
+		dsq = find_non_local_dsq(dsq_id);
+		if (dsq) {
+			ret = READ_ONCE(dsq->nr);
+			goto out;
+		}
+	}
+	ret = -ENOENT;
+out:
+	preempt_enable();
+	return ret;
+}
+
+/**
+ * scx_bpf_destroy_dsq - Destroy a custom DSQ
+ * @dsq_id: DSQ to destroy
+ *
+ * Destroy the custom DSQ identified by @dsq_id. Only DSQs created with
+ * scx_bpf_create_dsq() can be destroyed. The caller must ensure that the DSQ is
+ * empty and no further tasks are dispatched to it. Ignored if called on a DSQ
+ * which doesn't exist. Can be called from any online scx_ops operations.
+ */
+__bpf_kfunc void scx_bpf_destroy_dsq(u64 dsq_id)
+{
+	destroy_dsq(dsq_id);
+}
+
+/**
+ * bpf_iter_scx_dsq_new - Create a DSQ iterator
+ * @it: iterator to initialize
+ * @dsq_id: DSQ to iterate
+ * @flags: %SCX_DSQ_ITER_*
+ *
+ * Initialize BPF iterator @it which can be used with bpf_for_each() to walk
+ * tasks in the DSQ specified by @dsq_id. Iteration using @it only includes
+ * tasks which are already queued when this function is invoked.
+ */
+__bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id,
+				     u64 flags)
+{
+	struct bpf_iter_scx_dsq_kern *kit = (void *)it;
+
+	BUILD_BUG_ON(sizeof(struct bpf_iter_scx_dsq_kern) >
+		     sizeof(struct bpf_iter_scx_dsq));
+	BUILD_BUG_ON(__alignof__(struct bpf_iter_scx_dsq_kern) !=
+		     __alignof__(struct bpf_iter_scx_dsq));
+
+	if (flags & ~__SCX_DSQ_ITER_ALL_FLAGS)
+		return -EINVAL;
+
+	kit->dsq = find_non_local_dsq(dsq_id);
+	if (!kit->dsq)
+		return -ENOENT;
+
+	INIT_LIST_HEAD(&kit->cursor.node);
+	kit->cursor.is_bpf_iter_cursor = true;
+	kit->dsq_seq = READ_ONCE(kit->dsq->seq);
+	kit->flags = flags;
+
+	return 0;
+}
+
+/**
+ * bpf_iter_scx_dsq_next - Progress a DSQ iterator
+ * @it: iterator to progress
+ *
+ * Return the next task. See bpf_iter_scx_dsq_new().
+ */
+__bpf_kfunc struct task_struct *bpf_iter_scx_dsq_next(struct bpf_iter_scx_dsq *it)
+{
+	struct bpf_iter_scx_dsq_kern *kit = (void *)it;
+	bool rev = kit->flags & SCX_DSQ_ITER_REV;
+	struct task_struct *p;
+	unsigned long flags;
+
+	if (!kit->dsq)
+		return NULL;
+
+	raw_spin_lock_irqsave(&kit->dsq->lock, flags);
+
+	if (list_empty(&kit->cursor.node))
+		p = NULL;
+	else
+		p = container_of(&kit->cursor, struct task_struct, scx.dsq_list);
+
+	/*
+	 * Only tasks which were queued before the iteration started are
+	 * visible. This bounds BPF iterations and guarantees that vtime never
+	 * jumps in the other direction while iterating.
+	 */
+	do {
+		p = nldsq_next_task(kit->dsq, p, rev);
+	} while (p && unlikely(u32_before(kit->dsq_seq, p->scx.dsq_seq)));
+
+	if (p) {
+		if (rev)
+			list_move_tail(&kit->cursor.node, &p->scx.dsq_list.node);
+		else
+			list_move(&kit->cursor.node, &p->scx.dsq_list.node);
+	} else {
+		list_del_init(&kit->cursor.node);
+	}
+
+	raw_spin_unlock_irqrestore(&kit->dsq->lock, flags);
+
+	return p;
+}
+
+/**
+ * bpf_iter_scx_dsq_destroy - Destroy a DSQ iterator
+ * @it: iterator to destroy
+ *
+ * Undo scx_iter_scx_dsq_new().
+ */
+__bpf_kfunc void bpf_iter_scx_dsq_destroy(struct bpf_iter_scx_dsq *it)
+{
+	struct bpf_iter_scx_dsq_kern *kit = (void *)it;
+
+	if (!kit->dsq)
+		return;
+
+	if (!list_empty(&kit->cursor.node)) {
+		unsigned long flags;
+
+		raw_spin_lock_irqsave(&kit->dsq->lock, flags);
+		list_del_init(&kit->cursor.node);
+		raw_spin_unlock_irqrestore(&kit->dsq->lock, flags);
+	}
+	kit->dsq = NULL;
+}
+
+__bpf_kfunc_end_defs();
+
+static s32 __bstr_format(u64 *data_buf, char *line_buf, size_t line_size,
+			 char *fmt, unsigned long long *data, u32 data__sz)
+{
+	struct bpf_bprintf_data bprintf_data = { .get_bin_args = true };
+	s32 ret;
+
+	if (data__sz % 8 || data__sz > MAX_BPRINTF_VARARGS * 8 ||
+	    (data__sz && !data)) {
+		scx_ops_error("invalid data=%p and data__sz=%u",
+			      (void *)data, data__sz);
+		return -EINVAL;
+	}
+
+	ret = copy_from_kernel_nofault(data_buf, data, data__sz);
+	if (ret < 0) {
+		scx_ops_error("failed to read data fields (%d)", ret);
+		return ret;
+	}
+
+	ret = bpf_bprintf_prepare(fmt, UINT_MAX, data_buf, data__sz / 8,
+				  &bprintf_data);
+	if (ret < 0) {
+		scx_ops_error("format preparation failed (%d)", ret);
+		return ret;
+	}
+
+	ret = bstr_printf(line_buf, line_size, fmt,
+			  bprintf_data.bin_args);
+	bpf_bprintf_cleanup(&bprintf_data);
+	if (ret < 0) {
+		scx_ops_error("(\"%s\", %p, %u) failed to format",
+			      fmt, data, data__sz);
+		return ret;
+	}
+
+	return ret;
+}
+
+static s32 bstr_format(struct scx_bstr_buf *buf,
+		       char *fmt, unsigned long long *data, u32 data__sz)
+{
+	return __bstr_format(buf->data, buf->line, sizeof(buf->line),
+			     fmt, data, data__sz);
+}
+
+__bpf_kfunc_start_defs();
+
+/**
+ * scx_bpf_exit_bstr - Gracefully exit the BPF scheduler.
+ * @exit_code: Exit value to pass to user space via struct scx_exit_info.
+ * @fmt: error message format string
+ * @data: format string parameters packaged using ___bpf_fill() macro
+ * @data__sz: @data len, must end in '__sz' for the verifier
+ *
+ * Indicate that the BPF scheduler wants to exit gracefully, and initiate ops
+ * disabling.
+ */
+__bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt,
+				   unsigned long long *data, u32 data__sz)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags);
+	if (bstr_format(&scx_exit_bstr_buf, fmt, data, data__sz) >= 0)
+		scx_ops_exit_kind(SCX_EXIT_UNREG_BPF, exit_code, "%s",
+				  scx_exit_bstr_buf.line);
+	raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags);
+}
+
+/**
+ * scx_bpf_error_bstr - Indicate fatal error
+ * @fmt: error message format string
+ * @data: format string parameters packaged using ___bpf_fill() macro
+ * @data__sz: @data len, must end in '__sz' for the verifier
+ *
+ * Indicate that the BPF scheduler encountered a fatal error and initiate ops
+ * disabling.
+ */
+__bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data,
+				    u32 data__sz)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags);
+	if (bstr_format(&scx_exit_bstr_buf, fmt, data, data__sz) >= 0)
+		scx_ops_exit_kind(SCX_EXIT_ERROR_BPF, 0, "%s",
+				  scx_exit_bstr_buf.line);
+	raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags);
+}
+
+/**
+ * scx_bpf_dump - Generate extra debug dump specific to the BPF scheduler
+ * @fmt: format string
+ * @data: format string parameters packaged using ___bpf_fill() macro
+ * @data__sz: @data len, must end in '__sz' for the verifier
+ *
+ * To be called through scx_bpf_dump() helper from ops.dump(), dump_cpu() and
+ * dump_task() to generate extra debug dump specific to the BPF scheduler.
+ *
+ * The extra dump may be multiple lines. A single line may be split over
+ * multiple calls. The last line is automatically terminated.
+ */
+__bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data,
+				   u32 data__sz)
+{
+	struct scx_dump_data *dd = &scx_dump_data;
+	struct scx_bstr_buf *buf = &dd->buf;
+	s32 ret;
+
+	if (raw_smp_processor_id() != dd->cpu) {
+		scx_ops_error("scx_bpf_dump() must only be called from ops.dump() and friends");
+		return;
+	}
+
+	/* append the formatted string to the line buf */
+	ret = __bstr_format(buf->data, buf->line + dd->cursor,
+			    sizeof(buf->line) - dd->cursor, fmt, data, data__sz);
+	if (ret < 0) {
+		dump_line(dd->s, "%s[!] (\"%s\", %p, %u) failed to format (%d)",
+			  dd->prefix, fmt, data, data__sz, ret);
+		return;
+	}
+
+	dd->cursor += ret;
+	dd->cursor = min_t(s32, dd->cursor, sizeof(buf->line));
+
+	if (!dd->cursor)
+		return;
+
+	/*
+	 * If the line buf overflowed or ends in a newline, flush it into the
+	 * dump. This is to allow the caller to generate a single line over
+	 * multiple calls. As ops_dump_flush() can also handle multiple lines in
+	 * the line buf, the only case which can lead to an unexpected
+	 * truncation is when the caller keeps generating newlines in the middle
+	 * instead of the end consecutively. Don't do that.
+	 */
+	if (dd->cursor >= sizeof(buf->line) || buf->line[dd->cursor - 1] == '\n')
+		ops_dump_flush();
+}
+
+/**
+ * scx_bpf_cpuperf_cap - Query the maximum relative capacity of a CPU
+ * @cpu: CPU of interest
+ *
+ * Return the maximum relative capacity of @cpu in relation to the most
+ * performant CPU in the system. The return value is in the range [1,
+ * %SCX_CPUPERF_ONE]. See scx_bpf_cpuperf_cur().
+ */
+__bpf_kfunc u32 scx_bpf_cpuperf_cap(s32 cpu)
+{
+	if (ops_cpu_valid(cpu, NULL))
+		return arch_scale_cpu_capacity(cpu);
+	else
+		return SCX_CPUPERF_ONE;
+}
+
+/**
+ * scx_bpf_cpuperf_cur - Query the current relative performance of a CPU
+ * @cpu: CPU of interest
+ *
+ * Return the current relative performance of @cpu in relation to its maximum.
+ * The return value is in the range [1, %SCX_CPUPERF_ONE].
+ *
+ * The current performance level of a CPU in relation to the maximum performance
+ * available in the system can be calculated as follows:
+ *
+ *   scx_bpf_cpuperf_cap() * scx_bpf_cpuperf_cur() / %SCX_CPUPERF_ONE
+ *
+ * The result is in the range [1, %SCX_CPUPERF_ONE].
+ */
+__bpf_kfunc u32 scx_bpf_cpuperf_cur(s32 cpu)
+{
+	if (ops_cpu_valid(cpu, NULL))
+		return arch_scale_freq_capacity(cpu);
+	else
+		return SCX_CPUPERF_ONE;
+}
+
+/**
+ * scx_bpf_cpuperf_set - Set the relative performance target of a CPU
+ * @cpu: CPU of interest
+ * @perf: target performance level [0, %SCX_CPUPERF_ONE]
+ * @flags: %SCX_CPUPERF_* flags
+ *
+ * Set the target performance level of @cpu to @perf. @perf is in linear
+ * relative scale between 0 and %SCX_CPUPERF_ONE. This determines how the
+ * schedutil cpufreq governor chooses the target frequency.
+ *
+ * The actual performance level chosen, CPU grouping, and the overhead and
+ * latency of the operations are dependent on the hardware and cpufreq driver in
+ * use. Consult hardware and cpufreq documentation for more information. The
+ * current performance level can be monitored using scx_bpf_cpuperf_cur().
+ */
+__bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf)
+{
+	if (unlikely(perf > SCX_CPUPERF_ONE)) {
+		scx_ops_error("Invalid cpuperf target %u for CPU %d", perf, cpu);
+		return;
+	}
+
+	if (ops_cpu_valid(cpu, NULL)) {
+		struct rq *rq = cpu_rq(cpu);
+
+		rq->scx.cpuperf_target = perf;
+
+		rcu_read_lock_sched_notrace();
+		cpufreq_update_util(cpu_rq(cpu), 0);
+		rcu_read_unlock_sched_notrace();
+	}
+}
+
+/**
+ * scx_bpf_nr_cpu_ids - Return the number of possible CPU IDs
+ *
+ * All valid CPU IDs in the system are smaller than the returned value.
+ */
+__bpf_kfunc u32 scx_bpf_nr_cpu_ids(void)
+{
+	return nr_cpu_ids;
+}
+
+/**
+ * scx_bpf_get_possible_cpumask - Get a referenced kptr to cpu_possible_mask
+ */
+__bpf_kfunc const struct cpumask *scx_bpf_get_possible_cpumask(void)
+{
+	return cpu_possible_mask;
+}
+
+/**
+ * scx_bpf_get_online_cpumask - Get a referenced kptr to cpu_online_mask
+ */
+__bpf_kfunc const struct cpumask *scx_bpf_get_online_cpumask(void)
+{
+	return cpu_online_mask;
+}
+
+/**
+ * scx_bpf_put_cpumask - Release a possible/online cpumask
+ * @cpumask: cpumask to release
+ */
+__bpf_kfunc void scx_bpf_put_cpumask(const struct cpumask *cpumask)
+{
+	/*
+	 * Empty function body because we aren't actually acquiring or releasing
+	 * a reference to a global cpumask, which is read-only in the caller and
+	 * is never released. The acquire / release semantics here are just used
+	 * to make the cpumask is a trusted pointer in the caller.
+	 */
+}
+
+/**
+ * scx_bpf_get_idle_cpumask - Get a referenced kptr to the idle-tracking
+ * per-CPU cpumask.
+ *
+ * Returns NULL if idle tracking is not enabled, or running on a UP kernel.
+ */
+__bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
+{
+	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
+		scx_ops_error("built-in idle tracking is disabled");
+		return cpu_none_mask;
+	}
+
+#ifdef CONFIG_SMP
+	return idle_masks.cpu;
+#else
+	return cpu_none_mask;
+#endif
+}
+
+/**
+ * scx_bpf_get_idle_smtmask - Get a referenced kptr to the idle-tracking,
+ * per-physical-core cpumask. Can be used to determine if an entire physical
+ * core is free.
+ *
+ * Returns NULL if idle tracking is not enabled, or running on a UP kernel.
+ */
+__bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask(void)
+{
+	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
+		scx_ops_error("built-in idle tracking is disabled");
+		return cpu_none_mask;
+	}
+
+#ifdef CONFIG_SMP
+	if (sched_smt_active())
+		return idle_masks.smt;
+	else
+		return idle_masks.cpu;
+#else
+	return cpu_none_mask;
+#endif
+}
+
+/**
+ * scx_bpf_put_idle_cpumask - Release a previously acquired referenced kptr to
+ * either the percpu, or SMT idle-tracking cpumask.
+ */
+__bpf_kfunc void scx_bpf_put_idle_cpumask(const struct cpumask *idle_mask)
+{
+	/*
+	 * Empty function body because we aren't actually acquiring or releasing
+	 * a reference to a global idle cpumask, which is read-only in the
+	 * caller and is never released. The acquire / release semantics here
+	 * are just used to make the cpumask a trusted pointer in the caller.
+	 */
+}
+
+/**
+ * scx_bpf_test_and_clear_cpu_idle - Test and clear @cpu's idle state
+ * @cpu: cpu to test and clear idle for
+ *
+ * Returns %true if @cpu was idle and its idle state was successfully cleared.
+ * %false otherwise.
+ *
+ * Unavailable if ops.update_idle() is implemented and
+ * %SCX_OPS_KEEP_BUILTIN_IDLE is not set.
+ */
+__bpf_kfunc bool scx_bpf_test_and_clear_cpu_idle(s32 cpu)
+{
+	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
+		scx_ops_error("built-in idle tracking is disabled");
+		return false;
+	}
+
+	if (ops_cpu_valid(cpu, NULL))
+		return test_and_clear_cpu_idle(cpu);
+	else
+		return false;
+}
+
+/**
+ * scx_bpf_pick_idle_cpu - Pick and claim an idle cpu
+ * @cpus_allowed: Allowed cpumask
+ * @flags: %SCX_PICK_IDLE_CPU_* flags
+ *
+ * Pick and claim an idle cpu in @cpus_allowed. Returns the picked idle cpu
+ * number on success. -%EBUSY if no matching cpu was found.
+ *
+ * Idle CPU tracking may race against CPU scheduling state transitions. For
+ * example, this function may return -%EBUSY as CPUs are transitioning into the
+ * idle state. If the caller then assumes that there will be dispatch events on
+ * the CPUs as they were all busy, the scheduler may end up stalling with CPUs
+ * idling while there are pending tasks. Use scx_bpf_pick_any_cpu() and
+ * scx_bpf_kick_cpu() to guarantee that there will be at least one dispatch
+ * event in the near future.
+ *
+ * Unavailable if ops.update_idle() is implemented and
+ * %SCX_OPS_KEEP_BUILTIN_IDLE is not set.
+ */
+__bpf_kfunc s32 scx_bpf_pick_idle_cpu(const struct cpumask *cpus_allowed,
+				      u64 flags)
+{
+	if (!static_branch_likely(&scx_builtin_idle_enabled)) {
+		scx_ops_error("built-in idle tracking is disabled");
+		return -EBUSY;
+	}
+
+	return scx_pick_idle_cpu(cpus_allowed, flags);
+}
+
+/**
+ * scx_bpf_pick_any_cpu - Pick and claim an idle cpu if available or pick any CPU
+ * @cpus_allowed: Allowed cpumask
+ * @flags: %SCX_PICK_IDLE_CPU_* flags
+ *
+ * Pick and claim an idle cpu in @cpus_allowed. If none is available, pick any
+ * CPU in @cpus_allowed. Guaranteed to succeed and returns the picked idle cpu
+ * number if @cpus_allowed is not empty. -%EBUSY is returned if @cpus_allowed is
+ * empty.
+ *
+ * If ops.update_idle() is implemented and %SCX_OPS_KEEP_BUILTIN_IDLE is not
+ * set, this function can't tell which CPUs are idle and will always pick any
+ * CPU.
+ */
+__bpf_kfunc s32 scx_bpf_pick_any_cpu(const struct cpumask *cpus_allowed,
+				     u64 flags)
+{
+	s32 cpu;
+
+	if (static_branch_likely(&scx_builtin_idle_enabled)) {
+		cpu = scx_pick_idle_cpu(cpus_allowed, flags);
+		if (cpu >= 0)
+			return cpu;
+	}
+
+	cpu = cpumask_any_distribute(cpus_allowed);
+	if (cpu < nr_cpu_ids)
+		return cpu;
+	else
+		return -EBUSY;
+}
+
+/**
+ * scx_bpf_task_running - Is task currently running?
+ * @p: task of interest
+ */
+__bpf_kfunc bool scx_bpf_task_running(const struct task_struct *p)
+{
+	return task_rq(p)->curr == p;
+}
+
+/**
+ * scx_bpf_task_cpu - CPU a task is currently associated with
+ * @p: task of interest
+ */
+__bpf_kfunc s32 scx_bpf_task_cpu(const struct task_struct *p)
+{
+	return task_cpu(p);
+}
+
+/**
+ * scx_bpf_cpu_rq - Fetch the rq of a CPU
+ * @cpu: CPU of the rq
+ */
+__bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu)
+{
+	if (!ops_cpu_valid(cpu, NULL))
+		return NULL;
+
+	return cpu_rq(cpu);
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(scx_kfunc_ids_any)
+BTF_ID_FLAGS(func, scx_bpf_kick_cpu)
+BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued)
+BTF_ID_FLAGS(func, scx_bpf_destroy_dsq)
+BTF_ID_FLAGS(func, bpf_iter_scx_dsq_new, KF_ITER_NEW | KF_RCU_PROTECTED)
+BTF_ID_FLAGS(func, bpf_iter_scx_dsq_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_scx_dsq_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur)
+BTF_ID_FLAGS(func, scx_bpf_cpuperf_set)
+BTF_ID_FLAGS(func, scx_bpf_nr_cpu_ids)
+BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask, KF_ACQUIRE)
+BTF_ID_FLAGS(func, scx_bpf_put_idle_cpumask, KF_RELEASE)
+BTF_ID_FLAGS(func, scx_bpf_test_and_clear_cpu_idle)
+BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
+BTF_ID_FLAGS(func, scx_bpf_cpu_rq)
+BTF_KFUNCS_END(scx_kfunc_ids_any)
+
+static const struct btf_kfunc_id_set scx_kfunc_set_any = {
+	.owner			= THIS_MODULE,
+	.set			= &scx_kfunc_ids_any,
+};
+
+static int __init scx_init(void)
+{
+	int ret;
+
+	/*
+	 * kfunc registration can't be done from init_sched_ext_class() as
+	 * register_btf_kfunc_id_set() needs most of the system to be up.
+	 *
+	 * Some kfuncs are context-sensitive and can only be called from
+	 * specific SCX ops. They are grouped into BTF sets accordingly.
+	 * Unfortunately, BPF currently doesn't have a way of enforcing such
+	 * restrictions. Eventually, the verifier should be able to enforce
+	 * them. For now, register them the same and make each kfunc explicitly
+	 * check using scx_kf_allowed().
+	 */
+	if ((ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					     &scx_kfunc_set_sleepable)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					     &scx_kfunc_set_select_cpu)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					     &scx_kfunc_set_enqueue_dispatch)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					     &scx_kfunc_set_dispatch)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					     &scx_kfunc_set_cpu_release)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
+					     &scx_kfunc_set_any)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
+					     &scx_kfunc_set_any)) ||
+	    (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL,
+					     &scx_kfunc_set_any))) {
+		pr_err("sched_ext: Failed to register kfunc sets (%d)\n", ret);
+		return ret;
+	}
+
+	ret = register_bpf_struct_ops(&bpf_sched_ext_ops, sched_ext_ops);
+	if (ret) {
+		pr_err("sched_ext: Failed to register struct_ops (%d)\n", ret);
+		return ret;
+	}
+
+	ret = register_pm_notifier(&scx_pm_notifier);
+	if (ret) {
+		pr_err("sched_ext: Failed to register PM notifier (%d)\n", ret);
+		return ret;
+	}
+
+	scx_kset = kset_create_and_add("sched_ext", &scx_uevent_ops, kernel_kobj);
+	if (!scx_kset) {
+		pr_err("sched_ext: Failed to create /sys/kernel/sched_ext\n");
+		return -ENOMEM;
+	}
+
+	ret = sysfs_create_group(&scx_kset->kobj, &scx_global_attr_group);
+	if (ret < 0) {
+		pr_err("sched_ext: Failed to add global attributes\n");
+		return ret;
+	}
+
+	return 0;
+}
+__initcall(scx_init);
diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h
new file mode 100644
index 000000000000..32d3a51f591a
--- /dev/null
+++ b/kernel/sched/ext.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#ifdef CONFIG_SCHED_CLASS_EXT
+
+void scx_tick(struct rq *rq);
+void init_scx_entity(struct sched_ext_entity *scx);
+void scx_pre_fork(struct task_struct *p);
+int scx_fork(struct task_struct *p);
+void scx_post_fork(struct task_struct *p);
+void scx_cancel_fork(struct task_struct *p);
+bool scx_can_stop_tick(struct rq *rq);
+void scx_rq_activate(struct rq *rq);
+void scx_rq_deactivate(struct rq *rq);
+int scx_check_setscheduler(struct task_struct *p, int policy);
+bool task_should_scx(struct task_struct *p);
+void init_sched_ext_class(void);
+
+static inline u32 scx_cpuperf_target(s32 cpu)
+{
+	if (scx_enabled())
+		return cpu_rq(cpu)->scx.cpuperf_target;
+	else
+		return 0;
+}
+
+static inline bool task_on_scx(const struct task_struct *p)
+{
+	return scx_enabled() && p->sched_class == &ext_sched_class;
+}
+
+#ifdef CONFIG_SCHED_CORE
+bool scx_prio_less(const struct task_struct *a, const struct task_struct *b,
+		   bool in_fi);
+#endif
+
+#else	/* CONFIG_SCHED_CLASS_EXT */
+
+static inline void scx_tick(struct rq *rq) {}
+static inline void scx_pre_fork(struct task_struct *p) {}
+static inline int scx_fork(struct task_struct *p) { return 0; }
+static inline void scx_post_fork(struct task_struct *p) {}
+static inline void scx_cancel_fork(struct task_struct *p) {}
+static inline u32 scx_cpuperf_target(s32 cpu) { return 0; }
+static inline bool scx_can_stop_tick(struct rq *rq) { return true; }
+static inline void scx_rq_activate(struct rq *rq) {}
+static inline void scx_rq_deactivate(struct rq *rq) {}
+static inline int scx_check_setscheduler(struct task_struct *p, int policy) { return 0; }
+static inline bool task_on_scx(const struct task_struct *p) { return false; }
+static inline void init_sched_ext_class(void) {}
+
+#endif	/* CONFIG_SCHED_CLASS_EXT */
+
+#if defined(CONFIG_SCHED_CLASS_EXT) && defined(CONFIG_SMP)
+void __scx_update_idle(struct rq *rq, bool idle);
+
+static inline void scx_update_idle(struct rq *rq, bool idle)
+{
+	if (scx_enabled())
+		__scx_update_idle(rq, idle);
+}
+#else
+static inline void scx_update_idle(struct rq *rq, bool idle) {}
+#endif
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 213c94d027a4..ee4fe81ba456 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4074,6 +4074,17 @@
 	load->inv_weight = sched_prio_to_wmult[prio];
 }
 
+static void reweight_task_fair(struct rq *rq, struct task_struct *p,
+			       const struct load_weight *lw)
+{
+	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+	struct load_weight *load = &se->load;
+
+	reweight_entity(cfs_rq, se, lw->weight);
+	load->inv_weight = lw->inv_weight;
+}
+
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -8348,7 +8348,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
 	 * Batch and idle tasks do not preempt non-idle tasks (their preemption
 	 * is driven by the tick):
 	 */
-	if (unlikely(p->policy != SCHED_NORMAL) || !sched_feat(WAKEUP_PREEMPTION))
+	if (unlikely(!normal_policy(p->policy)) || !sched_feat(WAKEUP_PREEMPTION))
 		return;
 
 	find_matching_se(&se, &pse);
@@ -9309,28 +9309,18 @@ static inline void update_blocked_load_status(struct rq *rq, bool has_blocked) {
 
 static bool __update_blocked_others(struct rq *rq, bool *done)
 {
-	const struct sched_class *curr_class;
-	u64 now = rq_clock_pelt(rq);
-	unsigned long thermal_pressure;
-	bool decayed;
+	bool updated;
 
 	/*
 	 * update_load_avg() can call cpufreq_update_util(). Make sure that RT,
 	 * DL and IRQ signals have been updated before updating CFS.
 	 */
-	curr_class = rq->curr->sched_class;
-
-	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
-
-	decayed = update_rt_rq_load_avg(now, rq, curr_class == &rt_sched_class) |
-		  update_dl_rq_load_avg(now, rq, curr_class == &dl_sched_class) |
-		  update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure) |
-		  update_irq_load_avg(rq, 0);
+	updated = update_other_load_avgs(rq);
 
 	if (others_have_blocked(rq))
 		*done = false;
 
-	return decayed;
+	return updated;
 }
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -13156,6 +13146,7 @@ DEFINE_SCHED_CLASS(fair) = {
 	.task_tick		= task_tick_fair,
 	.task_fork		= task_fork_fair,
 
+	.reweight_task		= reweight_task_fair,
 	.prio_changed		= prio_changed_fair,
 	.switched_from		= switched_from_fair,
 	.switched_to		= switched_to_fair,
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 6135fbe83d68..3b6540cc436a 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -458,11 +458,13 @@ static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags)
 
 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
 {
+	scx_update_idle(rq, false);
 }
 
 static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
 {
 	update_idle_core(rq);
+	scx_update_idle(rq, true);
 	schedstat_inc(rq->sched_goidle);
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ae50f212775e..9ce5074e8a8d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -173,9 +173,19 @@ static inline int idle_policy(int policy)
 {
 	return policy == SCHED_IDLE;
 }
+
+static inline int normal_policy(int policy)
+{
+#ifdef CONFIG_SCHED_CLASS_EXT
+	if (policy == SCHED_EXT)
+		return true;
+#endif
+	return policy == SCHED_NORMAL;
+}
+
 static inline int fair_policy(int policy)
 {
-	return policy == SCHED_NORMAL || policy == SCHED_BATCH;
+	return normal_policy(policy) || policy == SCHED_BATCH;
 }
 
 static inline int rt_policy(int policy)
@@ -223,6 +233,24 @@ static inline void update_avg(u64 *avg, u64 sample)
 #define shr_bound(val, shift)							\
 	(val >> min_t(typeof(shift), shift, BITS_PER_TYPE(typeof(val)) - 1))
 
+/*
+ * cgroup weight knobs should use the common MIN, DFL and MAX values which are
+ * 1, 100 and 10000 respectively. While it loses a bit of range on both ends, it
+ * maps pretty well onto the shares value used by scheduler and the round-trip
+ * conversions preserve the original value over the entire range.
+ */
+static inline unsigned long sched_weight_from_cgroup(unsigned long cgrp_weight)
+{
+	return DIV_ROUND_CLOSEST_ULL(cgrp_weight * 1024, CGROUP_WEIGHT_DFL);
+}
+
+static inline unsigned long sched_weight_to_cgroup(unsigned long weight)
+{
+	return clamp_t(unsigned long,
+		       DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024),
+		       CGROUP_WEIGHT_MIN, CGROUP_WEIGHT_MAX);
+}
+
 /*
  * !! For sched_setattr_nocheck() (kernel) only !!
  *
@@ -461,6 +489,11 @@ static inline int walk_tg_tree(tg_visitor down, tg_visitor up, void *data)
 	return walk_tg_tree_from(&root_task_group, down, up, data);
 }
 
+static inline struct task_group *css_tg(struct cgroup_subsys_state *css)
+{
+	return css ? container_of(css, struct task_group, css) : NULL;
+}
+
 extern int tg_nop(struct task_group *tg, void *data);
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -569,6 +602,12 @@ do {									\
 # define u64_u32_load(var)      u64_u32_load_copy(var, var##_copy)
 # define u64_u32_store(var, val) u64_u32_store_copy(var, var##_copy, val)
 
+struct rq;
+struct balance_callback {
+	struct balance_callback *next;
+	void (*func)(struct rq *rq);
+};
+
 /* CFS-related fields in a runqueue */
 struct cfs_rq {
 	struct load_weight	load;
@@ -677,6 +716,42 @@ struct cfs_rq {
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 };
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+/* scx_rq->flags, protected by the rq lock */
+enum scx_rq_flags {
+	/*
+	 * A hotplugged CPU starts scheduling before rq_online_scx(). Track
+	 * ops.cpu_on/offline() state so that ops.enqueue/dispatch() are called
+	 * only while the BPF scheduler considers the CPU to be online.
+	 */
+	SCX_RQ_ONLINE		= 1 << 0,
+	SCX_RQ_CAN_STOP_TICK	= 1 << 1,
+
+	SCX_RQ_IN_WAKEUP	= 1 << 16,
+	SCX_RQ_IN_BALANCE	= 1 << 17,
+};
+
+struct scx_rq {
+	struct scx_dispatch_q	local_dsq;
+	struct list_head	runnable_list;		/* runnable tasks on this rq */
+	struct list_head	ddsp_deferred_locals;	/* deferred ddsps from enq */
+	unsigned long		ops_qseq;
+	u64			extra_enq_flags;	/* see move_task_to_local_dsq() */
+	u32			nr_running;
+	u32			flags;
+	u32			cpuperf_target;		/* [0, SCHED_CAPACITY_SCALE] */
+	bool			cpu_released;
+	cpumask_var_t		cpus_to_kick;
+	cpumask_var_t		cpus_to_kick_if_idle;
+	cpumask_var_t		cpus_to_preempt;
+	cpumask_var_t		cpus_to_wait;
+	unsigned long		pnt_seq;
+	struct balance_callback	deferred_bal_cb;
+	struct irq_work		deferred_irq_work;
+	struct irq_work		kick_cpus_irq_work;
+};
+#endif /* CONFIG_SCHED_CLASS_EXT */
+
 static inline int rt_bandwidth_enabled(void)
 {
 	return sysctl_sched_rt_runtime >= 0;
@@ -969,12 +1044,6 @@ struct uclamp_rq {
 DECLARE_STATIC_KEY_FALSE(sched_uclamp_used);
 #endif /* CONFIG_UCLAMP_TASK */
 
-struct rq;
-struct balance_callback {
-	struct balance_callback *next;
-	void (*func)(struct rq *rq);
-};
-
 /*
  * This is the main, per-CPU runqueue data structure.
  *
@@ -1017,6 +1086,9 @@ struct rq {
 	struct cfs_rq		cfs;
 	struct rt_rq		rt;
 	struct dl_rq		dl;
+#ifdef CONFIG_SCHED_CLASS_EXT
+	struct scx_rq		scx;
+#endif
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	/* list of leaf cfs_rq on this CPU: */
@@ -2276,6 +2348,8 @@ struct sched_class {
 	void (*put_prev_task)(struct rq *rq, struct task_struct *p);
 	void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first);
 
+	void (*switch_class)(struct rq *rq, struct task_struct *next);
+
 #ifdef CONFIG_SMP
 	int (*balance)(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
 	int  (*select_task_rq)(struct task_struct *p, int task_cpu, int flags);
@@ -2303,8 +2377,11 @@ struct sched_class {
 	 * cannot assume the switched_from/switched_to pair is serialized by
 	 * rq->lock. They are however serialized by p->pi_lock.
 	 */
+	void (*switching_to) (struct rq *this_rq, struct task_struct *task);
 	void (*switched_from)(struct rq *this_rq, struct task_struct *task);
 	void (*switched_to)  (struct rq *this_rq, struct task_struct *task);
+	void (*reweight_task)(struct rq *this_rq, struct task_struct *task,
+			      const struct load_weight *lw);
 	void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
 			      int oldprio);
 
@@ -2353,19 +2430,54 @@ const struct sched_class name##_sched_class \
 extern struct sched_class __sched_class_highest[];
 extern struct sched_class __sched_class_lowest[];
 
+extern const struct sched_class stop_sched_class;
+extern const struct sched_class dl_sched_class;
+extern const struct sched_class rt_sched_class;
+extern const struct sched_class fair_sched_class;
+extern const struct sched_class idle_sched_class;
+
+#ifdef CONFIG_SCHED_CLASS_EXT
+extern const struct sched_class ext_sched_class;
+
+DECLARE_STATIC_KEY_FALSE(__scx_ops_enabled);	/* SCX BPF scheduler loaded */
+DECLARE_STATIC_KEY_FALSE(__scx_switched_all);	/* all fair class tasks on SCX */
+
+#define scx_enabled()		static_branch_unlikely(&__scx_ops_enabled)
+#define scx_switched_all()	static_branch_unlikely(&__scx_switched_all)
+#else /* !CONFIG_SCHED_CLASS_EXT */
+#define scx_enabled()		false
+#define scx_switched_all()	false
+#endif /* !CONFIG_SCHED_CLASS_EXT */
+
+/*
+ * Iterate only active classes. SCX can take over all fair tasks or be
+ * completely disabled. If the former, skip fair. If the latter, skip SCX.
+ */
+static inline const struct sched_class *next_active_class(const struct sched_class *class)
+{
+	class++;
+#ifdef CONFIG_SCHED_CLASS_EXT
+	if (scx_switched_all() && class == &fair_sched_class)
+		class++;
+	if (!scx_enabled() && class == &ext_sched_class)
+		class++;
+#endif
+	return class;
+}
+
 #define for_class_range(class, _from, _to) \
 	for (class = (_from); class < (_to); class++)
 
 #define for_each_class(class) \
 	for_class_range(class, __sched_class_highest, __sched_class_lowest)
 
-#define sched_class_above(_a, _b)	((_a) < (_b))
+#define for_active_class_range(class, _from, _to)				\
+	for (class = (_from); class != (_to); class = next_active_class(class))
 
-extern const struct sched_class stop_sched_class;
-extern const struct sched_class dl_sched_class;
-extern const struct sched_class rt_sched_class;
-extern const struct sched_class fair_sched_class;
-extern const struct sched_class idle_sched_class;
+#define for_each_active_class(class)						\
+	for_active_class_range(class, __sched_class_highest, __sched_class_lowest)
+
+#define sched_class_above(_a, _b)	((_a) < (_b))
 
 static inline bool sched_stop_runnable(struct rq *rq)
 {
@@ -2462,7 +2574,7 @@ extern void init_sched_dl_class(void);
 extern void init_sched_rt_class(void);
 extern void init_sched_fair_class(void);
 
-extern void reweight_task(struct task_struct *p, int prio);
+extern void __setscheduler_prio(struct task_struct *p, int prio);
 
 extern void resched_curr(struct rq *rq);
 extern void resched_cpu(int cpu);
@@ -2542,6 +2654,12 @@ static inline void sub_nr_running(struct rq *rq, unsigned count)
 extern void activate_task(struct rq *rq, struct task_struct *p, int flags);
 extern void deactivate_task(struct rq *rq, struct task_struct *p, int flags);
 
+extern void check_class_changing(struct rq *rq, struct task_struct *p,
+				 const struct sched_class *prev_class);
+extern void check_class_changed(struct rq *rq, struct task_struct *p,
+				const struct sched_class *prev_class,
+				int oldprio);
+
 extern void wakeup_preempt(struct rq *rq, struct task_struct *p, int flags);
 
 #ifdef CONFIG_PREEMPT_RT
@@ -3007,6 +3125,9 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
 #endif
 
 #ifdef CONFIG_SMP
+
+bool update_other_load_avgs(struct rq *rq);
+
 unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
 				 unsigned long *min,
 				 unsigned long *max);
@@ -3049,6 +3170,8 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
 {
 	return READ_ONCE(rq->avg_rt.util_avg);
 }
+#else /* !CONFIG_SMP */
+static inline bool update_other_load_avgs(struct rq *rq) { return false; }
 #endif
 
 #ifdef CONFIG_UCLAMP_TASK
@@ -3481,4 +3604,24 @@ static inline void init_sched_mm_cid(struct task_struct *t) { }
 extern u64 avg_vruntime(struct cfs_rq *cfs_rq);
 extern int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se);
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+/*
+ * Used by SCX in the enable/disable paths to move tasks between sched_classes
+ * and establish invariants.
+ */
+struct sched_enq_and_set_ctx {
+	struct task_struct	*p;
+	int			queue_flags;
+	bool			queued;
+	bool			running;
+};
+
+void sched_deq_and_put_task(struct task_struct *p, int queue_flags,
+			    struct sched_enq_and_set_ctx *ctx);
+void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx);
+
+#endif /* CONFIG_SCHED_CLASS_EXT */
+
+#include "ext.h"
+
 #endif /* _KERNEL_SCHED_SCHED_H */
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 222c6d6c8281..9581ef4efec5 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -68,6 +68,7 @@ void dump_stack_print_info(const char *log_lvl)
 
 	print_worker_info(log_lvl, current);
 	print_stop_info(log_lvl, current);
+	print_scx_info(log_lvl, current);
 }
 
 /**
diff --git a/tools/Makefile b/tools/Makefile
index 276f5d0d53a4..278d24723b74 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -28,6 +28,7 @@ help:
 	@echo '  pci                    - PCI tools'
 	@echo '  perf                   - Linux performance measurement and analysis tool'
 	@echo '  selftests              - various kernel selftests'
+	@echo '  sched_ext              - sched_ext example schedulers'
 	@echo '  bootconfig             - boot config tool'
 	@echo '  spi                    - spi tools'
 	@echo '  tmon                   - thermal monitoring and tuning tool'
@@ -91,6 +92,9 @@ perf: FORCE
 	$(Q)mkdir -p $(PERF_O) .
 	$(Q)$(MAKE) --no-print-directory -C perf O=$(PERF_O) subdir=
 
+sched_ext: FORCE
+	$(call descend,sched_ext)
+
 selftests: FORCE
 	$(call descend,testing/$@)
 
@@ -184,6 +188,9 @@ perf_clean:
 	$(Q)mkdir -p $(PERF_O) .
 	$(Q)$(MAKE) --no-print-directory -C perf O=$(PERF_O) subdir= clean
 
+sched_ext_clean:
+	$(call descend,sched_ext,clean)
+
 selftests_clean:
 	$(call descend,testing/$(@:_clean=),clean)
 
@@ -213,6 +220,7 @@ clean: acpi_clean counter_clean cpupower_clean hv_clean firewire_clean \
 		mm_clean bpf_clean iio_clean x86_energy_perf_policy_clean tmon_clean \
 		freefall_clean build_clean libbpf_clean libsubcmd_clean \
 		gpio_clean objtool_clean leds_clean wmi_clean pci_clean firmware_clean debugging_clean \
-		intel-speed-select_clean tracing_clean thermal_clean thermometer_clean thermal-engine_clean
+		intel-speed-select_clean tracing_clean thermal_clean thermometer_clean thermal-engine_clean \
+		sched_ext_clean
 
 .PHONY: FORCE
diff --git a/tools/sched_ext/.gitignore b/tools/sched_ext/.gitignore
new file mode 100644
index 000000000000..d6264fe1c8cd
--- /dev/null
+++ b/tools/sched_ext/.gitignore
@@ -0,0 +1,2 @@
+tools/
+build/
diff --git a/tools/sched_ext/Makefile b/tools/sched_ext/Makefile
new file mode 100644
index 000000000000..bf7e108f5ae1
--- /dev/null
+++ b/tools/sched_ext/Makefile
@@ -0,0 +1,246 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+include ../build/Build.include
+include ../scripts/Makefile.arch
+include ../scripts/Makefile.include
+
+all: all_targets
+
+ifneq ($(LLVM),)
+ifneq ($(filter %/,$(LLVM)),)
+LLVM_PREFIX := $(LLVM)
+else ifneq ($(filter -%,$(LLVM)),)
+LLVM_SUFFIX := $(LLVM)
+endif
+
+CLANG_TARGET_FLAGS_arm          := arm-linux-gnueabi
+CLANG_TARGET_FLAGS_arm64        := aarch64-linux-gnu
+CLANG_TARGET_FLAGS_hexagon      := hexagon-linux-musl
+CLANG_TARGET_FLAGS_m68k         := m68k-linux-gnu
+CLANG_TARGET_FLAGS_mips         := mipsel-linux-gnu
+CLANG_TARGET_FLAGS_powerpc      := powerpc64le-linux-gnu
+CLANG_TARGET_FLAGS_riscv        := riscv64-linux-gnu
+CLANG_TARGET_FLAGS_s390         := s390x-linux-gnu
+CLANG_TARGET_FLAGS_x86          := x86_64-linux-gnu
+CLANG_TARGET_FLAGS              := $(CLANG_TARGET_FLAGS_$(ARCH))
+
+ifeq ($(CROSS_COMPILE),)
+ifeq ($(CLANG_TARGET_FLAGS),)
+$(error Specify CROSS_COMPILE or add '--target=' option to lib.mk)
+else
+CLANG_FLAGS     += --target=$(CLANG_TARGET_FLAGS)
+endif # CLANG_TARGET_FLAGS
+else
+CLANG_FLAGS     += --target=$(notdir $(CROSS_COMPILE:%-=%))
+endif # CROSS_COMPILE
+
+CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as
+else
+CC := $(CROSS_COMPILE)gcc
+endif # LLVM
+
+CURDIR := $(abspath .)
+TOOLSDIR := $(abspath ..)
+LIBDIR := $(TOOLSDIR)/lib
+BPFDIR := $(LIBDIR)/bpf
+TOOLSINCDIR := $(TOOLSDIR)/include
+BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
+APIDIR := $(TOOLSINCDIR)/uapi
+GENDIR := $(abspath ../../include/generated)
+GENHDR := $(GENDIR)/autoconf.h
+
+ifeq ($(O),)
+OUTPUT_DIR := $(CURDIR)/build
+else
+OUTPUT_DIR := $(O)/build
+endif # O
+OBJ_DIR := $(OUTPUT_DIR)/obj
+INCLUDE_DIR := $(OUTPUT_DIR)/include
+BPFOBJ_DIR := $(OBJ_DIR)/libbpf
+SCXOBJ_DIR := $(OBJ_DIR)/sched_ext
+BINDIR := $(OUTPUT_DIR)/bin
+BPFOBJ := $(BPFOBJ_DIR)/libbpf.a
+ifneq ($(CROSS_COMPILE),)
+HOST_BUILD_DIR		:= $(OBJ_DIR)/host
+HOST_OUTPUT_DIR	:= host-tools
+HOST_INCLUDE_DIR	:= $(HOST_OUTPUT_DIR)/include
+else
+HOST_BUILD_DIR		:= $(OBJ_DIR)
+HOST_OUTPUT_DIR	:= $(OUTPUT_DIR)
+HOST_INCLUDE_DIR	:= $(INCLUDE_DIR)
+endif
+HOST_BPFOBJ := $(HOST_BUILD_DIR)/libbpf/libbpf.a
+RESOLVE_BTFIDS := $(HOST_BUILD_DIR)/resolve_btfids/resolve_btfids
+DEFAULT_BPFTOOL := $(HOST_OUTPUT_DIR)/sbin/bpftool
+
+VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)					\
+		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)		\
+		     ../../vmlinux						\
+		     /sys/kernel/btf/vmlinux					\
+		     /boot/vmlinux-$(shell uname -r)
+VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
+ifeq ($(VMLINUX_BTF),)
+$(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
+endif
+
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+
+ifneq ($(wildcard $(GENHDR)),)
+  GENFLAGS := -DHAVE_GENHDR
+endif
+
+CFLAGS += -g -O2 -rdynamic -pthread -Wall -Werror $(GENFLAGS)			\
+	  -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)				\
+	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(CURDIR)/include
+
+# Silence some warnings when compiled with clang
+ifneq ($(LLVM),)
+CFLAGS += -Wno-unused-command-line-argument
+endif
+
+LDFLAGS = -lelf -lz -lpthread
+
+IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null |				\
+			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
+
+# Get Clang's default includes on this system, as opposed to those seen by
+# '-target bpf'. This fixes "missing" files on some architectures/distros,
+# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
+#
+# Use '-idirafter': Don't interfere with include mechanics except where the
+# build would have failed anyways.
+define get_sys_includes
+$(shell $(1) -v -E - </dev/null 2>&1 \
+	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
+$(shell $(1) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
+endef
+
+BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH)					\
+	     $(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)		\
+	     -I$(CURDIR)/include -I$(CURDIR)/include/bpf-compat			\
+	     -I$(INCLUDE_DIR) -I$(APIDIR)					\
+	     -I../../include							\
+	     $(call get_sys_includes,$(CLANG))					\
+	     -Wall -Wno-compare-distinct-pointer-types				\
+	     -O2 -mcpu=v3
+
+# sort removes libbpf duplicates when not cross-building
+MAKE_DIRS := $(sort $(OBJ_DIR)/libbpf $(HOST_BUILD_DIR)/libbpf			\
+	       $(HOST_BUILD_DIR)/bpftool $(HOST_BUILD_DIR)/resolve_btfids	\
+	       $(INCLUDE_DIR) $(SCXOBJ_DIR) $(BINDIR))
+
+$(MAKE_DIRS):
+	$(call msg,MKDIR,,$@)
+	$(Q)mkdir -p $@
+
+$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)			\
+	   $(APIDIR)/linux/bpf.h						\
+	   | $(OBJ_DIR)/libbpf
+	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(OBJ_DIR)/libbpf/	\
+		    EXTRA_CFLAGS='-g -O0 -fPIC'					\
+		    DESTDIR=$(OUTPUT_DIR) prefix= all install_headers
+
+$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)	\
+		    $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
+	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)				\
+		    ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD)		\
+		    EXTRA_CFLAGS='-g -O0'					\
+		    OUTPUT=$(HOST_BUILD_DIR)/bpftool/				\
+		    LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/			\
+		    LIBBPF_DESTDIR=$(HOST_OUTPUT_DIR)/				\
+		    prefix= DESTDIR=$(HOST_OUTPUT_DIR)/ install-bin
+
+$(INCLUDE_DIR)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR)
+ifeq ($(VMLINUX_H),)
+	$(call msg,GEN,,$@)
+	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@
+else
+	$(call msg,CP,,$@)
+	$(Q)cp "$(VMLINUX_H)" $@
+endif
+
+$(SCXOBJ_DIR)/%.bpf.o: %.bpf.c $(INCLUDE_DIR)/vmlinux.h include/scx/*.h		\
+		       | $(BPFOBJ) $(SCXOBJ_DIR)
+	$(call msg,CLNG-BPF,,$(notdir $@))
+	$(Q)$(CLANG) $(BPF_CFLAGS) -target bpf -c $< -o $@
+
+$(INCLUDE_DIR)/%.bpf.skel.h: $(SCXOBJ_DIR)/%.bpf.o $(INCLUDE_DIR)/vmlinux.h $(BPFTOOL)
+	$(eval sched=$(notdir $@))
+	$(call msg,GEN-SKEL,,$(sched))
+	$(Q)$(BPFTOOL) gen object $(<:.o=.linked1.o) $<
+	$(Q)$(BPFTOOL) gen object $(<:.o=.linked2.o) $(<:.o=.linked1.o)
+	$(Q)$(BPFTOOL) gen object $(<:.o=.linked3.o) $(<:.o=.linked2.o)
+	$(Q)diff $(<:.o=.linked2.o) $(<:.o=.linked3.o)
+	$(Q)$(BPFTOOL) gen skeleton $(<:.o=.linked3.o) name $(subst .bpf.skel.h,,$(sched)) > $@
+	$(Q)$(BPFTOOL) gen subskeleton $(<:.o=.linked3.o) name $(subst .bpf.skel.h,,$(sched)) > $(@:.skel.h=.subskel.h)
+
+SCX_COMMON_DEPS := include/scx/common.h include/scx/user_exit_info.h | $(BINDIR)
+
+c-sched-targets = scx_simple scx_qmap scx_central
+
+$(addprefix $(BINDIR)/,$(c-sched-targets)): \
+	$(BINDIR)/%: \
+		$(filter-out %.bpf.c,%.c) \
+		$(INCLUDE_DIR)/%.bpf.skel.h \
+		$(SCX_COMMON_DEPS)
+	$(eval sched=$(notdir $@))
+	$(CC) $(CFLAGS) -c $(sched).c -o $(SCXOBJ_DIR)/$(sched).o
+	$(CC) -o $@ $(SCXOBJ_DIR)/$(sched).o $(HOST_BPFOBJ) $(LDFLAGS)
+
+$(c-sched-targets): %: $(BINDIR)/%
+
+install: all
+	$(Q)mkdir -p $(DESTDIR)/usr/local/bin/
+	$(Q)cp $(BINDIR)/* $(DESTDIR)/usr/local/bin/
+
+clean:
+	rm -rf $(OUTPUT_DIR) $(HOST_OUTPUT_DIR)
+	rm -f *.o *.bpf.o *.bpf.skel.h *.bpf.subskel.h
+	rm -f $(c-sched-targets)
+
+help:
+	@echo   'Building targets'
+	@echo   '================'
+	@echo   ''
+	@echo   '  all		  - Compile all schedulers'
+	@echo   ''
+	@echo   'Alternatively, you may compile individual schedulers:'
+	@echo   ''
+	@printf '  %s\n' $(c-sched-targets)
+	@echo   ''
+	@echo   'For any scheduler build target, you may specify an alternative'
+	@echo   'build output path with the O= environment variable. For example:'
+	@echo   ''
+	@echo   '   O=/tmp/sched_ext make all'
+	@echo   ''
+	@echo   'will compile all schedulers, and emit the build artifacts to'
+	@echo   '/tmp/sched_ext/build.'
+	@echo   ''
+	@echo   ''
+	@echo   'Installing targets'
+	@echo   '=================='
+	@echo   ''
+	@echo   '  install	  - Compile and install all schedulers to /usr/bin.'
+	@echo   '		    You may specify the DESTDIR= environment variable'
+	@echo   '		    to indicate a prefix for /usr/bin. For example:'
+	@echo   ''
+	@echo   '                     DESTDIR=/tmp/sched_ext make install'
+	@echo   ''
+	@echo   '		    will build the schedulers in CWD/build, and'
+	@echo   '		    install the schedulers to /tmp/sched_ext/usr/bin.'
+	@echo   ''
+	@echo   ''
+	@echo   'Cleaning targets'
+	@echo   '================'
+	@echo   ''
+	@echo   '  clean		  - Remove all generated files'
+
+all_targets: $(c-sched-targets)
+
+.PHONY: all all_targets $(c-sched-targets) clean help
+
+# delete failed targets
+.DELETE_ON_ERROR:
+
+# keep intermediate (.bpf.skel.h, .bpf.o, etc) targets
+.SECONDARY:
diff --git a/tools/sched_ext/README.md b/tools/sched_ext/README.md
new file mode 100644
index 000000000000..8efe70cc4363
--- /dev/null
+++ b/tools/sched_ext/README.md
@@ -0,0 +1,258 @@
+SCHED_EXT EXAMPLE SCHEDULERS
+============================
+
+# Introduction
+
+This directory contains a number of example sched_ext schedulers. These
+schedulers are meant to provide examples of different types of schedulers
+that can be built using sched_ext, and illustrate how various features of
+sched_ext can be used.
+
+Some of the examples are performant, production-ready schedulers. That is, for
+the correct workload and with the correct tuning, they may be deployed in a
+production environment with acceptable or possibly even improved performance.
+Others are just examples that in practice, would not provide acceptable
+performance (though they could be improved to get there).
+
+This README will describe these example schedulers, including describing the
+types of workloads or scenarios they're designed to accommodate, and whether or
+not they're production ready. For more details on any of these schedulers,
+please see the header comment in their .bpf.c file.
+
+
+# Compiling the examples
+
+There are a few toolchain dependencies for compiling the example schedulers.
+
+## Toolchain dependencies
+
+1. clang >= 16.0.0
+
+The schedulers are BPF programs, and therefore must be compiled with clang. gcc
+is actively working on adding a BPF backend compiler as well, but are still
+missing some features such as BTF type tags which are necessary for using
+kptrs.
+
+2. pahole >= 1.25
+
+You may need pahole in order to generate BTF from DWARF.
+
+3. rust >= 1.70.0
+
+Rust schedulers uses features present in the rust toolchain >= 1.70.0. You
+should be able to use the stable build from rustup, but if that doesn't
+work, try using the rustup nightly build.
+
+There are other requirements as well, such as make, but these are the main /
+non-trivial ones.
+
+## Compiling the kernel
+
+In order to run a sched_ext scheduler, you'll have to run a kernel compiled
+with the patches in this repository, and with a minimum set of necessary
+Kconfig options:
+
+```
+CONFIG_BPF=y
+CONFIG_SCHED_CLASS_EXT=y
+CONFIG_BPF_SYSCALL=y
+CONFIG_BPF_JIT=y
+CONFIG_DEBUG_INFO_BTF=y
+```
+
+It's also recommended that you also include the following Kconfig options:
+
+```
+CONFIG_BPF_JIT_ALWAYS_ON=y
+CONFIG_BPF_JIT_DEFAULT_ON=y
+CONFIG_PAHOLE_HAS_SPLIT_BTF=y
+CONFIG_PAHOLE_HAS_BTF_TAG=y
+```
+
+There is a `Kconfig` file in this directory whose contents you can append to
+your local `.config` file, as long as there are no conflicts with any existing
+options in the file.
+
+## Getting a vmlinux.h file
+
+You may notice that most of the example schedulers include a "vmlinux.h" file.
+This is a large, auto-generated header file that contains all of the types
+defined in some vmlinux binary that was compiled with
+[BTF](https://docs.kernel.org/bpf/btf.html) (i.e. with the BTF-related Kconfig
+options specified above).
+
+The header file is created using `bpftool`, by passing it a vmlinux binary
+compiled with BTF as follows:
+
+```bash
+$ bpftool btf dump file /path/to/vmlinux format c > vmlinux.h
+```
+
+`bpftool` analyzes all of the BTF encodings in the binary, and produces a
+header file that can be included by BPF programs to access those types.  For
+example, using vmlinux.h allows a scheduler to access fields defined directly
+in vmlinux as follows:
+
+```c
+#include "vmlinux.h"
+// vmlinux.h is also implicitly included by scx_common.bpf.h.
+#include "scx_common.bpf.h"
+
+/*
+ * vmlinux.h provides definitions for struct task_struct and
+ * struct scx_enable_args.
+ */
+void BPF_STRUCT_OPS(example_enable, struct task_struct *p,
+		    struct scx_enable_args *args)
+{
+	bpf_printk("Task %s enabled in example scheduler", p->comm);
+}
+
+// vmlinux.h provides the definition for struct sched_ext_ops.
+SEC(".struct_ops.link")
+struct sched_ext_ops example_ops {
+	.enable	= (void *)example_enable,
+	.name	= "example",
+}
+```
+
+The scheduler build system will generate this vmlinux.h file as part of the
+scheduler build pipeline. It looks for a vmlinux file in the following
+dependency order:
+
+1. If the O= environment variable is defined, at `$O/vmlinux`
+2. If the KBUILD_OUTPUT= environment variable is defined, at
+   `$KBUILD_OUTPUT/vmlinux`
+3. At `../../vmlinux` (i.e. at the root of the kernel tree where you're
+   compiling the schedulers)
+3. `/sys/kernel/btf/vmlinux`
+4. `/boot/vmlinux-$(uname -r)`
+
+In other words, if you have compiled a kernel in your local repo, its vmlinux
+file will be used to generate vmlinux.h. Otherwise, it will be the vmlinux of
+the kernel you're currently running on. This means that if you're running on a
+kernel with sched_ext support, you may not need to compile a local kernel at
+all.
+
+### Aside on CO-RE
+
+One of the cooler features of BPF is that it supports
+[CO-RE](https://nakryiko.com/posts/bpf-core-reference-guide/) (Compile Once Run
+Everywhere). This feature allows you to reference fields inside of structs with
+types defined internal to the kernel, and not have to recompile if you load the
+BPF program on a different kernel with the field at a different offset. In our
+example above, we print out a task name with `p->comm`. CO-RE would perform
+relocations for that access when the program is loaded to ensure that it's
+referencing the correct offset for the currently running kernel.
+
+## Compiling the schedulers
+
+Once you have your toolchain setup, and a vmlinux that can be used to generate
+a full vmlinux.h file, you can compile the schedulers using `make`:
+
+```bash
+$ make -j($nproc)
+```
+
+# Example schedulers
+
+This directory contains the following example schedulers. These schedulers are
+for testing and demonstrating different aspects of sched_ext. While some may be
+useful in limited scenarios, they are not intended to be practical.
+
+For more scheduler implementations, tools and documentation, visit
+https://github.com/sched-ext/scx.
+
+## scx_simple
+
+A simple scheduler that provides an example of a minimal sched_ext scheduler.
+scx_simple can be run in either global weighted vtime mode, or FIFO mode.
+
+Though very simple, in limited scenarios, this scheduler can perform reasonably
+well on single-socket systems with a unified L3 cache.
+
+## scx_qmap
+
+Another simple, yet slightly more complex scheduler that provides an example of
+a basic weighted FIFO queuing policy. It also provides examples of some common
+useful BPF features, such as sleepable per-task storage allocation in the
+`ops.prep_enable()` callback, and using the `BPF_MAP_TYPE_QUEUE` map type to
+enqueue tasks. It also illustrates how core-sched support could be implemented.
+
+## scx_central
+
+A "central" scheduler where scheduling decisions are made from a single CPU.
+This scheduler illustrates how scheduling decisions can be dispatched from a
+single CPU, allowing other cores to run with infinite slices, without timer
+ticks, and without having to incur the overhead of making scheduling decisions.
+
+The approach demonstrated by this scheduler may be useful for any workload that
+benefits from minimizing scheduling overhead and timer ticks. An example of
+where this could be particularly useful is running VMs, where running with
+infinite slices and no timer ticks allows the VM to avoid unnecessary expensive
+vmexits.
+
+
+# Troubleshooting
+
+There are a number of common issues that you may run into when building the
+schedulers. We'll go over some of the common ones here.
+
+## Build Failures
+
+### Old version of clang
+
+```
+error: static assertion failed due to requirement 'SCX_DSQ_FLAG_BUILTIN': bpftool generated vmlinux.h is missing high bits for 64bit enums, upgrade clang and pahole
+        _Static_assert(SCX_DSQ_FLAG_BUILTIN,
+                       ^~~~~~~~~~~~~~~~~~~~
+1 error generated.
+```
+
+This means you built the kernel or the schedulers with an older version of
+clang than what's supported (i.e. older than 16.0.0). To remediate this:
+
+1. `which clang` to make sure you're using a sufficiently new version of clang.
+
+2. `make fullclean` in the root path of the repository, and rebuild the kernel
+   and schedulers.
+
+3. Rebuild the kernel, and then your example schedulers.
+
+The schedulers are also cleaned if you invoke `make mrproper` in the root
+directory of the tree.
+
+### Stale kernel build / incomplete vmlinux.h file
+
+As described above, you'll need a `vmlinux.h` file that was generated from a
+vmlinux built with BTF, and with sched_ext support enabled. If you don't,
+you'll see errors such as the following which indicate that a type being
+referenced in a scheduler is unknown:
+
+```
+/path/to/sched_ext/tools/sched_ext/user_exit_info.h:25:23: note: forward declaration of 'struct scx_exit_info'
+
+const struct scx_exit_info *ei)
+
+^
+```
+
+In order to resolve this, please follow the steps above in
+[Getting a vmlinux.h file](#getting-a-vmlinuxh-file) in order to ensure your
+schedulers are using a vmlinux.h file that includes the requisite types.
+
+## Misc
+
+### llvm: [OFF]
+
+You may see the following output when building the schedulers:
+
+```
+Auto-detecting system features:
+...                         clang-bpf-co-re: [ on  ]
+...                                    llvm: [ OFF ]
+...                                  libcap: [ on  ]
+...                                  libbfd: [ on  ]
+```
+
+Seeing `llvm: [ OFF ]` here is not an issue. You can safely ignore.
diff --git a/tools/sched_ext/include/bpf-compat/gnu/stubs.h b/tools/sched_ext/include/bpf-compat/gnu/stubs.h
new file mode 100644
index 000000000000..ad7d139ce907
--- /dev/null
+++ b/tools/sched_ext/include/bpf-compat/gnu/stubs.h
@@ -0,0 +1,11 @@
+/*
+ * Dummy gnu/stubs.h. clang can end up including /usr/include/gnu/stubs.h when
+ * compiling BPF files although its content doesn't play any role. The file in
+ * turn includes stubs-64.h or stubs-32.h depending on whether __x86_64__ is
+ * defined. When compiling a BPF source, __x86_64__ isn't set and thus
+ * stubs-32.h is selected. However, the file is not there if the system doesn't
+ * have 32bit glibc devel package installed leading to a build failure.
+ *
+ * The problem is worked around by making this file available in the include
+ * search paths before the system one when building BPF.
+ */
diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
new file mode 100644
index 000000000000..20280df62857
--- /dev/null
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -0,0 +1,401 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#ifndef __SCX_COMMON_BPF_H
+#define __SCX_COMMON_BPF_H
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include <asm-generic/errno.h>
+#include "user_exit_info.h"
+
+#define PF_WQ_WORKER			0x00000020	/* I'm a workqueue worker */
+#define PF_KTHREAD			0x00200000	/* I am a kernel thread */
+#define PF_EXITING			0x00000004
+#define CLOCK_MONOTONIC			1
+
+/*
+ * Earlier versions of clang/pahole lost upper 32bits in 64bit enums which can
+ * lead to really confusing misbehaviors. Let's trigger a build failure.
+ */
+static inline void ___vmlinux_h_sanity_check___(void)
+{
+	_Static_assert(SCX_DSQ_FLAG_BUILTIN,
+		       "bpftool generated vmlinux.h is missing high bits for 64bit enums, upgrade clang and pahole");
+}
+
+s32 scx_bpf_create_dsq(u64 dsq_id, s32 node) __ksym;
+s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool *is_idle) __ksym;
+void scx_bpf_dispatch(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym;
+void scx_bpf_dispatch_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym;
+u32 scx_bpf_dispatch_nr_slots(void) __ksym;
+void scx_bpf_dispatch_cancel(void) __ksym;
+bool scx_bpf_consume(u64 dsq_id) __ksym;
+u32 scx_bpf_reenqueue_local(void) __ksym;
+void scx_bpf_kick_cpu(s32 cpu, u64 flags) __ksym;
+s32 scx_bpf_dsq_nr_queued(u64 dsq_id) __ksym;
+void scx_bpf_destroy_dsq(u64 dsq_id) __ksym;
+int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id, u64 flags) __ksym __weak;
+struct task_struct *bpf_iter_scx_dsq_next(struct bpf_iter_scx_dsq *it) __ksym __weak;
+void bpf_iter_scx_dsq_destroy(struct bpf_iter_scx_dsq *it) __ksym __weak;
+void scx_bpf_exit_bstr(s64 exit_code, char *fmt, unsigned long long *data, u32 data__sz) __ksym __weak;
+void scx_bpf_error_bstr(char *fmt, unsigned long long *data, u32 data_len) __ksym;
+void scx_bpf_dump_bstr(char *fmt, unsigned long long *data, u32 data_len) __ksym __weak;
+u32 scx_bpf_cpuperf_cap(s32 cpu) __ksym __weak;
+u32 scx_bpf_cpuperf_cur(s32 cpu) __ksym __weak;
+void scx_bpf_cpuperf_set(s32 cpu, u32 perf) __ksym __weak;
+u32 scx_bpf_nr_cpu_ids(void) __ksym __weak;
+const struct cpumask *scx_bpf_get_possible_cpumask(void) __ksym __weak;
+const struct cpumask *scx_bpf_get_online_cpumask(void) __ksym __weak;
+void scx_bpf_put_cpumask(const struct cpumask *cpumask) __ksym __weak;
+const struct cpumask *scx_bpf_get_idle_cpumask(void) __ksym;
+const struct cpumask *scx_bpf_get_idle_smtmask(void) __ksym;
+void scx_bpf_put_idle_cpumask(const struct cpumask *cpumask) __ksym;
+bool scx_bpf_test_and_clear_cpu_idle(s32 cpu) __ksym;
+s32 scx_bpf_pick_idle_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
+s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
+bool scx_bpf_task_running(const struct task_struct *p) __ksym;
+s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym;
+struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym;
+
+static inline __attribute__((format(printf, 1, 2)))
+void ___scx_bpf_bstr_format_checker(const char *fmt, ...) {}
+
+/*
+ * Helper macro for initializing the fmt and variadic argument inputs to both
+ * bstr exit kfuncs. Callers to this function should use ___fmt and ___param to
+ * refer to the initialized list of inputs to the bstr kfunc.
+ */
+#define scx_bpf_bstr_preamble(fmt, args...)					\
+	static char ___fmt[] = fmt;						\
+	/*									\
+	 * Note that __param[] must have at least one				\
+	 * element to keep the verifier happy.					\
+	 */									\
+	unsigned long long ___param[___bpf_narg(args) ?: 1] = {};		\
+										\
+	_Pragma("GCC diagnostic push")						\
+	_Pragma("GCC diagnostic ignored \"-Wint-conversion\"")			\
+	___bpf_fill(___param, args);						\
+	_Pragma("GCC diagnostic pop")						\
+
+/*
+ * scx_bpf_exit() wraps the scx_bpf_exit_bstr() kfunc with variadic arguments
+ * instead of an array of u64. Using this macro will cause the scheduler to
+ * exit cleanly with the specified exit code being passed to user space.
+ */
+#define scx_bpf_exit(code, fmt, args...)					\
+({										\
+	scx_bpf_bstr_preamble(fmt, args)					\
+	scx_bpf_exit_bstr(code, ___fmt, ___param, sizeof(___param));		\
+	___scx_bpf_bstr_format_checker(fmt, ##args);				\
+})
+
+/*
+ * scx_bpf_error() wraps the scx_bpf_error_bstr() kfunc with variadic arguments
+ * instead of an array of u64. Invoking this macro will cause the scheduler to
+ * exit in an erroneous state, with diagnostic information being passed to the
+ * user.
+ */
+#define scx_bpf_error(fmt, args...)						\
+({										\
+	scx_bpf_bstr_preamble(fmt, args)					\
+	scx_bpf_error_bstr(___fmt, ___param, sizeof(___param));			\
+	___scx_bpf_bstr_format_checker(fmt, ##args);				\
+})
+
+/*
+ * scx_bpf_dump() wraps the scx_bpf_dump_bstr() kfunc with variadic arguments
+ * instead of an array of u64. To be used from ops.dump() and friends.
+ */
+#define scx_bpf_dump(fmt, args...)						\
+({										\
+	scx_bpf_bstr_preamble(fmt, args)					\
+	scx_bpf_dump_bstr(___fmt, ___param, sizeof(___param));			\
+	___scx_bpf_bstr_format_checker(fmt, ##args);				\
+})
+
+#define BPF_STRUCT_OPS(name, args...)						\
+SEC("struct_ops/"#name)								\
+BPF_PROG(name, ##args)
+
+#define BPF_STRUCT_OPS_SLEEPABLE(name, args...)					\
+SEC("struct_ops.s/"#name)							\
+BPF_PROG(name, ##args)
+
+/**
+ * RESIZABLE_ARRAY - Generates annotations for an array that may be resized
+ * @elfsec: the data section of the BPF program in which to place the array
+ * @arr: the name of the array
+ *
+ * libbpf has an API for setting map value sizes. Since data sections (i.e.
+ * bss, data, rodata) themselves are maps, a data section can be resized. If
+ * a data section has an array as its last element, the BTF info for that
+ * array will be adjusted so that length of the array is extended to meet the
+ * new length of the data section. This macro annotates an array to have an
+ * element count of one with the assumption that this array can be resized
+ * within the userspace program. It also annotates the section specifier so
+ * this array exists in a custom sub data section which can be resized
+ * independently.
+ *
+ * See RESIZE_ARRAY() for the userspace convenience macro for resizing an
+ * array declared with RESIZABLE_ARRAY().
+ */
+#define RESIZABLE_ARRAY(elfsec, arr) arr[1] SEC("."#elfsec"."#arr)
+
+/**
+ * MEMBER_VPTR - Obtain the verified pointer to a struct or array member
+ * @base: struct or array to index
+ * @member: dereferenced member (e.g. .field, [idx0][idx1], .field[idx0] ...)
+ *
+ * The verifier often gets confused by the instruction sequence the compiler
+ * generates for indexing struct fields or arrays. This macro forces the
+ * compiler to generate a code sequence which first calculates the byte offset,
+ * checks it against the struct or array size and add that byte offset to
+ * generate the pointer to the member to help the verifier.
+ *
+ * Ideally, we want to abort if the calculated offset is out-of-bounds. However,
+ * BPF currently doesn't support abort, so evaluate to %NULL instead. The caller
+ * must check for %NULL and take appropriate action to appease the verifier. To
+ * avoid confusing the verifier, it's best to check for %NULL and dereference
+ * immediately.
+ *
+ *	vptr = MEMBER_VPTR(my_array, [i][j]);
+ *	if (!vptr)
+ *		return error;
+ *	*vptr = new_value;
+ *
+ * sizeof(@base) should encompass the memory area to be accessed and thus can't
+ * be a pointer to the area. Use `MEMBER_VPTR(*ptr, .member)` instead of
+ * `MEMBER_VPTR(ptr, ->member)`.
+ */
+#define MEMBER_VPTR(base, member) (typeof((base) member) *)			\
+({										\
+	u64 __base = (u64)&(base);						\
+	u64 __addr = (u64)&((base) member) - __base;				\
+	_Static_assert(sizeof(base) >= sizeof((base) member),			\
+		       "@base is smaller than @member, is @base a pointer?");	\
+	asm volatile (								\
+		"if %0 <= %[max] goto +2\n"					\
+		"%0 = 0\n"							\
+		"goto +1\n"							\
+		"%0 += %1\n"							\
+		: "+r"(__addr)							\
+		: "r"(__base),							\
+		  [max]"i"(sizeof(base) - sizeof((base) member)));		\
+	__addr;									\
+})
+
+/**
+ * ARRAY_ELEM_PTR - Obtain the verified pointer to an array element
+ * @arr: array to index into
+ * @i: array index
+ * @n: number of elements in array
+ *
+ * Similar to MEMBER_VPTR() but is intended for use with arrays where the
+ * element count needs to be explicit.
+ * It can be used in cases where a global array is defined with an initial
+ * size but is intended to be be resized before loading the BPF program.
+ * Without this version of the macro, MEMBER_VPTR() will use the compile time
+ * size of the array to compute the max, which will result in rejection by
+ * the verifier.
+ */
+#define ARRAY_ELEM_PTR(arr, i, n) (typeof(arr[i]) *)				\
+({										\
+	u64 __base = (u64)arr;							\
+	u64 __addr = (u64)&(arr[i]) - __base;					\
+	asm volatile (								\
+		"if %0 <= %[max] goto +2\n"					\
+		"%0 = 0\n"							\
+		"goto +1\n"							\
+		"%0 += %1\n"							\
+		: "+r"(__addr)							\
+		: "r"(__base),							\
+		  [max]"r"(sizeof(arr[0]) * ((n) - 1)));			\
+	__addr;									\
+})
+
+
+/*
+ * BPF declarations and helpers
+ */
+
+/* list and rbtree */
+#define __contains(name, node) __attribute__((btf_decl_tag("contains:" #name ":" #node)))
+#define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
+
+void *bpf_obj_new_impl(__u64 local_type_id, void *meta) __ksym;
+void bpf_obj_drop_impl(void *kptr, void *meta) __ksym;
+
+#define bpf_obj_new(type) ((type *)bpf_obj_new_impl(bpf_core_type_id_local(type), NULL))
+#define bpf_obj_drop(kptr) bpf_obj_drop_impl(kptr, NULL)
+
+void bpf_list_push_front(struct bpf_list_head *head, struct bpf_list_node *node) __ksym;
+void bpf_list_push_back(struct bpf_list_head *head, struct bpf_list_node *node) __ksym;
+struct bpf_list_node *bpf_list_pop_front(struct bpf_list_head *head) __ksym;
+struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head) __ksym;
+struct bpf_rb_node *bpf_rbtree_remove(struct bpf_rb_root *root,
+				      struct bpf_rb_node *node) __ksym;
+int bpf_rbtree_add_impl(struct bpf_rb_root *root, struct bpf_rb_node *node,
+			bool (less)(struct bpf_rb_node *a, const struct bpf_rb_node *b),
+			void *meta, __u64 off) __ksym;
+#define bpf_rbtree_add(head, node, less) bpf_rbtree_add_impl(head, node, less, NULL, 0)
+
+struct bpf_rb_node *bpf_rbtree_first(struct bpf_rb_root *root) __ksym;
+
+void *bpf_refcount_acquire_impl(void *kptr, void *meta) __ksym;
+#define bpf_refcount_acquire(kptr) bpf_refcount_acquire_impl(kptr, NULL)
+
+/* task */
+struct task_struct *bpf_task_from_pid(s32 pid) __ksym;
+struct task_struct *bpf_task_acquire(struct task_struct *p) __ksym;
+void bpf_task_release(struct task_struct *p) __ksym;
+
+/* cgroup */
+struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level) __ksym;
+void bpf_cgroup_release(struct cgroup *cgrp) __ksym;
+struct cgroup *bpf_cgroup_from_id(u64 cgid) __ksym;
+
+/* css iteration */
+struct bpf_iter_css;
+struct cgroup_subsys_state;
+extern int bpf_iter_css_new(struct bpf_iter_css *it,
+			    struct cgroup_subsys_state *start,
+			    unsigned int flags) __weak __ksym;
+extern struct cgroup_subsys_state *
+bpf_iter_css_next(struct bpf_iter_css *it) __weak __ksym;
+extern void bpf_iter_css_destroy(struct bpf_iter_css *it) __weak __ksym;
+
+/* cpumask */
+struct bpf_cpumask *bpf_cpumask_create(void) __ksym;
+struct bpf_cpumask *bpf_cpumask_acquire(struct bpf_cpumask *cpumask) __ksym;
+void bpf_cpumask_release(struct bpf_cpumask *cpumask) __ksym;
+u32 bpf_cpumask_first(const struct cpumask *cpumask) __ksym;
+u32 bpf_cpumask_first_zero(const struct cpumask *cpumask) __ksym;
+void bpf_cpumask_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
+void bpf_cpumask_clear_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
+bool bpf_cpumask_test_cpu(u32 cpu, const struct cpumask *cpumask) __ksym;
+bool bpf_cpumask_test_and_set_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
+bool bpf_cpumask_test_and_clear_cpu(u32 cpu, struct bpf_cpumask *cpumask) __ksym;
+void bpf_cpumask_setall(struct bpf_cpumask *cpumask) __ksym;
+void bpf_cpumask_clear(struct bpf_cpumask *cpumask) __ksym;
+bool bpf_cpumask_and(struct bpf_cpumask *dst, const struct cpumask *src1,
+		     const struct cpumask *src2) __ksym;
+void bpf_cpumask_or(struct bpf_cpumask *dst, const struct cpumask *src1,
+		    const struct cpumask *src2) __ksym;
+void bpf_cpumask_xor(struct bpf_cpumask *dst, const struct cpumask *src1,
+		     const struct cpumask *src2) __ksym;
+bool bpf_cpumask_equal(const struct cpumask *src1, const struct cpumask *src2) __ksym;
+bool bpf_cpumask_intersects(const struct cpumask *src1, const struct cpumask *src2) __ksym;
+bool bpf_cpumask_subset(const struct cpumask *src1, const struct cpumask *src2) __ksym;
+bool bpf_cpumask_empty(const struct cpumask *cpumask) __ksym;
+bool bpf_cpumask_full(const struct cpumask *cpumask) __ksym;
+void bpf_cpumask_copy(struct bpf_cpumask *dst, const struct cpumask *src) __ksym;
+u32 bpf_cpumask_any_distribute(const struct cpumask *cpumask) __ksym;
+u32 bpf_cpumask_any_and_distribute(const struct cpumask *src1,
+				   const struct cpumask *src2) __ksym;
+
+/* rcu */
+void bpf_rcu_read_lock(void) __ksym;
+void bpf_rcu_read_unlock(void) __ksym;
+
+
+/*
+ * Other helpers
+ */
+
+/* useful compiler attributes */
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#define __maybe_unused __attribute__((__unused__))
+
+/*
+ * READ/WRITE_ONCE() are from kernel (include/asm-generic/rwonce.h). They
+ * prevent compiler from caching, redoing or reordering reads or writes.
+ */
+typedef __u8  __attribute__((__may_alias__))  __u8_alias_t;
+typedef __u16 __attribute__((__may_alias__)) __u16_alias_t;
+typedef __u32 __attribute__((__may_alias__)) __u32_alias_t;
+typedef __u64 __attribute__((__may_alias__)) __u64_alias_t;
+
+static __always_inline void __read_once_size(const volatile void *p, void *res, int size)
+{
+	switch (size) {
+	case 1: *(__u8_alias_t  *) res = *(volatile __u8_alias_t  *) p; break;
+	case 2: *(__u16_alias_t *) res = *(volatile __u16_alias_t *) p; break;
+	case 4: *(__u32_alias_t *) res = *(volatile __u32_alias_t *) p; break;
+	case 8: *(__u64_alias_t *) res = *(volatile __u64_alias_t *) p; break;
+	default:
+		barrier();
+		__builtin_memcpy((void *)res, (const void *)p, size);
+		barrier();
+	}
+}
+
+static __always_inline void __write_once_size(volatile void *p, void *res, int size)
+{
+	switch (size) {
+	case 1: *(volatile  __u8_alias_t *) p = *(__u8_alias_t  *) res; break;
+	case 2: *(volatile __u16_alias_t *) p = *(__u16_alias_t *) res; break;
+	case 4: *(volatile __u32_alias_t *) p = *(__u32_alias_t *) res; break;
+	case 8: *(volatile __u64_alias_t *) p = *(__u64_alias_t *) res; break;
+	default:
+		barrier();
+		__builtin_memcpy((void *)p, (const void *)res, size);
+		barrier();
+	}
+}
+
+#define READ_ONCE(x)					\
+({							\
+	union { typeof(x) __val; char __c[1]; } __u =	\
+		{ .__c = { 0 } };			\
+	__read_once_size(&(x), __u.__c, sizeof(x));	\
+	__u.__val;					\
+})
+
+#define WRITE_ONCE(x, val)				\
+({							\
+	union { typeof(x) __val; char __c[1]; } __u =	\
+		{ .__val = (val) }; 			\
+	__write_once_size(&(x), __u.__c, sizeof(x));	\
+	__u.__val;					\
+})
+
+/*
+ * log2_u32 - Compute the base 2 logarithm of a 32-bit exponential value.
+ * @v: The value for which we're computing the base 2 logarithm.
+ */
+static inline u32 log2_u32(u32 v)
+{
+        u32 r;
+        u32 shift;
+
+        r = (v > 0xFFFF) << 4; v >>= r;
+        shift = (v > 0xFF) << 3; v >>= shift; r |= shift;
+        shift = (v > 0xF) << 2; v >>= shift; r |= shift;
+        shift = (v > 0x3) << 1; v >>= shift; r |= shift;
+        r |= (v >> 1);
+        return r;
+}
+
+/*
+ * log2_u64 - Compute the base 2 logarithm of a 64-bit exponential value.
+ * @v: The value for which we're computing the base 2 logarithm.
+ */
+static inline u32 log2_u64(u64 v)
+{
+        u32 hi = v >> 32;
+        if (hi)
+                return log2_u32(hi) + 32 + 1;
+        else
+                return log2_u32(v) + 1;
+}
+
+#include "compat.bpf.h"
+
+#endif	/* __SCX_COMMON_BPF_H */
diff --git a/tools/sched_ext/include/scx/common.h b/tools/sched_ext/include/scx/common.h
new file mode 100644
index 000000000000..5b0f90152152
--- /dev/null
+++ b/tools/sched_ext/include/scx/common.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ */
+#ifndef __SCHED_EXT_COMMON_H
+#define __SCHED_EXT_COMMON_H
+
+#ifdef __KERNEL__
+#error "Should not be included by BPF programs"
+#endif
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <errno.h>
+
+typedef uint8_t u8;
+typedef uint16_t u16;
+typedef uint32_t u32;
+typedef uint64_t u64;
+typedef int8_t s8;
+typedef int16_t s16;
+typedef int32_t s32;
+typedef int64_t s64;
+
+#define SCX_BUG(__fmt, ...)							\
+	do {									\
+		fprintf(stderr, "[SCX_BUG] %s:%d", __FILE__, __LINE__);		\
+		if (errno)							\
+			fprintf(stderr, " (%s)\n", strerror(errno));		\
+		else								\
+			fprintf(stderr, "\n");					\
+		fprintf(stderr, __fmt __VA_OPT__(,) __VA_ARGS__);		\
+		fprintf(stderr, "\n");						\
+										\
+		exit(EXIT_FAILURE);						\
+	} while (0)
+
+#define SCX_BUG_ON(__cond, __fmt, ...)					\
+	do {								\
+		if (__cond)						\
+			SCX_BUG((__fmt) __VA_OPT__(,) __VA_ARGS__);	\
+	} while (0)
+
+/**
+ * RESIZE_ARRAY - Convenience macro for resizing a BPF array
+ * @__skel: the skeleton containing the array
+ * @elfsec: the data section of the BPF program in which the array exists
+ * @arr: the name of the array
+ * @n: the desired array element count
+ *
+ * For BPF arrays declared with RESIZABLE_ARRAY(), this macro performs two
+ * operations. It resizes the map which corresponds to the custom data
+ * section that contains the target array. As a side effect, the BTF info for
+ * the array is adjusted so that the array length is sized to cover the new
+ * data section size. The second operation is reassigning the skeleton pointer
+ * for that custom data section so that it points to the newly memory mapped
+ * region.
+ */
+#define RESIZE_ARRAY(__skel, elfsec, arr, n)						\
+	do {										\
+		size_t __sz;								\
+		bpf_map__set_value_size((__skel)->maps.elfsec##_##arr,			\
+				sizeof((__skel)->elfsec##_##arr->arr[0]) * (n));	\
+		(__skel)->elfsec##_##arr =						\
+			bpf_map__initial_value((__skel)->maps.elfsec##_##arr, &__sz);	\
+	} while (0)
+
+#include "user_exit_info.h"
+#include "compat.h"
+
+#endif	/* __SCHED_EXT_COMMON_H */
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
new file mode 100644
index 000000000000..3d2fe1208900
--- /dev/null
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#ifndef __SCX_COMPAT_BPF_H
+#define __SCX_COMPAT_BPF_H
+
+#define __COMPAT_ENUM_OR_ZERO(__type, __ent)					\
+({										\
+	__type __ret = 0;							\
+	if (bpf_core_enum_value_exists(__type, __ent))				\
+		__ret = __ent;							\
+	__ret;									\
+})
+
+/*
+ * Define sched_ext_ops. This may be expanded to define multiple variants for
+ * backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
+ */
+#define SCX_OPS_DEFINE(__name, ...)						\
+	SEC(".struct_ops.link")							\
+	struct sched_ext_ops __name = {						\
+		__VA_ARGS__,							\
+	};
+
+#endif	/* __SCX_COMPAT_BPF_H */
diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
new file mode 100644
index 000000000000..1bf8eddf20c2
--- /dev/null
+++ b/tools/sched_ext/include/scx/compat.h
@@ -0,0 +1,187 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#ifndef __SCX_COMPAT_H
+#define __SCX_COMPAT_H
+
+#include <bpf/btf.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+struct btf *__COMPAT_vmlinux_btf __attribute__((weak));
+
+static inline void __COMPAT_load_vmlinux_btf(void)
+{
+	if (!__COMPAT_vmlinux_btf) {
+		__COMPAT_vmlinux_btf = btf__load_vmlinux_btf();
+		SCX_BUG_ON(!__COMPAT_vmlinux_btf, "btf__load_vmlinux_btf()");
+	}
+}
+
+static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v)
+{
+	const struct btf_type *t;
+	const char *n;
+	s32 tid;
+	int i;
+
+	__COMPAT_load_vmlinux_btf();
+
+	tid = btf__find_by_name(__COMPAT_vmlinux_btf, type);
+	if (tid < 0)
+		return false;
+
+	t = btf__type_by_id(__COMPAT_vmlinux_btf, tid);
+	SCX_BUG_ON(!t, "btf__type_by_id(%d)", tid);
+
+	if (btf_is_enum(t)) {
+		struct btf_enum *e = btf_enum(t);
+
+		for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
+			n = btf__name_by_offset(__COMPAT_vmlinux_btf, e[i].name_off);
+			SCX_BUG_ON(!n, "btf__name_by_offset()");
+			if (!strcmp(n, name)) {
+				*v = e[i].val;
+				return true;
+			}
+		}
+	} else if (btf_is_enum64(t)) {
+		struct btf_enum64 *e = btf_enum64(t);
+
+		for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
+			n = btf__name_by_offset(__COMPAT_vmlinux_btf, e[i].name_off);
+			SCX_BUG_ON(!n, "btf__name_by_offset()");
+			if (!strcmp(n, name)) {
+				*v = btf_enum64_value(&e[i]);
+				return true;
+			}
+		}
+	}
+
+	return false;
+}
+
+#define __COMPAT_ENUM_OR_ZERO(__type, __ent)					\
+({										\
+	u64 __val = 0;								\
+	__COMPAT_read_enum(__type, __ent, &__val);				\
+	__val;									\
+})
+
+static inline bool __COMPAT_has_ksym(const char *ksym)
+{
+	__COMPAT_load_vmlinux_btf();
+	return btf__find_by_name(__COMPAT_vmlinux_btf, ksym) >= 0;
+}
+
+static inline bool __COMPAT_struct_has_field(const char *type, const char *field)
+{
+	const struct btf_type *t;
+	const struct btf_member *m;
+	const char *n;
+	s32 tid;
+	int i;
+
+	__COMPAT_load_vmlinux_btf();
+	tid = btf__find_by_name_kind(__COMPAT_vmlinux_btf, type, BTF_KIND_STRUCT);
+	if (tid < 0)
+		return false;
+
+	t = btf__type_by_id(__COMPAT_vmlinux_btf, tid);
+	SCX_BUG_ON(!t, "btf__type_by_id(%d)", tid);
+
+	m = btf_members(t);
+
+	for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
+		n = btf__name_by_offset(__COMPAT_vmlinux_btf, m[i].name_off);
+		SCX_BUG_ON(!n, "btf__name_by_offset()");
+			if (!strcmp(n, field))
+				return true;
+	}
+
+	return false;
+}
+
+#define SCX_OPS_SWITCH_PARTIAL							\
+	__COMPAT_ENUM_OR_ZERO("scx_ops_flags", "SCX_OPS_SWITCH_PARTIAL")
+
+static inline long scx_hotplug_seq(void)
+{
+	int fd;
+	char buf[32];
+	ssize_t len;
+	long val;
+
+	fd = open("/sys/kernel/sched_ext/hotplug_seq", O_RDONLY);
+	if (fd < 0)
+		return -ENOENT;
+
+	len = read(fd, buf, sizeof(buf) - 1);
+	SCX_BUG_ON(len <= 0, "read failed (%ld)", len);
+	buf[len] = 0;
+	close(fd);
+
+	val = strtoul(buf, NULL, 10);
+	SCX_BUG_ON(val < 0, "invalid num hotplug events: %lu", val);
+
+	return val;
+}
+
+/*
+ * struct sched_ext_ops can change over time. If compat.bpf.h::SCX_OPS_DEFINE()
+ * is used to define ops and compat.h::SCX_OPS_LOAD/ATTACH() are used to load
+ * and attach it, backward compatibility is automatically maintained where
+ * reasonable.
+ *
+ * ec7e3b0463e1 ("implement-ops") in https://github.com/sched-ext/sched_ext is
+ * the current minimum required kernel version.
+ */
+#define SCX_OPS_OPEN(__ops_name, __scx_name) ({					\
+	struct __scx_name *__skel;						\
+										\
+	SCX_BUG_ON(!__COMPAT_struct_has_field("sched_ext_ops", "dump"),		\
+		   "sched_ext_ops.dump() missing, kernel too old?");		\
+										\
+	__skel = __scx_name##__open();						\
+	SCX_BUG_ON(!__skel, "Could not open " #__scx_name);			\
+	__skel->struct_ops.__ops_name->hotplug_seq = scx_hotplug_seq();		\
+	__skel; 								\
+})
+
+#define SCX_OPS_LOAD(__skel, __ops_name, __scx_name, __uei_name) ({		\
+	UEI_SET_SIZE(__skel, __ops_name, __uei_name);				\
+	SCX_BUG_ON(__scx_name##__load((__skel)), "Failed to load skel");	\
+})
+
+/*
+ * New versions of bpftool now emit additional link placeholders for BPF maps,
+ * and set up BPF skeleton in such a way that libbpf will auto-attach BPF maps
+ * automatically, assumming libbpf is recent enough (v1.5+). Old libbpf will do
+ * nothing with those links and won't attempt to auto-attach maps.
+ *
+ * To maintain compatibility with older libbpf while avoiding trying to attach
+ * twice, disable the autoattach feature on newer libbpf.
+ */
+/* BACKPORT - bpf_mpa__set_autoattach() not available yet, commented out */
+/*#if LIBBPF_MAJOR_VERSION > 1 ||					\
+	(LIBBPF_MAJOR_VERSION == 1 && LIBBPF_MINOR_VERSION >= 5)
+#define __SCX_OPS_DISABLE_AUTOATTACH(__skel, __ops_name)			\
+	bpf_map__set_autoattach((__skel)->maps.__ops_name, false)
+#else*/
+#define __SCX_OPS_DISABLE_AUTOATTACH(__skel, __ops_name) do {} while (0)
+/*#endif*/
+
+#define SCX_OPS_ATTACH(__skel, __ops_name, __scx_name) ({			\
+	struct bpf_link *__link;						\
+	__SCX_OPS_DISABLE_AUTOATTACH(__skel, __ops_name);			\
+	SCX_BUG_ON(__scx_name##__attach((__skel)), "Failed to attach skel");	\
+	__link = bpf_map__attach_struct_ops((__skel)->maps.__ops_name);		\
+	SCX_BUG_ON(!__link, "Failed to attach struct_ops");			\
+	__link;									\
+})
+
+#endif	/* __SCX_COMPAT_H */
diff --git a/tools/sched_ext/include/scx/user_exit_info.h b/tools/sched_ext/include/scx/user_exit_info.h
new file mode 100644
index 000000000000..891693ee604e
--- /dev/null
+++ b/tools/sched_ext/include/scx/user_exit_info.h
@@ -0,0 +1,111 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Define struct user_exit_info which is shared between BPF and userspace parts
+ * to communicate exit status and other information.
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#ifndef __USER_EXIT_INFO_H
+#define __USER_EXIT_INFO_H
+
+enum uei_sizes {
+	UEI_REASON_LEN		= 128,
+	UEI_MSG_LEN		= 1024,
+	UEI_DUMP_DFL_LEN	= 32768,
+};
+
+struct user_exit_info {
+	int		kind;
+	s64		exit_code;
+	char		reason[UEI_REASON_LEN];
+	char		msg[UEI_MSG_LEN];
+};
+
+#ifdef __bpf__
+
+#include "vmlinux.h"
+#include <bpf/bpf_core_read.h>
+
+#define UEI_DEFINE(__name)							\
+	char RESIZABLE_ARRAY(data, __name##_dump);				\
+	const volatile u32 __name##_dump_len;					\
+	struct user_exit_info __name SEC(".data")
+
+#define UEI_RECORD(__uei_name, __ei) ({						\
+	bpf_probe_read_kernel_str(__uei_name.reason,				\
+				  sizeof(__uei_name.reason), (__ei)->reason);	\
+	bpf_probe_read_kernel_str(__uei_name.msg,				\
+				  sizeof(__uei_name.msg), (__ei)->msg);		\
+	bpf_probe_read_kernel_str(__uei_name##_dump,				\
+				  __uei_name##_dump_len, (__ei)->dump);		\
+	if (bpf_core_field_exists((__ei)->exit_code))				\
+		__uei_name.exit_code = (__ei)->exit_code;			\
+	/* use __sync to force memory barrier */				\
+	__sync_val_compare_and_swap(&__uei_name.kind, __uei_name.kind,		\
+				    (__ei)->kind);				\
+})
+
+#else	/* !__bpf__ */
+
+#include <stdio.h>
+#include <stdbool.h>
+
+/* no need to call the following explicitly if SCX_OPS_LOAD() is used */
+#define UEI_SET_SIZE(__skel, __ops_name, __uei_name) ({					\
+	u32 __len = (__skel)->struct_ops.__ops_name->exit_dump_len ?: UEI_DUMP_DFL_LEN;	\
+	(__skel)->rodata->__uei_name##_dump_len = __len;				\
+	RESIZE_ARRAY((__skel), data, __uei_name##_dump, __len);				\
+})
+
+#define UEI_EXITED(__skel, __uei_name) ({					\
+	/* use __sync to force memory barrier */				\
+	__sync_val_compare_and_swap(&(__skel)->data->__uei_name.kind, -1, -1);	\
+})
+
+#define UEI_REPORT(__skel, __uei_name) ({					\
+	struct user_exit_info *__uei = &(__skel)->data->__uei_name;		\
+	char *__uei_dump = (__skel)->data_##__uei_name##_dump->__uei_name##_dump; \
+	if (__uei_dump[0] != '\0') {						\
+		fputs("\nDEBUG DUMP\n", stderr);				\
+		fputs("================================================================================\n\n", stderr); \
+		fputs(__uei_dump, stderr);					\
+		fputs("\n================================================================================\n\n", stderr); \
+	}									\
+	fprintf(stderr, "EXIT: %s", __uei->reason);				\
+	if (__uei->msg[0] != '\0')						\
+		fprintf(stderr, " (%s)", __uei->msg);				\
+	fputs("\n", stderr);							\
+	__uei->exit_code;							\
+})
+
+/*
+ * We can't import vmlinux.h while compiling user C code. Let's duplicate
+ * scx_exit_code definition.
+ */
+enum scx_exit_code {
+	/* Reasons */
+	SCX_ECODE_RSN_HOTPLUG		= 1LLU << 32,
+
+	/* Actions */
+	SCX_ECODE_ACT_RESTART		= 1LLU << 48,
+};
+
+enum uei_ecode_mask {
+	UEI_ECODE_USER_MASK		= ((1LLU << 32) - 1),
+	UEI_ECODE_SYS_RSN_MASK		= ((1LLU << 16) - 1) << 32,
+	UEI_ECODE_SYS_ACT_MASK		= ((1LLU << 16) - 1) << 48,
+};
+
+/*
+ * These macro interpret the ecode returned from UEI_REPORT().
+ */
+#define UEI_ECODE_USER(__ecode)		((__ecode) & UEI_ECODE_USER_MASK)
+#define UEI_ECODE_SYS_RSN(__ecode)	((__ecode) & UEI_ECODE_SYS_RSN_MASK)
+#define UEI_ECODE_SYS_ACT(__ecode)	((__ecode) & UEI_ECODE_SYS_ACT_MASK)
+
+#define UEI_ECODE_RESTART(__ecode)	(UEI_ECODE_SYS_ACT((__ecode)) == SCX_ECODE_ACT_RESTART)
+
+#endif	/* __bpf__ */
+#endif	/* __USER_EXIT_INFO_H */
diff --git a/tools/sched_ext/scx_central.bpf.c b/tools/sched_ext/scx_central.bpf.c
new file mode 100644
index 000000000000..1d8fd570eaa7
--- /dev/null
+++ b/tools/sched_ext/scx_central.bpf.c
@@ -0,0 +1,361 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A central FIFO sched_ext scheduler which demonstrates the followings:
+ *
+ * a. Making all scheduling decisions from one CPU:
+ *
+ *    The central CPU is the only one making scheduling decisions. All other
+ *    CPUs kick the central CPU when they run out of tasks to run.
+ *
+ *    There is one global BPF queue and the central CPU schedules all CPUs by
+ *    dispatching from the global queue to each CPU's local dsq from dispatch().
+ *    This isn't the most straightforward. e.g. It'd be easier to bounce
+ *    through per-CPU BPF queues. The current design is chosen to maximally
+ *    utilize and verify various SCX mechanisms such as LOCAL_ON dispatching.
+ *
+ * b. Tickless operation
+ *
+ *    All tasks are dispatched with the infinite slice which allows stopping the
+ *    ticks on CONFIG_NO_HZ_FULL kernels running with the proper nohz_full
+ *    parameter. The tickless operation can be observed through
+ *    /proc/interrupts.
+ *
+ *    Periodic switching is enforced by a periodic timer checking all CPUs and
+ *    preempting them as necessary. Unfortunately, BPF timer currently doesn't
+ *    have a way to pin to a specific CPU, so the periodic timer isn't pinned to
+ *    the central CPU.
+ *
+ * c. Preemption
+ *
+ *    Kthreads are unconditionally queued to the head of a matching local dsq
+ *    and dispatched with SCX_DSQ_PREEMPT. This ensures that a kthread is always
+ *    prioritized over user threads, which is required for ensuring forward
+ *    progress as e.g. the periodic timer may run on a ksoftirqd and if the
+ *    ksoftirqd gets starved by a user thread, there may not be anything else to
+ *    vacate that user thread.
+ *
+ *    SCX_KICK_PREEMPT is used to trigger scheduling and CPUs to move to the
+ *    next tasks.
+ *
+ * This scheduler is designed to maximize usage of various SCX mechanisms. A
+ * more practical implementation would likely put the scheduling loop outside
+ * the central CPU's dispatch() path and add some form of priority mechanism.
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+enum {
+	FALLBACK_DSQ_ID		= 0,
+	MS_TO_NS		= 1000LLU * 1000,
+	TIMER_INTERVAL_NS	= 1 * MS_TO_NS,
+};
+
+const volatile s32 central_cpu;
+const volatile u32 nr_cpu_ids = 1;	/* !0 for veristat, set during init */
+const volatile u64 slice_ns = SCX_SLICE_DFL;
+
+bool timer_pinned = true;
+u64 nr_total, nr_locals, nr_queued, nr_lost_pids;
+u64 nr_timers, nr_dispatches, nr_mismatches, nr_retries;
+u64 nr_overflows;
+
+UEI_DEFINE(uei);
+
+struct {
+	__uint(type, BPF_MAP_TYPE_QUEUE);
+	__uint(max_entries, 4096);
+	__type(value, s32);
+} central_q SEC(".maps");
+
+/* can't use percpu map due to bad lookups */
+bool RESIZABLE_ARRAY(data, cpu_gimme_task);
+u64 RESIZABLE_ARRAY(data, cpu_started_at);
+
+struct central_timer {
+	struct bpf_timer timer;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct central_timer);
+} central_timer SEC(".maps");
+
+static bool vtime_before(u64 a, u64 b)
+{
+	return (s64)(a - b) < 0;
+}
+
+s32 BPF_STRUCT_OPS(central_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	/*
+	 * Steer wakeups to the central CPU as much as possible to avoid
+	 * disturbing other CPUs. It's safe to blindly return the central cpu as
+	 * select_cpu() is a hint and if @p can't be on it, the kernel will
+	 * automatically pick a fallback CPU.
+	 */
+	return central_cpu;
+}
+
+void BPF_STRUCT_OPS(central_enqueue, struct task_struct *p, u64 enq_flags)
+{
+	s32 pid = p->pid;
+
+	__sync_fetch_and_add(&nr_total, 1);
+
+	/*
+	 * Push per-cpu kthreads at the head of local dsq's and preempt the
+	 * corresponding CPU. This ensures that e.g. ksoftirqd isn't blocked
+	 * behind other threads which is necessary for forward progress
+	 * guarantee as we depend on the BPF timer which may run from ksoftirqd.
+	 */
+	if ((p->flags & PF_KTHREAD) && p->nr_cpus_allowed == 1) {
+		__sync_fetch_and_add(&nr_locals, 1);
+		scx_bpf_dispatch(p, SCX_DSQ_LOCAL, SCX_SLICE_INF,
+				 enq_flags | SCX_ENQ_PREEMPT);
+		return;
+	}
+
+	if (bpf_map_push_elem(&central_q, &pid, 0)) {
+		__sync_fetch_and_add(&nr_overflows, 1);
+		scx_bpf_dispatch(p, FALLBACK_DSQ_ID, SCX_SLICE_INF, enq_flags);
+		return;
+	}
+
+	__sync_fetch_and_add(&nr_queued, 1);
+
+	if (!scx_bpf_task_running(p))
+		scx_bpf_kick_cpu(central_cpu, SCX_KICK_PREEMPT);
+}
+
+static bool dispatch_to_cpu(s32 cpu)
+{
+	struct task_struct *p;
+	s32 pid;
+
+	bpf_repeat(BPF_MAX_LOOPS) {
+		if (bpf_map_pop_elem(&central_q, &pid))
+			break;
+
+		__sync_fetch_and_sub(&nr_queued, 1);
+
+		p = bpf_task_from_pid(pid);
+		if (!p) {
+			__sync_fetch_and_add(&nr_lost_pids, 1);
+			continue;
+		}
+
+		/*
+		 * If we can't run the task at the top, do the dumb thing and
+		 * bounce it to the fallback dsq.
+		 */
+		if (!bpf_cpumask_test_cpu(cpu, p->cpus_ptr)) {
+			__sync_fetch_and_add(&nr_mismatches, 1);
+			scx_bpf_dispatch(p, FALLBACK_DSQ_ID, SCX_SLICE_INF, 0);
+			bpf_task_release(p);
+			/*
+			 * We might run out of dispatch buffer slots if we continue dispatching
+			 * to the fallback DSQ, without dispatching to the local DSQ of the
+			 * target CPU. In such a case, break the loop now as will fail the
+			 * next dispatch operation.
+			 */
+			if (!scx_bpf_dispatch_nr_slots())
+				break;
+			continue;
+		}
+
+		/* dispatch to local and mark that @cpu doesn't need more */
+		scx_bpf_dispatch(p, SCX_DSQ_LOCAL_ON | cpu, SCX_SLICE_INF, 0);
+
+		if (cpu != central_cpu)
+			scx_bpf_kick_cpu(cpu, SCX_KICK_IDLE);
+
+		bpf_task_release(p);
+		return true;
+	}
+
+	return false;
+}
+
+void BPF_STRUCT_OPS(central_dispatch, s32 cpu, struct task_struct *prev)
+{
+	if (cpu == central_cpu) {
+		/* dispatch for all other CPUs first */
+		__sync_fetch_and_add(&nr_dispatches, 1);
+
+		bpf_for(cpu, 0, nr_cpu_ids) {
+			bool *gimme;
+
+			if (!scx_bpf_dispatch_nr_slots())
+				break;
+
+			/* central's gimme is never set */
+			gimme = ARRAY_ELEM_PTR(cpu_gimme_task, cpu, nr_cpu_ids);
+			if (gimme && !*gimme)
+				continue;
+
+			if (dispatch_to_cpu(cpu))
+				*gimme = false;
+		}
+
+		/*
+		 * Retry if we ran out of dispatch buffer slots as we might have
+		 * skipped some CPUs and also need to dispatch for self. The ext
+		 * core automatically retries if the local dsq is empty but we
+		 * can't rely on that as we're dispatching for other CPUs too.
+		 * Kick self explicitly to retry.
+		 */
+		if (!scx_bpf_dispatch_nr_slots()) {
+			__sync_fetch_and_add(&nr_retries, 1);
+			scx_bpf_kick_cpu(central_cpu, SCX_KICK_PREEMPT);
+			return;
+		}
+
+		/* look for a task to run on the central CPU */
+		if (scx_bpf_consume(FALLBACK_DSQ_ID))
+			return;
+		dispatch_to_cpu(central_cpu);
+	} else {
+		bool *gimme;
+
+		if (scx_bpf_consume(FALLBACK_DSQ_ID))
+			return;
+
+		gimme = ARRAY_ELEM_PTR(cpu_gimme_task, cpu, nr_cpu_ids);
+		if (gimme)
+			*gimme = true;
+
+		/*
+		 * Force dispatch on the scheduling CPU so that it finds a task
+		 * to run for us.
+		 */
+		scx_bpf_kick_cpu(central_cpu, SCX_KICK_PREEMPT);
+	}
+}
+
+void BPF_STRUCT_OPS(central_running, struct task_struct *p)
+{
+	s32 cpu = scx_bpf_task_cpu(p);
+	u64 *started_at = ARRAY_ELEM_PTR(cpu_started_at, cpu, nr_cpu_ids);
+	if (started_at)
+		*started_at = bpf_ktime_get_ns() ?: 1;	/* 0 indicates idle */
+}
+
+void BPF_STRUCT_OPS(central_stopping, struct task_struct *p, bool runnable)
+{
+	s32 cpu = scx_bpf_task_cpu(p);
+	u64 *started_at = ARRAY_ELEM_PTR(cpu_started_at, cpu, nr_cpu_ids);
+	if (started_at)
+		*started_at = 0;
+}
+
+static int central_timerfn(void *map, int *key, struct bpf_timer *timer)
+{
+	u64 now = bpf_ktime_get_ns();
+	u64 nr_to_kick = nr_queued;
+	s32 i, curr_cpu;
+
+	curr_cpu = bpf_get_smp_processor_id();
+	if (timer_pinned && (curr_cpu != central_cpu)) {
+		scx_bpf_error("Central timer ran on CPU %d, not central CPU %d",
+			      curr_cpu, central_cpu);
+		return 0;
+	}
+
+	bpf_for(i, 0, nr_cpu_ids) {
+		s32 cpu = (nr_timers + i) % nr_cpu_ids;
+		u64 *started_at;
+
+		if (cpu == central_cpu)
+			continue;
+
+		/* kick iff the current one exhausted its slice */
+		started_at = ARRAY_ELEM_PTR(cpu_started_at, cpu, nr_cpu_ids);
+		if (started_at && *started_at &&
+		    vtime_before(now, *started_at + slice_ns))
+			continue;
+
+		/* and there's something pending */
+		if (scx_bpf_dsq_nr_queued(FALLBACK_DSQ_ID) ||
+		    scx_bpf_dsq_nr_queued(SCX_DSQ_LOCAL_ON | cpu))
+			;
+		else if (nr_to_kick)
+			nr_to_kick--;
+		else
+			continue;
+
+		scx_bpf_kick_cpu(cpu, SCX_KICK_PREEMPT);
+	}
+
+	bpf_timer_start(timer, TIMER_INTERVAL_NS, BPF_F_TIMER_CPU_PIN);
+	__sync_fetch_and_add(&nr_timers, 1);
+	return 0;
+}
+
+int BPF_STRUCT_OPS_SLEEPABLE(central_init)
+{
+	u32 key = 0;
+	struct bpf_timer *timer;
+	int ret;
+
+	ret = scx_bpf_create_dsq(FALLBACK_DSQ_ID, -1);
+	if (ret)
+		return ret;
+
+	timer = bpf_map_lookup_elem(&central_timer, &key);
+	if (!timer)
+		return -ESRCH;
+
+	if (bpf_get_smp_processor_id() != central_cpu) {
+		scx_bpf_error("init from non-central CPU");
+		return -EINVAL;
+	}
+
+	bpf_timer_init(timer, &central_timer, CLOCK_MONOTONIC);
+	bpf_timer_set_callback(timer, central_timerfn);
+
+	ret = bpf_timer_start(timer, TIMER_INTERVAL_NS, BPF_F_TIMER_CPU_PIN);
+	/*
+	 * BPF_F_TIMER_CPU_PIN is pretty new (>=6.7). If we're running in a
+	 * kernel which doesn't have it, bpf_timer_start() will return -EINVAL.
+	 * Retry without the PIN. This would be the perfect use case for
+	 * bpf_core_enum_value_exists() but the enum type doesn't have a name
+	 * and can't be used with bpf_core_enum_value_exists(). Oh well...
+	 */
+	if (ret == -EINVAL) {
+		timer_pinned = false;
+		ret = bpf_timer_start(timer, TIMER_INTERVAL_NS, 0);
+	}
+	if (ret)
+		scx_bpf_error("bpf_timer_start failed (%d)", ret);
+	return ret;
+}
+
+void BPF_STRUCT_OPS(central_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SCX_OPS_DEFINE(central_ops,
+	       /*
+		* We are offloading all scheduling decisions to the central CPU
+		* and thus being the last task on a given CPU doesn't mean
+		* anything special. Enqueue the last tasks like any other tasks.
+		*/
+	       .flags			= SCX_OPS_ENQ_LAST,
+
+	       .select_cpu		= (void *)central_select_cpu,
+	       .enqueue			= (void *)central_enqueue,
+	       .dispatch		= (void *)central_dispatch,
+	       .running			= (void *)central_running,
+	       .stopping		= (void *)central_stopping,
+	       .init			= (void *)central_init,
+	       .exit			= (void *)central_exit,
+	       .name			= "central");
diff --git a/tools/sched_ext/scx_central.c b/tools/sched_ext/scx_central.c
new file mode 100644
index 000000000000..21deea320bd7
--- /dev/null
+++ b/tools/sched_ext/scx_central.c
@@ -0,0 +1,135 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <inttypes.h>
+#include <signal.h>
+#include <libgen.h>
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include "scx_central.bpf.skel.h"
+
+const char help_fmt[] =
+"A central FIFO sched_ext scheduler.\n"
+"\n"
+"See the top-level comment in .bpf.c for more details.\n"
+"\n"
+"Usage: %s [-s SLICE_US] [-c CPU]\n"
+"\n"
+"  -s SLICE_US   Override slice duration\n"
+"  -c CPU        Override the central CPU (default: 0)\n"
+"  -v            Print libbpf debug messages\n"
+"  -h            Display this help and exit\n";
+
+static bool verbose;
+static volatile int exit_req;
+
+static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
+{
+	if (level == LIBBPF_DEBUG && !verbose)
+		return 0;
+	return vfprintf(stderr, format, args);
+}
+
+static void sigint_handler(int dummy)
+{
+	exit_req = 1;
+}
+
+int main(int argc, char **argv)
+{
+	struct scx_central *skel;
+	struct bpf_link *link;
+	__u64 seq = 0, ecode;
+	__s32 opt;
+	cpu_set_t *cpuset;
+
+	libbpf_set_print(libbpf_print_fn);
+	signal(SIGINT, sigint_handler);
+	signal(SIGTERM, sigint_handler);
+restart:
+	skel = SCX_OPS_OPEN(central_ops, scx_central);
+
+	skel->rodata->central_cpu = 0;
+	skel->rodata->nr_cpu_ids = libbpf_num_possible_cpus();
+
+	while ((opt = getopt(argc, argv, "s:c:pvh")) != -1) {
+		switch (opt) {
+		case 's':
+			skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000;
+			break;
+		case 'c':
+			skel->rodata->central_cpu = strtoul(optarg, NULL, 0);
+			break;
+		case 'v':
+			verbose = true;
+			break;
+		default:
+			fprintf(stderr, help_fmt, basename(argv[0]));
+			return opt != 'h';
+		}
+	}
+
+	/* Resize arrays so their element count is equal to cpu count. */
+	RESIZE_ARRAY(skel, data, cpu_gimme_task, skel->rodata->nr_cpu_ids);
+	RESIZE_ARRAY(skel, data, cpu_started_at, skel->rodata->nr_cpu_ids);
+
+	SCX_OPS_LOAD(skel, central_ops, scx_central, uei);
+
+	/*
+	 * Affinitize the loading thread to the central CPU, as:
+	 * - That's where the BPF timer is first invoked in the BPF program.
+	 * - We probably don't want this user space component to take up a core
+	 *   from a task that would benefit from avoiding preemption on one of
+	 *   the tickless cores.
+	 *
+	 * Until BPF supports pinning the timer, it's not guaranteed that it
+	 * will always be invoked on the central CPU. In practice, this
+	 * suffices the majority of the time.
+	 */
+	cpuset = CPU_ALLOC(skel->rodata->nr_cpu_ids);
+	SCX_BUG_ON(!cpuset, "Failed to allocate cpuset");
+	CPU_ZERO(cpuset);
+	CPU_SET(skel->rodata->central_cpu, cpuset);
+	SCX_BUG_ON(sched_setaffinity(0, sizeof(cpuset), cpuset),
+		   "Failed to affinitize to central CPU %d (max %d)",
+		   skel->rodata->central_cpu, skel->rodata->nr_cpu_ids - 1);
+	CPU_FREE(cpuset);
+
+	link = SCX_OPS_ATTACH(skel, central_ops, scx_central);
+
+	if (!skel->data->timer_pinned)
+		printf("WARNING : BPF_F_TIMER_CPU_PIN not available, timer not pinned to central\n");
+
+	while (!exit_req && !UEI_EXITED(skel, uei)) {
+		printf("[SEQ %llu]\n", seq++);
+		printf("total   :%10" PRIu64 "    local:%10" PRIu64 "   queued:%10" PRIu64 "  lost:%10" PRIu64 "\n",
+		       skel->bss->nr_total,
+		       skel->bss->nr_locals,
+		       skel->bss->nr_queued,
+		       skel->bss->nr_lost_pids);
+		printf("timer   :%10" PRIu64 " dispatch:%10" PRIu64 " mismatch:%10" PRIu64 " retry:%10" PRIu64 "\n",
+		       skel->bss->nr_timers,
+		       skel->bss->nr_dispatches,
+		       skel->bss->nr_mismatches,
+		       skel->bss->nr_retries);
+		printf("overflow:%10" PRIu64 "\n",
+		       skel->bss->nr_overflows);
+		fflush(stdout);
+		sleep(1);
+	}
+
+	bpf_link__destroy(link);
+	ecode = UEI_REPORT(skel, uei);
+	scx_central__destroy(skel);
+
+	if (UEI_ECODE_RESTART(ecode))
+		goto restart;
+	return 0;
+}
diff --git a/tools/sched_ext/scx_qmap.bpf.c b/tools/sched_ext/scx_qmap.bpf.c
new file mode 100644
index 000000000000..892278f12dce
--- /dev/null
+++ b/tools/sched_ext/scx_qmap.bpf.c
@@ -0,0 +1,706 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A simple five-level FIFO queue scheduler.
+ *
+ * There are five FIFOs implemented using BPF_MAP_TYPE_QUEUE. A task gets
+ * assigned to one depending on its compound weight. Each CPU round robins
+ * through the FIFOs and dispatches more from FIFOs with higher indices - 1 from
+ * queue0, 2 from queue1, 4 from queue2 and so on.
+ *
+ * This scheduler demonstrates:
+ *
+ * - BPF-side queueing using PIDs.
+ * - Sleepable per-task storage allocation using ops.prep_enable().
+ * - Using ops.cpu_release() to handle a higher priority scheduling class taking
+ *   the CPU away.
+ * - Core-sched support.
+ *
+ * This scheduler is primarily for demonstration and testing of sched_ext
+ * features and unlikely to be useful for actual workloads.
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#include <scx/common.bpf.h>
+
+enum consts {
+	ONE_SEC_IN_NS		= 1000000000,
+	SHARED_DSQ		= 0,
+};
+
+char _license[] SEC("license") = "GPL";
+
+const volatile u64 slice_ns = SCX_SLICE_DFL;
+const volatile u32 stall_user_nth;
+const volatile u32 stall_kernel_nth;
+const volatile u32 dsp_inf_loop_after;
+const volatile u32 dsp_batch;
+const volatile bool print_shared_dsq;
+const volatile s32 disallow_tgid;
+const volatile bool suppress_dump;
+
+u32 test_error_cnt;
+
+UEI_DEFINE(uei);
+
+struct qmap {
+	__uint(type, BPF_MAP_TYPE_QUEUE);
+	__uint(max_entries, 4096);
+	__type(value, u32);
+} queue0 SEC(".maps"),
+  queue1 SEC(".maps"),
+  queue2 SEC(".maps"),
+  queue3 SEC(".maps"),
+  queue4 SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY_OF_MAPS);
+	__uint(max_entries, 5);
+	__type(key, int);
+	__array(values, struct qmap);
+} queue_arr SEC(".maps") = {
+	.values = {
+		[0] = &queue0,
+		[1] = &queue1,
+		[2] = &queue2,
+		[3] = &queue3,
+		[4] = &queue4,
+	},
+};
+
+/*
+ * If enabled, CPU performance target is set according to the queue index
+ * according to the following table.
+ */
+static const u32 qidx_to_cpuperf_target[] = {
+	[0] = SCX_CPUPERF_ONE * 0 / 4,
+	[1] = SCX_CPUPERF_ONE * 1 / 4,
+	[2] = SCX_CPUPERF_ONE * 2 / 4,
+	[3] = SCX_CPUPERF_ONE * 3 / 4,
+	[4] = SCX_CPUPERF_ONE * 4 / 4,
+};
+
+/*
+ * Per-queue sequence numbers to implement core-sched ordering.
+ *
+ * Tail seq is assigned to each queued task and incremented. Head seq tracks the
+ * sequence number of the latest dispatched task. The distance between the a
+ * task's seq and the associated queue's head seq is called the queue distance
+ * and used when comparing two tasks for ordering. See qmap_core_sched_before().
+ */
+static u64 core_sched_head_seqs[5];
+static u64 core_sched_tail_seqs[5];
+
+/* Per-task scheduling context */
+struct task_ctx {
+	bool	force_local;	/* Dispatch directly to local_dsq */
+	u64	core_sched_seq;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, struct task_ctx);
+} task_ctx_stor SEC(".maps");
+
+struct cpu_ctx {
+	u64	dsp_idx;	/* dispatch index */
+	u64	dsp_cnt;	/* remaining count */
+	u32	avg_weight;
+	u32	cpuperf_target;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct cpu_ctx);
+} cpu_ctx_stor SEC(".maps");
+
+/* Statistics */
+u64 nr_enqueued, nr_dispatched, nr_reenqueued, nr_dequeued, nr_ddsp_from_enq;
+u64 nr_core_sched_execed;
+u32 cpuperf_min, cpuperf_avg, cpuperf_max;
+u32 cpuperf_target_min, cpuperf_target_avg, cpuperf_target_max;
+
+static s32 pick_direct_dispatch_cpu(struct task_struct *p, s32 prev_cpu)
+{
+	s32 cpu;
+
+	if (p->nr_cpus_allowed == 1 ||
+	    scx_bpf_test_and_clear_cpu_idle(prev_cpu))
+		return prev_cpu;
+
+	cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
+	if (cpu >= 0)
+		return cpu;
+
+	return -1;
+}
+
+s32 BPF_STRUCT_OPS(qmap_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	struct task_ctx *tctx;
+	s32 cpu;
+
+	tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
+	if (!tctx) {
+		scx_bpf_error("task_ctx lookup failed");
+		return -ESRCH;
+	}
+
+	cpu = pick_direct_dispatch_cpu(p, prev_cpu);
+
+	if (cpu >= 0) {
+		tctx->force_local = true;
+		return cpu;
+	} else {
+		return prev_cpu;
+	}
+}
+
+static int weight_to_idx(u32 weight)
+{
+	/* Coarsely map the compound weight to a FIFO. */
+	if (weight <= 25)
+		return 0;
+	else if (weight <= 50)
+		return 1;
+	else if (weight < 200)
+		return 2;
+	else if (weight < 400)
+		return 3;
+	else
+		return 4;
+}
+
+void BPF_STRUCT_OPS(qmap_enqueue, struct task_struct *p, u64 enq_flags)
+{
+	static u32 user_cnt, kernel_cnt;
+	struct task_ctx *tctx;
+	u32 pid = p->pid;
+	int idx = weight_to_idx(p->scx.weight);
+	void *ring;
+	s32 cpu;
+
+	if (p->flags & PF_KTHREAD) {
+		if (stall_kernel_nth && !(++kernel_cnt % stall_kernel_nth))
+			return;
+	} else {
+		if (stall_user_nth && !(++user_cnt % stall_user_nth))
+			return;
+	}
+
+	if (test_error_cnt && !--test_error_cnt)
+		scx_bpf_error("test triggering error");
+
+	tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
+	if (!tctx) {
+		scx_bpf_error("task_ctx lookup failed");
+		return;
+	}
+
+	/*
+	 * All enqueued tasks must have their core_sched_seq updated for correct
+	 * core-sched ordering, which is why %SCX_OPS_ENQ_LAST is specified in
+	 * qmap_ops.flags.
+	 */
+	tctx->core_sched_seq = core_sched_tail_seqs[idx]++;
+
+	/*
+	 * If qmap_select_cpu() is telling us to or this is the last runnable
+	 * task on the CPU, enqueue locally.
+	 */
+	if (tctx->force_local || (enq_flags & SCX_ENQ_LAST)) {
+		tctx->force_local = false;
+		scx_bpf_dispatch(p, SCX_DSQ_LOCAL, slice_ns, enq_flags);
+		return;
+	}
+
+	/* if !WAKEUP, select_cpu() wasn't called, try direct dispatch */
+	if (!(enq_flags & SCX_ENQ_WAKEUP) &&
+	    (cpu = pick_direct_dispatch_cpu(p, scx_bpf_task_cpu(p))) >= 0) {
+		__sync_fetch_and_add(&nr_ddsp_from_enq, 1);
+		scx_bpf_dispatch(p, SCX_DSQ_LOCAL_ON | cpu, slice_ns, enq_flags);
+		return;
+	}
+
+	/*
+	 * If the task was re-enqueued due to the CPU being preempted by a
+	 * higher priority scheduling class, just re-enqueue the task directly
+	 * on the global DSQ. As we want another CPU to pick it up, find and
+	 * kick an idle CPU.
+	 */
+	if (enq_flags & SCX_ENQ_REENQ) {
+		s32 cpu;
+
+		scx_bpf_dispatch(p, SHARED_DSQ, 0, enq_flags);
+		cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
+		if (cpu >= 0)
+			scx_bpf_kick_cpu(cpu, SCX_KICK_IDLE);
+		return;
+	}
+
+	ring = bpf_map_lookup_elem(&queue_arr, &idx);
+	if (!ring) {
+		scx_bpf_error("failed to find ring %d", idx);
+		return;
+	}
+
+	/* Queue on the selected FIFO. If the FIFO overflows, punt to global. */
+	if (bpf_map_push_elem(ring, &pid, 0)) {
+		scx_bpf_dispatch(p, SHARED_DSQ, slice_ns, enq_flags);
+		return;
+	}
+
+	__sync_fetch_and_add(&nr_enqueued, 1);
+}
+
+/*
+ * The BPF queue map doesn't support removal and sched_ext can handle spurious
+ * dispatches. qmap_dequeue() is only used to collect statistics.
+ */
+void BPF_STRUCT_OPS(qmap_dequeue, struct task_struct *p, u64 deq_flags)
+{
+	__sync_fetch_and_add(&nr_dequeued, 1);
+	if (deq_flags & SCX_DEQ_CORE_SCHED_EXEC)
+		__sync_fetch_and_add(&nr_core_sched_execed, 1);
+}
+
+static void update_core_sched_head_seq(struct task_struct *p)
+{
+	struct task_ctx *tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
+	int idx = weight_to_idx(p->scx.weight);
+
+	if (tctx)
+		core_sched_head_seqs[idx] = tctx->core_sched_seq;
+	else
+		scx_bpf_error("task_ctx lookup failed");
+}
+
+void BPF_STRUCT_OPS(qmap_dispatch, s32 cpu, struct task_struct *prev)
+{
+	struct task_struct *p;
+	struct cpu_ctx *cpuc;
+	u32 zero = 0, batch = dsp_batch ?: 1;
+	void *fifo;
+	s32 i, pid;
+
+	if (scx_bpf_consume(SHARED_DSQ))
+		return;
+
+	if (dsp_inf_loop_after && nr_dispatched > dsp_inf_loop_after) {
+		/*
+		 * PID 2 should be kthreadd which should mostly be idle and off
+		 * the scheduler. Let's keep dispatching it to force the kernel
+		 * to call this function over and over again.
+		 */
+		p = bpf_task_from_pid(2);
+		if (p) {
+			scx_bpf_dispatch(p, SCX_DSQ_LOCAL, slice_ns, 0);
+			bpf_task_release(p);
+			return;
+		}
+	}
+
+	if (!(cpuc = bpf_map_lookup_elem(&cpu_ctx_stor, &zero))) {
+		scx_bpf_error("failed to look up cpu_ctx");
+		return;
+	}
+
+	for (i = 0; i < 5; i++) {
+		/* Advance the dispatch cursor and pick the fifo. */
+		if (!cpuc->dsp_cnt) {
+			cpuc->dsp_idx = (cpuc->dsp_idx + 1) % 5;
+			cpuc->dsp_cnt = 1 << cpuc->dsp_idx;
+		}
+
+		fifo = bpf_map_lookup_elem(&queue_arr, &cpuc->dsp_idx);
+		if (!fifo) {
+			scx_bpf_error("failed to find ring %llu", cpuc->dsp_idx);
+			return;
+		}
+
+		/* Dispatch or advance. */
+		bpf_repeat(BPF_MAX_LOOPS) {
+			if (bpf_map_pop_elem(fifo, &pid))
+				break;
+
+			p = bpf_task_from_pid(pid);
+			if (!p)
+				continue;
+
+			update_core_sched_head_seq(p);
+			__sync_fetch_and_add(&nr_dispatched, 1);
+			scx_bpf_dispatch(p, SHARED_DSQ, slice_ns, 0);
+			bpf_task_release(p);
+			batch--;
+			cpuc->dsp_cnt--;
+			if (!batch || !scx_bpf_dispatch_nr_slots()) {
+				scx_bpf_consume(SHARED_DSQ);
+				return;
+			}
+			if (!cpuc->dsp_cnt)
+				break;
+		}
+
+		cpuc->dsp_cnt = 0;
+	}
+}
+
+void BPF_STRUCT_OPS(qmap_tick, struct task_struct *p)
+{
+	struct cpu_ctx *cpuc;
+	u32 zero = 0;
+	int idx;
+
+	if (!(cpuc = bpf_map_lookup_elem(&cpu_ctx_stor, &zero))) {
+		scx_bpf_error("failed to look up cpu_ctx");
+		return;
+	}
+
+	/*
+	 * Use the running avg of weights to select the target cpuperf level.
+	 * This is a demonstration of the cpuperf feature rather than a
+	 * practical strategy to regulate CPU frequency.
+	 */
+	cpuc->avg_weight = cpuc->avg_weight * 3 / 4 + p->scx.weight / 4;
+	idx = weight_to_idx(cpuc->avg_weight);
+	cpuc->cpuperf_target = qidx_to_cpuperf_target[idx];
+
+	scx_bpf_cpuperf_set(scx_bpf_task_cpu(p), cpuc->cpuperf_target);
+}
+
+/*
+ * The distance from the head of the queue scaled by the weight of the queue.
+ * The lower the number, the older the task and the higher the priority.
+ */
+static s64 task_qdist(struct task_struct *p)
+{
+	int idx = weight_to_idx(p->scx.weight);
+	struct task_ctx *tctx;
+	s64 qdist;
+
+	tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
+	if (!tctx) {
+		scx_bpf_error("task_ctx lookup failed");
+		return 0;
+	}
+
+	qdist = tctx->core_sched_seq - core_sched_head_seqs[idx];
+
+	/*
+	 * As queue index increments, the priority doubles. The queue w/ index 3
+	 * is dispatched twice more frequently than 2. Reflect the difference by
+	 * scaling qdists accordingly. Note that the shift amount needs to be
+	 * flipped depending on the sign to avoid flipping priority direction.
+	 */
+	if (qdist >= 0)
+		return qdist << (4 - idx);
+	else
+		return qdist << idx;
+}
+
+/*
+ * This is called to determine the task ordering when core-sched is picking
+ * tasks to execute on SMT siblings and should encode about the same ordering as
+ * the regular scheduling path. Use the priority-scaled distances from the head
+ * of the queues to compare the two tasks which should be consistent with the
+ * dispatch path behavior.
+ */
+bool BPF_STRUCT_OPS(qmap_core_sched_before,
+		    struct task_struct *a, struct task_struct *b)
+{
+	return task_qdist(a) > task_qdist(b);
+}
+
+void BPF_STRUCT_OPS(qmap_cpu_release, s32 cpu, struct scx_cpu_release_args *args)
+{
+	u32 cnt;
+
+	/*
+	 * Called when @cpu is taken by a higher priority scheduling class. This
+	 * makes @cpu no longer available for executing sched_ext tasks. As we
+	 * don't want the tasks in @cpu's local dsq to sit there until @cpu
+	 * becomes available again, re-enqueue them into the global dsq. See
+	 * %SCX_ENQ_REENQ handling in qmap_enqueue().
+	 */
+	cnt = scx_bpf_reenqueue_local();
+	if (cnt)
+		__sync_fetch_and_add(&nr_reenqueued, cnt);
+}
+
+s32 BPF_STRUCT_OPS(qmap_init_task, struct task_struct *p,
+		   struct scx_init_task_args *args)
+{
+	if (p->tgid == disallow_tgid)
+		p->scx.disallow = true;
+
+	/*
+	 * @p is new. Let's ensure that its task_ctx is available. We can sleep
+	 * in this function and the following will automatically use GFP_KERNEL.
+	 */
+	if (bpf_task_storage_get(&task_ctx_stor, p, 0,
+				 BPF_LOCAL_STORAGE_GET_F_CREATE))
+		return 0;
+	else
+		return -ENOMEM;
+}
+
+void BPF_STRUCT_OPS(qmap_dump, struct scx_dump_ctx *dctx)
+{
+	s32 i, pid;
+
+	if (suppress_dump)
+		return;
+
+	bpf_for(i, 0, 5) {
+		void *fifo;
+
+		if (!(fifo = bpf_map_lookup_elem(&queue_arr, &i)))
+			return;
+
+		scx_bpf_dump("QMAP FIFO[%d]:", i);
+		bpf_repeat(4096) {
+			if (bpf_map_pop_elem(fifo, &pid))
+				break;
+			scx_bpf_dump(" %d", pid);
+		}
+		scx_bpf_dump("\n");
+	}
+}
+
+void BPF_STRUCT_OPS(qmap_dump_cpu, struct scx_dump_ctx *dctx, s32 cpu, bool idle)
+{
+	u32 zero = 0;
+	struct cpu_ctx *cpuc;
+
+	if (suppress_dump || idle)
+		return;
+	if (!(cpuc = bpf_map_lookup_percpu_elem(&cpu_ctx_stor, &zero, cpu)))
+		return;
+
+	scx_bpf_dump("QMAP: dsp_idx=%llu dsp_cnt=%llu avg_weight=%u cpuperf_target=%u",
+		     cpuc->dsp_idx, cpuc->dsp_cnt, cpuc->avg_weight,
+		     cpuc->cpuperf_target);
+}
+
+void BPF_STRUCT_OPS(qmap_dump_task, struct scx_dump_ctx *dctx, struct task_struct *p)
+{
+	struct task_ctx *taskc;
+
+	if (suppress_dump)
+		return;
+	if (!(taskc = bpf_task_storage_get(&task_ctx_stor, p, 0, 0)))
+		return;
+
+	scx_bpf_dump("QMAP: force_local=%d core_sched_seq=%llu",
+		     taskc->force_local, taskc->core_sched_seq);
+}
+
+/*
+ * Print out the online and possible CPU map using bpf_printk() as a
+ * demonstration of using the cpumask kfuncs and ops.cpu_on/offline().
+ */
+static void print_cpus(void)
+{
+	const struct cpumask *possible, *online;
+	s32 cpu;
+	char buf[128] = "", *p;
+	int idx;
+
+	possible = scx_bpf_get_possible_cpumask();
+	online = scx_bpf_get_online_cpumask();
+
+	idx = 0;
+	bpf_for(cpu, 0, scx_bpf_nr_cpu_ids()) {
+		if (!(p = MEMBER_VPTR(buf, [idx++])))
+			break;
+		if (bpf_cpumask_test_cpu(cpu, online))
+			*p++ = 'O';
+		else if (bpf_cpumask_test_cpu(cpu, possible))
+			*p++ = 'X';
+		else
+			*p++ = ' ';
+
+		if ((cpu & 7) == 7) {
+			if (!(p = MEMBER_VPTR(buf, [idx++])))
+				break;
+			*p++ = '|';
+		}
+	}
+	buf[sizeof(buf) - 1] = '\0';
+
+	scx_bpf_put_cpumask(online);
+	scx_bpf_put_cpumask(possible);
+
+	bpf_printk("CPUS: |%s", buf);
+}
+
+void BPF_STRUCT_OPS(qmap_cpu_online, s32 cpu)
+{
+	bpf_printk("CPU %d coming online", cpu);
+	/* @cpu is already online at this point */
+	print_cpus();
+}
+
+void BPF_STRUCT_OPS(qmap_cpu_offline, s32 cpu)
+{
+	bpf_printk("CPU %d going offline", cpu);
+	/* @cpu is still online at this point */
+	print_cpus();
+}
+
+struct monitor_timer {
+	struct bpf_timer timer;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct monitor_timer);
+} monitor_timer SEC(".maps");
+
+/*
+ * Print out the min, avg and max performance levels of CPUs every second to
+ * demonstrate the cpuperf interface.
+ */
+static void monitor_cpuperf(void)
+{
+	u32 zero = 0, nr_cpu_ids;
+	u64 cap_sum = 0, cur_sum = 0, cur_min = SCX_CPUPERF_ONE, cur_max = 0;
+	u64 target_sum = 0, target_min = SCX_CPUPERF_ONE, target_max = 0;
+	const struct cpumask *online;
+	int i, nr_online_cpus = 0;
+
+	nr_cpu_ids = scx_bpf_nr_cpu_ids();
+	online = scx_bpf_get_online_cpumask();
+
+	bpf_for(i, 0, nr_cpu_ids) {
+		struct cpu_ctx *cpuc;
+		u32 cap, cur;
+
+		if (!bpf_cpumask_test_cpu(i, online))
+			continue;
+		nr_online_cpus++;
+
+		/* collect the capacity and current cpuperf */
+		cap = scx_bpf_cpuperf_cap(i);
+		cur = scx_bpf_cpuperf_cur(i);
+
+		cur_min = cur < cur_min ? cur : cur_min;
+		cur_max = cur > cur_max ? cur : cur_max;
+
+		/*
+		 * $cur is relative to $cap. Scale it down accordingly so that
+		 * it's in the same scale as other CPUs and $cur_sum/$cap_sum
+		 * makes sense.
+		 */
+		cur_sum += cur * cap / SCX_CPUPERF_ONE;
+		cap_sum += cap;
+
+		if (!(cpuc = bpf_map_lookup_percpu_elem(&cpu_ctx_stor, &zero, i))) {
+			scx_bpf_error("failed to look up cpu_ctx");
+			goto out;
+		}
+
+		/* collect target */
+		cur = cpuc->cpuperf_target;
+		target_sum += cur;
+		target_min = cur < target_min ? cur : target_min;
+		target_max = cur > target_max ? cur : target_max;
+	}
+
+	cpuperf_min = cur_min;
+	cpuperf_avg = cur_sum * SCX_CPUPERF_ONE / cap_sum;
+	cpuperf_max = cur_max;
+
+	cpuperf_target_min = target_min;
+	cpuperf_target_avg = target_sum / nr_online_cpus;
+	cpuperf_target_max = target_max;
+out:
+	scx_bpf_put_cpumask(online);
+}
+
+/*
+ * Dump the currently queued tasks in the shared DSQ to demonstrate the usage of
+ * scx_bpf_dsq_nr_queued() and DSQ iterator. Raise the dispatch batch count to
+ * see meaningful dumps in the trace pipe.
+ */
+static void dump_shared_dsq(void)
+{
+	struct task_struct *p;
+	s32 nr;
+
+	if (!(nr = scx_bpf_dsq_nr_queued(SHARED_DSQ)))
+		return;
+
+	bpf_printk("Dumping %d tasks in SHARED_DSQ in reverse order", nr);
+
+	bpf_rcu_read_lock();
+	bpf_for_each(scx_dsq, p, SHARED_DSQ, SCX_DSQ_ITER_REV)
+		bpf_printk("%s[%d]", p->comm, p->pid);
+	bpf_rcu_read_unlock();
+}
+
+static int monitor_timerfn(void *map, int *key, struct bpf_timer *timer)
+{
+	monitor_cpuperf();
+
+	if (print_shared_dsq)
+		dump_shared_dsq();
+
+	bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
+	return 0;
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(qmap_init)
+{
+	u32 key = 0;
+	struct bpf_timer *timer;
+	s32 ret;
+
+	print_cpus();
+
+	ret = scx_bpf_create_dsq(SHARED_DSQ, -1);
+	if (ret)
+		return ret;
+
+	timer = bpf_map_lookup_elem(&monitor_timer, &key);
+	if (!timer)
+		return -ESRCH;
+
+	bpf_timer_init(timer, &monitor_timer, CLOCK_MONOTONIC);
+	bpf_timer_set_callback(timer, monitor_timerfn);
+
+	return bpf_timer_start(timer, ONE_SEC_IN_NS, 0);
+}
+
+void BPF_STRUCT_OPS(qmap_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SCX_OPS_DEFINE(qmap_ops,
+	       .select_cpu		= (void *)qmap_select_cpu,
+	       .enqueue			= (void *)qmap_enqueue,
+	       .dequeue			= (void *)qmap_dequeue,
+	       .dispatch		= (void *)qmap_dispatch,
+	       .tick			= (void *)qmap_tick,
+	       .core_sched_before	= (void *)qmap_core_sched_before,
+	       .cpu_release		= (void *)qmap_cpu_release,
+	       .init_task		= (void *)qmap_init_task,
+	       .dump			= (void *)qmap_dump,
+	       .dump_cpu		= (void *)qmap_dump_cpu,
+	       .dump_task		= (void *)qmap_dump_task,
+	       .cpu_online		= (void *)qmap_cpu_online,
+	       .cpu_offline		= (void *)qmap_cpu_offline,
+	       .init			= (void *)qmap_init,
+	       .exit			= (void *)qmap_exit,
+	       .flags			= SCX_OPS_ENQ_LAST,
+	       .timeout_ms		= 5000U,
+	       .name			= "qmap");
diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
new file mode 100644
index 000000000000..c9ca30d62b2b
--- /dev/null
+++ b/tools/sched_ext/scx_qmap.c
@@ -0,0 +1,144 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <inttypes.h>
+#include <signal.h>
+#include <libgen.h>
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include "scx_qmap.bpf.skel.h"
+
+const char help_fmt[] =
+"A simple five-level FIFO queue sched_ext scheduler.\n"
+"\n"
+"See the top-level comment in .bpf.c for more details.\n"
+"\n"
+"Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-l COUNT] [-b COUNT]\n"
+"       [-P] [-d PID] [-D LEN] [-p] [-v]\n"
+"\n"
+"  -s SLICE_US   Override slice duration\n"
+"  -e COUNT      Trigger scx_bpf_error() after COUNT enqueues\n"
+"  -t COUNT      Stall every COUNT'th user thread\n"
+"  -T COUNT      Stall every COUNT'th kernel thread\n"
+"  -l COUNT      Trigger dispatch infinite looping after COUNT dispatches\n"
+"  -b COUNT      Dispatch upto COUNT tasks together\n"
+"  -P            Print out DSQ content to trace_pipe every second, use with -b\n"
+"  -d PID        Disallow a process from switching into SCHED_EXT (-1 for self)\n"
+"  -D LEN        Set scx_exit_info.dump buffer length\n"
+"  -S            Suppress qmap-specific debug dump\n"
+"  -p            Switch only tasks on SCHED_EXT policy instead of all\n"
+"  -v            Print libbpf debug messages\n"
+"  -h            Display this help and exit\n";
+
+static bool verbose;
+static volatile int exit_req;
+
+static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
+{
+	if (level == LIBBPF_DEBUG && !verbose)
+		return 0;
+	return vfprintf(stderr, format, args);
+}
+
+static void sigint_handler(int dummy)
+{
+	exit_req = 1;
+}
+
+int main(int argc, char **argv)
+{
+	struct scx_qmap *skel;
+	struct bpf_link *link;
+	int opt;
+
+	libbpf_set_print(libbpf_print_fn);
+	signal(SIGINT, sigint_handler);
+	signal(SIGTERM, sigint_handler);
+
+	skel = SCX_OPS_OPEN(qmap_ops, scx_qmap);
+
+	while ((opt = getopt(argc, argv, "s:e:t:T:l:b:Pd:D:Spvh")) != -1) {
+		switch (opt) {
+		case 's':
+			skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000;
+			break;
+		case 'e':
+			skel->bss->test_error_cnt = strtoul(optarg, NULL, 0);
+			break;
+		case 't':
+			skel->rodata->stall_user_nth = strtoul(optarg, NULL, 0);
+			break;
+		case 'T':
+			skel->rodata->stall_kernel_nth = strtoul(optarg, NULL, 0);
+			break;
+		case 'l':
+			skel->rodata->dsp_inf_loop_after = strtoul(optarg, NULL, 0);
+			break;
+		case 'b':
+			skel->rodata->dsp_batch = strtoul(optarg, NULL, 0);
+			break;
+		case 'P':
+			skel->rodata->print_shared_dsq = true;
+			break;
+		case 'd':
+			skel->rodata->disallow_tgid = strtol(optarg, NULL, 0);
+			if (skel->rodata->disallow_tgid < 0)
+				skel->rodata->disallow_tgid = getpid();
+			break;
+		case 'D':
+			skel->struct_ops.qmap_ops->exit_dump_len = strtoul(optarg, NULL, 0);
+			break;
+		case 'S':
+			skel->rodata->suppress_dump = true;
+			break;
+		case 'p':
+			skel->struct_ops.qmap_ops->flags |= SCX_OPS_SWITCH_PARTIAL;
+			break;
+		case 'v':
+			verbose = true;
+			break;
+		default:
+			fprintf(stderr, help_fmt, basename(argv[0]));
+			return opt != 'h';
+		}
+	}
+
+	SCX_OPS_LOAD(skel, qmap_ops, scx_qmap, uei);
+	link = SCX_OPS_ATTACH(skel, qmap_ops, scx_qmap);
+
+	while (!exit_req && !UEI_EXITED(skel, uei)) {
+		long nr_enqueued = skel->bss->nr_enqueued;
+		long nr_dispatched = skel->bss->nr_dispatched;
+
+		printf("stats  : enq=%lu dsp=%lu delta=%ld reenq=%"PRIu64" deq=%"PRIu64" core=%"PRIu64" enq_ddsp=%"PRIu64"\n",
+		       nr_enqueued, nr_dispatched, nr_enqueued - nr_dispatched,
+		       skel->bss->nr_reenqueued, skel->bss->nr_dequeued,
+		       skel->bss->nr_core_sched_execed,
+		       skel->bss->nr_ddsp_from_enq);
+		if (__COMPAT_has_ksym("scx_bpf_cpuperf_cur"))
+			printf("cpuperf: cur min/avg/max=%u/%u/%u target min/avg/max=%u/%u/%u\n",
+			       skel->bss->cpuperf_min,
+			       skel->bss->cpuperf_avg,
+			       skel->bss->cpuperf_max,
+			       skel->bss->cpuperf_target_min,
+			       skel->bss->cpuperf_target_avg,
+			       skel->bss->cpuperf_target_max);
+		fflush(stdout);
+		sleep(1);
+	}
+
+	bpf_link__destroy(link);
+	UEI_REPORT(skel, uei);
+	scx_qmap__destroy(skel);
+	/*
+	 * scx_qmap implements ops.cpu_on/offline() and doesn't need to restart
+	 * on CPU hotplug events.
+	 */
+	return 0;
+}
diff --git a/tools/sched_ext/scx_show_state.py b/tools/sched_ext/scx_show_state.py
new file mode 100644
index 000000000000..d457d2a74e1e
--- /dev/null
+++ b/tools/sched_ext/scx_show_state.py
@@ -0,0 +1,39 @@
+#!/usr/bin/env drgn
+#
+# Copyright (C) 2024 Tejun Heo <tj@kernel.org>
+# Copyright (C) 2024 Meta Platforms, Inc. and affiliates.
+
+desc = """
+This is a drgn script to show the current sched_ext state.
+For more info on drgn, visit https://github.com/osandov/drgn.
+"""
+
+import drgn
+import sys
+
+def err(s):
+    print(s, file=sys.stderr, flush=True)
+    sys.exit(1)
+
+def read_int(name):
+    return int(prog[name].value_())
+
+def read_atomic(name):
+    return prog[name].counter.value_()
+
+def read_static_key(name):
+    return prog[name].key.enabled.counter.value_()
+
+def ops_state_str(state):
+    return prog['scx_ops_enable_state_str'][state].string_().decode()
+
+ops = prog['scx_ops']
+enable_state = read_atomic("scx_ops_enable_state_var")
+
+print(f'ops           : {ops.name.string_().decode()}')
+print(f'enabled       : {read_static_key("__scx_ops_enabled")}')
+print(f'switching_all : {read_int("scx_switching_all")}')
+print(f'switched_all  : {read_static_key("__scx_switched_all")}')
+print(f'enable_state  : {ops_state_str(enable_state)} ({enable_state})')
+print(f'bypass_depth  : {read_atomic("scx_ops_bypass_depth")}')
+print(f'nr_rejected   : {read_atomic("scx_nr_rejected")}')
diff --git a/tools/sched_ext/scx_simple.bpf.c b/tools/sched_ext/scx_simple.bpf.c
new file mode 100644
index 000000000000..ed7e8d535fc5
--- /dev/null
+++ b/tools/sched_ext/scx_simple.bpf.c
@@ -0,0 +1,156 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A simple scheduler.
+ *
+ * By default, it operates as a simple global weighted vtime scheduler and can
+ * be switched to FIFO scheduling. It also demonstrates the following niceties.
+ *
+ * - Statistics tracking how many tasks are queued to local and global dsq's.
+ * - Termination notification for userspace.
+ *
+ * While very simple, this scheduler should work reasonably well on CPUs with a
+ * uniform L3 cache topology. While preemption is not implemented, the fact that
+ * the scheduling queue is shared across all CPUs means that whatever is at the
+ * front of the queue is likely to be executed fairly quickly given enough
+ * number of CPUs. The FIFO scheduling mode may be beneficial to some workloads
+ * but comes with the usual problems with FIFO scheduling where saturating
+ * threads can easily drown out interactive ones.
+ *
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+const volatile bool fifo_sched;
+
+static u64 vtime_now;
+UEI_DEFINE(uei);
+
+/*
+ * Built-in DSQs such as SCX_DSQ_GLOBAL cannot be used as priority queues
+ * (meaning, cannot be dispatched to with scx_bpf_dispatch_vtime()). We
+ * therefore create a separate DSQ with ID 0 that we dispatch to and consume
+ * from. If scx_simple only supported global FIFO scheduling, then we could
+ * just use SCX_DSQ_GLOBAL.
+ */
+#define SHARED_DSQ 0
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+	__uint(key_size, sizeof(u32));
+	__uint(value_size, sizeof(u64));
+	__uint(max_entries, 2);			/* [local, global] */
+} stats SEC(".maps");
+
+static void stat_inc(u32 idx)
+{
+	u64 *cnt_p = bpf_map_lookup_elem(&stats, &idx);
+	if (cnt_p)
+		(*cnt_p)++;
+}
+
+static inline bool vtime_before(u64 a, u64 b)
+{
+	return (s64)(a - b) < 0;
+}
+
+s32 BPF_STRUCT_OPS(simple_select_cpu, struct task_struct *p, s32 prev_cpu, u64 wake_flags)
+{
+	bool is_idle = false;
+	s32 cpu;
+
+	cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, wake_flags, &is_idle);
+	if (is_idle) {
+		stat_inc(0);	/* count local queueing */
+		scx_bpf_dispatch(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, 0);
+	}
+
+	return cpu;
+}
+
+void BPF_STRUCT_OPS(simple_enqueue, struct task_struct *p, u64 enq_flags)
+{
+	stat_inc(1);	/* count global queueing */
+
+	if (fifo_sched) {
+		scx_bpf_dispatch(p, SHARED_DSQ, SCX_SLICE_DFL, enq_flags);
+	} else {
+		u64 vtime = p->scx.dsq_vtime;
+
+		/*
+		 * Limit the amount of budget that an idling task can accumulate
+		 * to one slice.
+		 */
+		if (vtime_before(vtime, vtime_now - SCX_SLICE_DFL))
+			vtime = vtime_now - SCX_SLICE_DFL;
+
+		scx_bpf_dispatch_vtime(p, SHARED_DSQ, SCX_SLICE_DFL, vtime,
+				       enq_flags);
+	}
+}
+
+void BPF_STRUCT_OPS(simple_dispatch, s32 cpu, struct task_struct *prev)
+{
+	scx_bpf_consume(SHARED_DSQ);
+}
+
+void BPF_STRUCT_OPS(simple_running, struct task_struct *p)
+{
+	if (fifo_sched)
+		return;
+
+	/*
+	 * Global vtime always progresses forward as tasks start executing. The
+	 * test and update can be performed concurrently from multiple CPUs and
+	 * thus racy. Any error should be contained and temporary. Let's just
+	 * live with it.
+	 */
+	if (vtime_before(vtime_now, p->scx.dsq_vtime))
+		vtime_now = p->scx.dsq_vtime;
+}
+
+void BPF_STRUCT_OPS(simple_stopping, struct task_struct *p, bool runnable)
+{
+	if (fifo_sched)
+		return;
+
+	/*
+	 * Scale the execution time by the inverse of the weight and charge.
+	 *
+	 * Note that the default yield implementation yields by setting
+	 * @p->scx.slice to zero and the following would treat the yielding task
+	 * as if it has consumed all its slice. If this penalizes yielding tasks
+	 * too much, determine the execution time by taking explicit timestamps
+	 * instead of depending on @p->scx.slice.
+	 */
+	p->scx.dsq_vtime += (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+}
+
+void BPF_STRUCT_OPS(simple_enable, struct task_struct *p)
+{
+	p->scx.dsq_vtime = vtime_now;
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(simple_init)
+{
+	return scx_bpf_create_dsq(SHARED_DSQ, -1);
+}
+
+void BPF_STRUCT_OPS(simple_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SCX_OPS_DEFINE(simple_ops,
+	       .select_cpu		= (void *)simple_select_cpu,
+	       .enqueue			= (void *)simple_enqueue,
+	       .dispatch		= (void *)simple_dispatch,
+	       .running			= (void *)simple_running,
+	       .stopping		= (void *)simple_stopping,
+	       .enable			= (void *)simple_enable,
+	       .init			= (void *)simple_init,
+	       .exit			= (void *)simple_exit,
+	       .name			= "simple");
diff --git a/tools/sched_ext/scx_simple.c b/tools/sched_ext/scx_simple.c
new file mode 100644
index 000000000000..76d83199545c
--- /dev/null
+++ b/tools/sched_ext/scx_simple.c
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2022 David Vernet <dvernet@meta.com>
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <signal.h>
+#include <libgen.h>
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include "scx_simple.bpf.skel.h"
+
+const char help_fmt[] =
+"A simple sched_ext scheduler.\n"
+"\n"
+"See the top-level comment in .bpf.c for more details.\n"
+"\n"
+"Usage: %s [-f] [-v]\n"
+"\n"
+"  -f            Use FIFO scheduling instead of weighted vtime scheduling\n"
+"  -v            Print libbpf debug messages\n"
+"  -h            Display this help and exit\n";
+
+static bool verbose;
+static volatile int exit_req;
+
+static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
+{
+	if (level == LIBBPF_DEBUG && !verbose)
+		return 0;
+	return vfprintf(stderr, format, args);
+}
+
+static void sigint_handler(int simple)
+{
+	exit_req = 1;
+}
+
+static void read_stats(struct scx_simple *skel, __u64 *stats)
+{
+	int nr_cpus = libbpf_num_possible_cpus();
+	__u64 cnts[2][nr_cpus];
+	__u32 idx;
+
+	memset(stats, 0, sizeof(stats[0]) * 2);
+
+	for (idx = 0; idx < 2; idx++) {
+		int ret, cpu;
+
+		ret = bpf_map_lookup_elem(bpf_map__fd(skel->maps.stats),
+					  &idx, cnts[idx]);
+		if (ret < 0)
+			continue;
+		for (cpu = 0; cpu < nr_cpus; cpu++)
+			stats[idx] += cnts[idx][cpu];
+	}
+}
+
+int main(int argc, char **argv)
+{
+	struct scx_simple *skel;
+	struct bpf_link *link;
+	__u32 opt;
+	__u64 ecode;
+
+	libbpf_set_print(libbpf_print_fn);
+	signal(SIGINT, sigint_handler);
+	signal(SIGTERM, sigint_handler);
+restart:
+	skel = SCX_OPS_OPEN(simple_ops, scx_simple);
+
+	while ((opt = getopt(argc, argv, "fvh")) != -1) {
+		switch (opt) {
+		case 'f':
+			skel->rodata->fifo_sched = true;
+			break;
+		case 'v':
+			verbose = true;
+			break;
+		default:
+			fprintf(stderr, help_fmt, basename(argv[0]));
+			return opt != 'h';
+		}
+	}
+
+	SCX_OPS_LOAD(skel, simple_ops, scx_simple, uei);
+	link = SCX_OPS_ATTACH(skel, simple_ops, scx_simple);
+
+	while (!exit_req && !UEI_EXITED(skel, uei)) {
+		__u64 stats[2];
+
+		read_stats(skel, stats);
+		printf("local=%llu global=%llu\n", stats[0], stats[1]);
+		fflush(stdout);
+		sleep(1);
+	}
+
+	bpf_link__destroy(link);
+	ecode = UEI_REPORT(skel, uei);
+	scx_simple__destroy(skel);
+
+	if (UEI_ECODE_RESTART(ecode))
+		goto restart;
+	return 0;
+}
diff --git a/tools/testing/selftests/sched_ext/.gitignore b/tools/testing/selftests/sched_ext/.gitignore
new file mode 100644
index 000000000000..ae5491a114c0
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/.gitignore
@@ -0,0 +1,6 @@
+*
+!*.c
+!*.h
+!Makefile
+!.gitignore
+!config
diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
new file mode 100644
index 000000000000..0754a2c110a1
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -0,0 +1,218 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
+include ../../../build/Build.include
+include ../../../scripts/Makefile.arch
+include ../../../scripts/Makefile.include
+include ../lib.mk
+
+ifneq ($(LLVM),)
+ifneq ($(filter %/,$(LLVM)),)
+LLVM_PREFIX := $(LLVM)
+else ifneq ($(filter -%,$(LLVM)),)
+LLVM_SUFFIX := $(LLVM)
+endif
+
+CC := $(LLVM_PREFIX)clang$(LLVM_SUFFIX) $(CLANG_FLAGS) -fintegrated-as
+else
+CC := gcc
+endif # LLVM
+
+ifneq ($(CROSS_COMPILE),)
+$(error CROSS_COMPILE not supported for scx selftests)
+endif # CROSS_COMPILE
+
+CURDIR := $(abspath .)
+REPOROOT := $(abspath ../../../..)
+TOOLSDIR := $(REPOROOT)/tools
+LIBDIR := $(TOOLSDIR)/lib
+BPFDIR := $(LIBDIR)/bpf
+TOOLSINCDIR := $(TOOLSDIR)/include
+BPFTOOLDIR := $(TOOLSDIR)/bpf/bpftool
+APIDIR := $(TOOLSINCDIR)/uapi
+GENDIR := $(REPOROOT)/include/generated
+GENHDR := $(GENDIR)/autoconf.h
+SCXTOOLSDIR := $(TOOLSDIR)/sched_ext
+SCXTOOLSINCDIR := $(TOOLSDIR)/sched_ext/include
+
+OUTPUT_DIR := $(CURDIR)/build
+OBJ_DIR := $(OUTPUT_DIR)/obj
+INCLUDE_DIR := $(OUTPUT_DIR)/include
+BPFOBJ_DIR := $(OBJ_DIR)/libbpf
+SCXOBJ_DIR := $(OBJ_DIR)/sched_ext
+BPFOBJ := $(BPFOBJ_DIR)/libbpf.a
+LIBBPF_OUTPUT := $(OBJ_DIR)/libbpf/libbpf.a
+DEFAULT_BPFTOOL := $(OUTPUT_DIR)/sbin/bpftool
+HOST_BUILD_DIR := $(OBJ_DIR)
+HOST_OUTPUT_DIR := $(OUTPUT_DIR)
+
+VMLINUX_BTF_PATHS ?= ../../../../vmlinux					\
+		     /sys/kernel/btf/vmlinux					\
+		     /boot/vmlinux-$(shell uname -r)
+VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
+ifeq ($(VMLINUX_BTF),)
+$(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)")
+endif
+
+BPFTOOL ?= $(DEFAULT_BPFTOOL)
+
+ifneq ($(wildcard $(GENHDR)),)
+  GENFLAGS := -DHAVE_GENHDR
+endif
+
+CFLAGS += -g -O2 -rdynamic -pthread -Wall -Werror $(GENFLAGS)			\
+	  -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)				\
+	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(CURDIR)/include -I$(SCXTOOLSINCDIR)
+
+# Silence some warnings when compiled with clang
+ifneq ($(LLVM),)
+CFLAGS += -Wno-unused-command-line-argument
+endif
+
+LDFLAGS = -lelf -lz -lpthread -lzstd
+
+IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null |				\
+			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
+
+# Get Clang's default includes on this system, as opposed to those seen by
+# '-target bpf'. This fixes "missing" files on some architectures/distros,
+# such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
+#
+# Use '-idirafter': Don't interfere with include mechanics except where the
+# build would have failed anyways.
+define get_sys_includes
+$(shell $(1) -v -E - </dev/null 2>&1 \
+	| sed -n '/<...> search starts here:/,/End of search list./{ s| \(/.*\)|-idirafter \1|p }') \
+$(shell $(1) -dM -E - </dev/null | grep '__riscv_xlen ' | awk '{printf("-D__riscv_xlen=%d -D__BITS_PER_LONG=%d", $$3, $$3)}')
+endef
+
+BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH)					\
+	     $(if $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)		\
+	     -I$(CURDIR)/include -I$(CURDIR)/include/bpf-compat			\
+	     -I$(INCLUDE_DIR) -I$(APIDIR) -I$(SCXTOOLSINCDIR)			\
+	     -I$(REPOROOT)/include						\
+	     $(call get_sys_includes,$(CLANG))					\
+	     -Wall -Wno-compare-distinct-pointer-types				\
+	     -Wno-incompatible-function-pointer-types				\
+	     -O2 -mcpu=v3
+
+# sort removes libbpf duplicates when not cross-building
+MAKE_DIRS := $(sort $(OBJ_DIR)/libbpf $(OBJ_DIR)/libbpf				\
+	       $(OBJ_DIR)/bpftool $(OBJ_DIR)/resolve_btfids			\
+	       $(INCLUDE_DIR) $(SCXOBJ_DIR))
+
+$(MAKE_DIRS):
+	$(call msg,MKDIR,,$@)
+	$(Q)mkdir -p $@
+
+$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)			\
+	   $(APIDIR)/linux/bpf.h						\
+	   | $(OBJ_DIR)/libbpf
+	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(OBJ_DIR)/libbpf/	\
+		    EXTRA_CFLAGS='-g -O0 -fPIC'					\
+		    DESTDIR=$(OUTPUT_DIR) prefix= all install_headers
+
+$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile)	\
+		    $(LIBBPF_OUTPUT) | $(OBJ_DIR)/bpftool
+	$(Q)$(MAKE) $(submake_extras)  -C $(BPFTOOLDIR)				\
+		    ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD)		\
+		    EXTRA_CFLAGS='-g -O0'					\
+		    OUTPUT=$(OBJ_DIR)/bpftool/					\
+		    LIBBPF_OUTPUT=$(OBJ_DIR)/libbpf/				\
+		    LIBBPF_DESTDIR=$(OUTPUT_DIR)/				\
+		    prefix= DESTDIR=$(OUTPUT_DIR)/ install-bin
+
+$(INCLUDE_DIR)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR)
+ifeq ($(VMLINUX_H),)
+	$(call msg,GEN,,$@)
+	$(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@
+else
+	$(call msg,CP,,$@)
+	$(Q)cp "$(VMLINUX_H)" $@
+endif
+
+$(SCXOBJ_DIR)/%.bpf.o: %.bpf.c $(INCLUDE_DIR)/vmlinux.h	| $(BPFOBJ) $(SCXOBJ_DIR)
+	$(call msg,CLNG-BPF,,$(notdir $@))
+	$(Q)$(CLANG) $(BPF_CFLAGS) -target bpf -c $< -o $@
+
+$(INCLUDE_DIR)/%.bpf.skel.h: $(SCXOBJ_DIR)/%.bpf.o $(INCLUDE_DIR)/vmlinux.h $(BPFTOOL) | $(INCLUDE_DIR)
+	$(eval sched=$(notdir $@))
+	$(call msg,GEN-SKEL,,$(sched))
+	$(Q)$(BPFTOOL) gen object $(<:.o=.linked1.o) $<
+	$(Q)$(BPFTOOL) gen object $(<:.o=.linked2.o) $(<:.o=.linked1.o)
+	$(Q)$(BPFTOOL) gen object $(<:.o=.linked3.o) $(<:.o=.linked2.o)
+	$(Q)diff $(<:.o=.linked2.o) $(<:.o=.linked3.o)
+	$(Q)$(BPFTOOL) gen skeleton $(<:.o=.linked3.o) name $(subst .bpf.skel.h,,$(sched)) > $@
+	$(Q)$(BPFTOOL) gen subskeleton $(<:.o=.linked3.o) name $(subst .bpf.skel.h,,$(sched)) > $(@:.skel.h=.subskel.h)
+
+################
+# C schedulers #
+################
+
+override define CLEAN
+	rm -rf $(OUTPUT_DIR)
+	rm -f *.o *.bpf.o *.bpf.skel.h *.bpf.subskel.h
+	rm -f $(TEST_GEN_PROGS)
+	rm -f runner
+endef
+
+# Every testcase takes all of the BPF progs are dependencies by default. This
+# allows testcases to load any BPF scheduler, which is useful for testcases
+# that don't need their own prog to run their test.
+all_test_bpfprogs := $(foreach prog,$(wildcard *.bpf.c),$(INCLUDE_DIR)/$(patsubst %.c,%.skel.h,$(prog)))
+
+auto-test-targets :=			\
+	create_dsq			\
+	enq_last_no_enq_fails		\
+	enq_select_cpu_fails		\
+	ddsp_bogus_dsq_fail		\
+	ddsp_vtimelocal_fail		\
+	dsp_local_on			\
+	exit				\
+	hotplug				\
+	init_enable_count		\
+	maximal				\
+	maybe_null			\
+	minimal				\
+	prog_run			\
+	reload_loop			\
+	select_cpu_dfl			\
+	select_cpu_dfl_nodispatch	\
+	select_cpu_dispatch		\
+	select_cpu_dispatch_bad_dsq	\
+	select_cpu_dispatch_dbl_dsp	\
+	select_cpu_vtime		\
+	test_example			\
+
+testcase-targets := $(addsuffix .o,$(addprefix $(SCXOBJ_DIR)/,$(auto-test-targets)))
+
+$(SCXOBJ_DIR)/runner.o: runner.c | $(SCXOBJ_DIR)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+# Create all of the test targets object files, whose testcase objects will be
+# registered into the runner in ELF constructors.
+#
+# Note that we must do double expansion here in order to support conditionally
+# compiling BPF object files only if one is present, as the wildcard Make
+# function doesn't support using implicit rules otherwise.
+$(testcase-targets): $(SCXOBJ_DIR)/%.o: %.c $(SCXOBJ_DIR)/runner.o $(all_test_bpfprogs) | $(SCXOBJ_DIR)
+	$(eval test=$(patsubst %.o,%.c,$(notdir $@)))
+	$(CC) $(CFLAGS) -c $< -o $@ $(SCXOBJ_DIR)/runner.o
+
+$(SCXOBJ_DIR)/util.o: util.c | $(SCXOBJ_DIR)
+	$(CC) $(CFLAGS) -c $< -o $@
+
+runner: $(SCXOBJ_DIR)/runner.o $(SCXOBJ_DIR)/util.o $(BPFOBJ) $(testcase-targets)
+	@echo "$(testcase-targets)"
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+TEST_GEN_PROGS := runner
+
+all: runner
+
+.PHONY: all clean help
+
+.DEFAULT_GOAL := all
+
+.DELETE_ON_ERROR:
+
+.SECONDARY:
diff --git a/tools/testing/selftests/sched_ext/config b/tools/testing/selftests/sched_ext/config
new file mode 100644
index 000000000000..0de9b4ee249d
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/config
@@ -0,0 +1,9 @@
+CONFIG_SCHED_DEBUG=y
+CONFIG_SCHED_CLASS_EXT=y
+CONFIG_CGROUPS=y
+CONFIG_CGROUP_SCHED=y
+CONFIG_EXT_GROUP_SCHED=y
+CONFIG_BPF=y
+CONFIG_BPF_SYSCALL=y
+CONFIG_DEBUG_INFO=y
+CONFIG_DEBUG_INFO_BTF=y
diff --git a/tools/testing/selftests/sched_ext/create_dsq.bpf.c b/tools/testing/selftests/sched_ext/create_dsq.bpf.c
new file mode 100644
index 000000000000..23f79ed343f0
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/create_dsq.bpf.c
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Create and destroy DSQs in a loop.
+ *
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+void BPF_STRUCT_OPS(create_dsq_exit_task, struct task_struct *p,
+		    struct scx_exit_task_args *args)
+{
+	scx_bpf_destroy_dsq(p->pid);
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(create_dsq_init_task, struct task_struct *p,
+			     struct scx_init_task_args *args)
+{
+	s32 err;
+
+	err = scx_bpf_create_dsq(p->pid, -1);
+	if (err)
+		scx_bpf_error("Failed to create DSQ for %s[%d]",
+			      p->comm, p->pid);
+
+	return err;
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(create_dsq_init)
+{
+	u32 i;
+	s32 err;
+
+	bpf_for(i, 0, 1024) {
+		err = scx_bpf_create_dsq(i, -1);
+		if (err) {
+			scx_bpf_error("Failed to create DSQ %d", i);
+			return 0;
+		}
+	}
+
+	bpf_for(i, 0, 1024) {
+		scx_bpf_destroy_dsq(i);
+	}
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops create_dsq_ops = {
+	.init_task		= create_dsq_init_task,
+	.exit_task		= create_dsq_exit_task,
+	.init			= create_dsq_init,
+	.name			= "create_dsq",
+};
diff --git a/tools/testing/selftests/sched_ext/create_dsq.c b/tools/testing/selftests/sched_ext/create_dsq.c
new file mode 100644
index 000000000000..fa946d9146d4
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/create_dsq.c
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "create_dsq.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct create_dsq *skel;
+
+	skel = create_dsq__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load skel");
+		return SCX_TEST_FAIL;
+	}
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct create_dsq *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.create_dsq_ops);
+	if (!link) {
+		SCX_ERR("Failed to attach scheduler");
+		return SCX_TEST_FAIL;
+	}
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct create_dsq *skel = ctx;
+
+	create_dsq__destroy(skel);
+}
+
+struct scx_test create_dsq = {
+	.name = "create_dsq",
+	.description = "Create and destroy a dsq in a loop",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&create_dsq)
diff --git a/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c b/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c
new file mode 100644
index 000000000000..e97ad41d354a
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.bpf.c
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+UEI_DEFINE(uei);
+
+s32 BPF_STRUCT_OPS(ddsp_bogus_dsq_fail_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	s32 cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
+
+	if (cpu >= 0) {
+		/*
+		 * If we dispatch to a bogus DSQ that will fall back to the
+		 * builtin global DSQ, we fail gracefully.
+		 */
+		scx_bpf_dispatch_vtime(p, 0xcafef00d, SCX_SLICE_DFL,
+				       p->scx.dsq_vtime, 0);
+		return cpu;
+	}
+
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(ddsp_bogus_dsq_fail_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops ddsp_bogus_dsq_fail_ops = {
+	.select_cpu		= ddsp_bogus_dsq_fail_select_cpu,
+	.exit			= ddsp_bogus_dsq_fail_exit,
+	.name			= "ddsp_bogus_dsq_fail",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.c b/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.c
new file mode 100644
index 000000000000..e65d22f23f3b
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/ddsp_bogus_dsq_fail.c
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "ddsp_bogus_dsq_fail.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct ddsp_bogus_dsq_fail *skel;
+
+	skel = ddsp_bogus_dsq_fail__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct ddsp_bogus_dsq_fail *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.ddsp_bogus_dsq_fail_ops);
+	SCX_FAIL_IF(!link, "Failed to attach struct_ops");
+
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_ERROR));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct ddsp_bogus_dsq_fail *skel = ctx;
+
+	ddsp_bogus_dsq_fail__destroy(skel);
+}
+
+struct scx_test ddsp_bogus_dsq_fail = {
+	.name = "ddsp_bogus_dsq_fail",
+	.description = "Verify we gracefully fail, and fall back to using a "
+		       "built-in DSQ, if we do a direct dispatch to an invalid"
+		       " DSQ in ops.select_cpu()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&ddsp_bogus_dsq_fail)
diff --git a/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c b/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c
new file mode 100644
index 000000000000..dde7e7dafbfb
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.bpf.c
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+UEI_DEFINE(uei);
+
+s32 BPF_STRUCT_OPS(ddsp_vtimelocal_fail_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	s32 cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
+
+	if (cpu >= 0) {
+		/* Shouldn't be allowed to vtime dispatch to a builtin DSQ. */
+		scx_bpf_dispatch_vtime(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL,
+				       p->scx.dsq_vtime, 0);
+		return cpu;
+	}
+
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(ddsp_vtimelocal_fail_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops ddsp_vtimelocal_fail_ops = {
+	.select_cpu		= ddsp_vtimelocal_fail_select_cpu,
+	.exit			= ddsp_vtimelocal_fail_exit,
+	.name			= "ddsp_vtimelocal_fail",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.c b/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.c
new file mode 100644
index 000000000000..abafee587cd6
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/ddsp_vtimelocal_fail.c
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <unistd.h>
+#include "ddsp_vtimelocal_fail.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct ddsp_vtimelocal_fail *skel;
+
+	skel = ddsp_vtimelocal_fail__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct ddsp_vtimelocal_fail *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.ddsp_vtimelocal_fail_ops);
+	SCX_FAIL_IF(!link, "Failed to attach struct_ops");
+
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_ERROR));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct ddsp_vtimelocal_fail *skel = ctx;
+
+	ddsp_vtimelocal_fail__destroy(skel);
+}
+
+struct scx_test ddsp_vtimelocal_fail = {
+	.name = "ddsp_vtimelocal_fail",
+	.description = "Verify we gracefully fail, and fall back to using a "
+		       "built-in DSQ, if we do a direct vtime dispatch to a "
+		       "built-in DSQ from DSQ in ops.select_cpu()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&ddsp_vtimelocal_fail)
diff --git a/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c b/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c
new file mode 100644
index 000000000000..efb4672decb4
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/dsp_local_on.bpf.c
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+const volatile s32 nr_cpus;
+
+UEI_DEFINE(uei);
+
+struct {
+	__uint(type, BPF_MAP_TYPE_QUEUE);
+	__uint(max_entries, 8192);
+	__type(value, s32);
+} queue SEC(".maps");
+
+s32 BPF_STRUCT_OPS(dsp_local_on_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(dsp_local_on_enqueue, struct task_struct *p,
+		    u64 enq_flags)
+{
+	s32 pid = p->pid;
+
+	if (bpf_map_push_elem(&queue, &pid, 0))
+		scx_bpf_error("Failed to enqueue %s[%d]", p->comm, p->pid);
+}
+
+void BPF_STRUCT_OPS(dsp_local_on_dispatch, s32 cpu, struct task_struct *prev)
+{
+	s32 pid, target;
+	struct task_struct *p;
+
+	if (bpf_map_pop_elem(&queue, &pid))
+		return;
+
+	p = bpf_task_from_pid(pid);
+	if (!p)
+		return;
+
+	target = bpf_get_prandom_u32() % nr_cpus;
+
+	scx_bpf_dispatch(p, SCX_DSQ_LOCAL_ON | target, SCX_SLICE_DFL, 0);
+	bpf_task_release(p);
+}
+
+void BPF_STRUCT_OPS(dsp_local_on_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops dsp_local_on_ops = {
+	.select_cpu		= dsp_local_on_select_cpu,
+	.enqueue		= dsp_local_on_enqueue,
+	.dispatch		= dsp_local_on_dispatch,
+	.exit			= dsp_local_on_exit,
+	.name			= "dsp_local_on",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/dsp_local_on.c b/tools/testing/selftests/sched_ext/dsp_local_on.c
new file mode 100644
index 000000000000..472851b56854
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/dsp_local_on.c
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <unistd.h>
+#include "dsp_local_on.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct dsp_local_on *skel;
+
+	skel = dsp_local_on__open();
+	SCX_FAIL_IF(!skel, "Failed to open");
+
+	skel->rodata->nr_cpus = libbpf_num_possible_cpus();
+	SCX_FAIL_IF(dsp_local_on__load(skel), "Failed to load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct dsp_local_on *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.dsp_local_on_ops);
+	SCX_FAIL_IF(!link, "Failed to attach struct_ops");
+
+	/* Just sleeping is fine, plenty of scheduling events happening */
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_ERROR));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct dsp_local_on *skel = ctx;
+
+	dsp_local_on__destroy(skel);
+}
+
+struct scx_test dsp_local_on = {
+	.name = "dsp_local_on",
+	.description = "Verify we can directly dispatch tasks to a local DSQs "
+		       "from osp.dispatch()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&dsp_local_on)
diff --git a/tools/testing/selftests/sched_ext/enq_last_no_enq_fails.bpf.c b/tools/testing/selftests/sched_ext/enq_last_no_enq_fails.bpf.c
new file mode 100644
index 000000000000..b0b99531d5d5
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/enq_last_no_enq_fails.bpf.c
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates the behavior of direct dispatching with a default
+ * select_cpu implementation.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC(".struct_ops.link")
+struct sched_ext_ops enq_last_no_enq_fails_ops = {
+	.name			= "enq_last_no_enq_fails",
+	/* Need to define ops.enqueue() with SCX_OPS_ENQ_LAST */
+	.flags			= SCX_OPS_ENQ_LAST,
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/enq_last_no_enq_fails.c b/tools/testing/selftests/sched_ext/enq_last_no_enq_fails.c
new file mode 100644
index 000000000000..2a3eda5e2c0b
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/enq_last_no_enq_fails.c
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "enq_last_no_enq_fails.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct enq_last_no_enq_fails *skel;
+
+	skel = enq_last_no_enq_fails__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load skel");
+		return SCX_TEST_FAIL;
+	}
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct enq_last_no_enq_fails *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.enq_last_no_enq_fails_ops);
+	if (link) {
+		SCX_ERR("Incorrectly succeeded in to attaching scheduler");
+		return SCX_TEST_FAIL;
+	}
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct enq_last_no_enq_fails *skel = ctx;
+
+	enq_last_no_enq_fails__destroy(skel);
+}
+
+struct scx_test enq_last_no_enq_fails = {
+	.name = "enq_last_no_enq_fails",
+	.description = "Verify we fail to load a scheduler if we specify "
+		       "the SCX_OPS_ENQ_LAST flag without defining "
+		       "ops.enqueue()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&enq_last_no_enq_fails)
diff --git a/tools/testing/selftests/sched_ext/enq_select_cpu_fails.bpf.c b/tools/testing/selftests/sched_ext/enq_select_cpu_fails.bpf.c
new file mode 100644
index 000000000000..b3dfc1033cd6
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/enq_select_cpu_fails.bpf.c
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+/* Manually specify the signature until the kfunc is added to the scx repo. */
+s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
+			   bool *found) __ksym;
+
+s32 BPF_STRUCT_OPS(enq_select_cpu_fails_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(enq_select_cpu_fails_enqueue, struct task_struct *p,
+		    u64 enq_flags)
+{
+	/*
+	 * Need to initialize the variable or the verifier will fail to load.
+	 * Improving these semantics is actively being worked on.
+	 */
+	bool found = false;
+
+	/* Can only call from ops.select_cpu() */
+	scx_bpf_select_cpu_dfl(p, 0, 0, &found);
+
+	scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops enq_select_cpu_fails_ops = {
+	.select_cpu		= enq_select_cpu_fails_select_cpu,
+	.enqueue		= enq_select_cpu_fails_enqueue,
+	.name			= "enq_select_cpu_fails",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/enq_select_cpu_fails.c b/tools/testing/selftests/sched_ext/enq_select_cpu_fails.c
new file mode 100644
index 000000000000..dd1350e5f002
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/enq_select_cpu_fails.c
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "enq_select_cpu_fails.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct enq_select_cpu_fails *skel;
+
+	skel = enq_select_cpu_fails__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load skel");
+		return SCX_TEST_FAIL;
+	}
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct enq_select_cpu_fails *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.enq_select_cpu_fails_ops);
+	if (!link) {
+		SCX_ERR("Failed to attach scheduler");
+		return SCX_TEST_FAIL;
+	}
+
+	sleep(1);
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct enq_select_cpu_fails *skel = ctx;
+
+	enq_select_cpu_fails__destroy(skel);
+}
+
+struct scx_test enq_select_cpu_fails = {
+	.name = "enq_select_cpu_fails",
+	.description = "Verify we fail to call scx_bpf_select_cpu_dfl() "
+		       "from ops.enqueue()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&enq_select_cpu_fails)
diff --git a/tools/testing/selftests/sched_ext/exit.bpf.c b/tools/testing/selftests/sched_ext/exit.bpf.c
new file mode 100644
index 000000000000..ae12ddaac921
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/exit.bpf.c
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+#include "exit_test.h"
+
+const volatile int exit_point;
+UEI_DEFINE(uei);
+
+#define EXIT_CLEANLY() scx_bpf_exit(exit_point, "%d", exit_point)
+
+s32 BPF_STRUCT_OPS(exit_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	bool found;
+
+	if (exit_point == EXIT_SELECT_CPU)
+		EXIT_CLEANLY();
+
+	return scx_bpf_select_cpu_dfl(p, prev_cpu, wake_flags, &found);
+}
+
+void BPF_STRUCT_OPS(exit_enqueue, struct task_struct *p, u64 enq_flags)
+{
+	if (exit_point == EXIT_ENQUEUE)
+		EXIT_CLEANLY();
+
+	scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+void BPF_STRUCT_OPS(exit_dispatch, s32 cpu, struct task_struct *p)
+{
+	if (exit_point == EXIT_DISPATCH)
+		EXIT_CLEANLY();
+
+	scx_bpf_consume(SCX_DSQ_GLOBAL);
+}
+
+void BPF_STRUCT_OPS(exit_enable, struct task_struct *p)
+{
+	if (exit_point == EXIT_ENABLE)
+		EXIT_CLEANLY();
+}
+
+s32 BPF_STRUCT_OPS(exit_init_task, struct task_struct *p,
+		    struct scx_init_task_args *args)
+{
+	if (exit_point == EXIT_INIT_TASK)
+		EXIT_CLEANLY();
+
+	return 0;
+}
+
+void BPF_STRUCT_OPS(exit_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(exit_init)
+{
+	if (exit_point == EXIT_INIT)
+		EXIT_CLEANLY();
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops exit_ops = {
+	.select_cpu		= exit_select_cpu,
+	.enqueue		= exit_enqueue,
+	.dispatch		= exit_dispatch,
+	.init_task		= exit_init_task,
+	.enable			= exit_enable,
+	.exit			= exit_exit,
+	.init			= exit_init,
+	.name			= "exit",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/exit.c b/tools/testing/selftests/sched_ext/exit.c
new file mode 100644
index 000000000000..31bcd06e21cd
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/exit.c
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <sched.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "exit.bpf.skel.h"
+#include "scx_test.h"
+
+#include "exit_test.h"
+
+static enum scx_test_status run(void *ctx)
+{
+	enum exit_test_case tc;
+
+	for (tc = 0; tc < NUM_EXITS; tc++) {
+		struct exit *skel;
+		struct bpf_link *link;
+		char buf[16];
+
+		skel = exit__open();
+		skel->rodata->exit_point = tc;
+		exit__load(skel);
+		link = bpf_map__attach_struct_ops(skel->maps.exit_ops);
+		if (!link) {
+			SCX_ERR("Failed to attach scheduler");
+			exit__destroy(skel);
+			return SCX_TEST_FAIL;
+		}
+
+		/* Assumes uei.kind is written last */
+		while (skel->data->uei.kind == EXIT_KIND(SCX_EXIT_NONE))
+			sched_yield();
+
+		SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_UNREG_BPF));
+		SCX_EQ(skel->data->uei.exit_code, tc);
+		sprintf(buf, "%d", tc);
+		SCX_ASSERT(!strcmp(skel->data->uei.msg, buf));
+		bpf_link__destroy(link);
+		exit__destroy(skel);
+	}
+
+	return SCX_TEST_PASS;
+}
+
+struct scx_test exit_test = {
+	.name = "exit",
+	.description = "Verify we can cleanly exit a scheduler in multiple places",
+	.run = run,
+};
+REGISTER_SCX_TEST(&exit_test)
diff --git a/tools/testing/selftests/sched_ext/exit_test.h b/tools/testing/selftests/sched_ext/exit_test.h
new file mode 100644
index 000000000000..94f0268b9cb8
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/exit_test.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#ifndef __EXIT_TEST_H__
+#define __EXIT_TEST_H__
+
+enum exit_test_case {
+	EXIT_SELECT_CPU,
+	EXIT_ENQUEUE,
+	EXIT_DISPATCH,
+	EXIT_ENABLE,
+	EXIT_INIT_TASK,
+	EXIT_INIT,
+	NUM_EXITS,
+};
+
+#endif  // # __EXIT_TEST_H__
diff --git a/tools/testing/selftests/sched_ext/hotplug.bpf.c b/tools/testing/selftests/sched_ext/hotplug.bpf.c
new file mode 100644
index 000000000000..8f2601db39f3
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/hotplug.bpf.c
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+#include "hotplug_test.h"
+
+UEI_DEFINE(uei);
+
+void BPF_STRUCT_OPS(hotplug_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+static void exit_from_hotplug(s32 cpu, bool onlining)
+{
+	/*
+	 * Ignored, just used to verify that we can invoke blocking kfuncs
+	 * from the hotplug path.
+	 */
+	scx_bpf_create_dsq(0, -1);
+
+	s64 code = SCX_ECODE_ACT_RESTART | HOTPLUG_EXIT_RSN;
+
+	if (onlining)
+		code |= HOTPLUG_ONLINING;
+
+	scx_bpf_exit(code, "hotplug event detected (%d going %s)", cpu,
+		     onlining ? "online" : "offline");
+}
+
+void BPF_STRUCT_OPS_SLEEPABLE(hotplug_cpu_online, s32 cpu)
+{
+	exit_from_hotplug(cpu, true);
+}
+
+void BPF_STRUCT_OPS_SLEEPABLE(hotplug_cpu_offline, s32 cpu)
+{
+	exit_from_hotplug(cpu, false);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops hotplug_cb_ops = {
+	.cpu_online		= hotplug_cpu_online,
+	.cpu_offline		= hotplug_cpu_offline,
+	.exit			= hotplug_exit,
+	.name			= "hotplug_cbs",
+	.timeout_ms		= 1000U,
+};
+
+SEC(".struct_ops.link")
+struct sched_ext_ops hotplug_nocb_ops = {
+	.exit			= hotplug_exit,
+	.name			= "hotplug_nocbs",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/hotplug.c b/tools/testing/selftests/sched_ext/hotplug.c
new file mode 100644
index 000000000000..87bf220b1bce
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/hotplug.c
@@ -0,0 +1,168 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <sched.h>
+#include <scx/common.h>
+#include <sched.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include "hotplug_test.h"
+#include "hotplug.bpf.skel.h"
+#include "scx_test.h"
+#include "util.h"
+
+const char *online_path = "/sys/devices/system/cpu/cpu1/online";
+
+static bool is_cpu_online(void)
+{
+	return file_read_long(online_path) > 0;
+}
+
+static void toggle_online_status(bool online)
+{
+	long val = online ? 1 : 0;
+	int ret;
+
+	ret = file_write_long(online_path, val);
+	if (ret != 0)
+		fprintf(stderr, "Failed to bring CPU %s (%s)",
+			online ? "online" : "offline", strerror(errno));
+}
+
+static enum scx_test_status setup(void **ctx)
+{
+	if (!is_cpu_online())
+		return SCX_TEST_SKIP;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status test_hotplug(bool onlining, bool cbs_defined)
+{
+	struct hotplug *skel;
+	struct bpf_link *link;
+	long kind, code;
+
+	SCX_ASSERT(is_cpu_online());
+
+	skel = hotplug__open_and_load();
+	SCX_ASSERT(skel);
+
+	/* Testing the offline -> online path, so go offline before starting */
+	if (onlining)
+		toggle_online_status(0);
+
+	if (cbs_defined) {
+		kind = SCX_KIND_VAL(SCX_EXIT_UNREG_BPF);
+		code = SCX_ECODE_VAL(SCX_ECODE_ACT_RESTART) | HOTPLUG_EXIT_RSN;
+		if (onlining)
+			code |= HOTPLUG_ONLINING;
+	} else {
+		kind = SCX_KIND_VAL(SCX_EXIT_UNREG_KERN);
+		code = SCX_ECODE_VAL(SCX_ECODE_ACT_RESTART) |
+		       SCX_ECODE_VAL(SCX_ECODE_RSN_HOTPLUG);
+	}
+
+	if (cbs_defined)
+		link = bpf_map__attach_struct_ops(skel->maps.hotplug_cb_ops);
+	else
+		link = bpf_map__attach_struct_ops(skel->maps.hotplug_nocb_ops);
+
+	if (!link) {
+		SCX_ERR("Failed to attach scheduler");
+		hotplug__destroy(skel);
+		return SCX_TEST_FAIL;
+	}
+
+	toggle_online_status(onlining ? 1 : 0);
+
+	while (!UEI_EXITED(skel, uei))
+		sched_yield();
+
+	SCX_EQ(skel->data->uei.kind, kind);
+	SCX_EQ(UEI_REPORT(skel, uei), code);
+
+	if (!onlining)
+		toggle_online_status(1);
+
+	bpf_link__destroy(link);
+	hotplug__destroy(skel);
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status test_hotplug_attach(void)
+{
+	struct hotplug *skel;
+	struct bpf_link *link;
+	enum scx_test_status status = SCX_TEST_PASS;
+	long kind, code;
+
+	SCX_ASSERT(is_cpu_online());
+	SCX_ASSERT(scx_hotplug_seq() > 0);
+
+	skel = SCX_OPS_OPEN(hotplug_nocb_ops, hotplug);
+	SCX_ASSERT(skel);
+
+	SCX_OPS_LOAD(skel, hotplug_nocb_ops, hotplug, uei);
+
+	/*
+	 * Take the CPU offline to increment the global hotplug seq, which
+	 * should cause attach to fail due to us setting the hotplug seq above
+	 */
+	toggle_online_status(0);
+	link = bpf_map__attach_struct_ops(skel->maps.hotplug_nocb_ops);
+
+	toggle_online_status(1);
+
+	SCX_ASSERT(link);
+	while (!UEI_EXITED(skel, uei))
+		sched_yield();
+
+	kind = SCX_KIND_VAL(SCX_EXIT_UNREG_KERN);
+	code = SCX_ECODE_VAL(SCX_ECODE_ACT_RESTART) |
+	       SCX_ECODE_VAL(SCX_ECODE_RSN_HOTPLUG);
+	SCX_EQ(skel->data->uei.kind, kind);
+	SCX_EQ(UEI_REPORT(skel, uei), code);
+
+	bpf_link__destroy(link);
+	hotplug__destroy(skel);
+
+	return status;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+
+#define HP_TEST(__onlining, __cbs_defined) ({				\
+	if (test_hotplug(__onlining, __cbs_defined) != SCX_TEST_PASS)	\
+		return SCX_TEST_FAIL;					\
+})
+
+	HP_TEST(true, true);
+	HP_TEST(false, true);
+	HP_TEST(true, false);
+	HP_TEST(false, false);
+
+#undef HP_TEST
+
+	return test_hotplug_attach();
+}
+
+static void cleanup(void *ctx)
+{
+	toggle_online_status(1);
+}
+
+struct scx_test hotplug_test = {
+	.name = "hotplug",
+	.description = "Verify hotplug behavior",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&hotplug_test)
diff --git a/tools/testing/selftests/sched_ext/hotplug_test.h b/tools/testing/selftests/sched_ext/hotplug_test.h
new file mode 100644
index 000000000000..73d236f90787
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/hotplug_test.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#ifndef __HOTPLUG_TEST_H__
+#define __HOTPLUG_TEST_H__
+
+enum hotplug_test_flags {
+	HOTPLUG_EXIT_RSN = 1LLU << 0,
+	HOTPLUG_ONLINING = 1LLU << 1,
+};
+
+#endif  // # __HOTPLUG_TEST_H__
diff --git a/tools/testing/selftests/sched_ext/init_enable_count.bpf.c b/tools/testing/selftests/sched_ext/init_enable_count.bpf.c
new file mode 100644
index 000000000000..47ea89a626c3
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/init_enable_count.bpf.c
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that verifies that we do proper counting of init, enable, etc
+ * callbacks.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+u64 init_task_cnt, exit_task_cnt, enable_cnt, disable_cnt;
+u64 init_fork_cnt, init_transition_cnt;
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(cnt_init_task, struct task_struct *p,
+			     struct scx_init_task_args *args)
+{
+	__sync_fetch_and_add(&init_task_cnt, 1);
+
+	if (args->fork)
+		__sync_fetch_and_add(&init_fork_cnt, 1);
+	else
+		__sync_fetch_and_add(&init_transition_cnt, 1);
+
+	return 0;
+}
+
+void BPF_STRUCT_OPS(cnt_exit_task, struct task_struct *p)
+{
+	__sync_fetch_and_add(&exit_task_cnt, 1);
+}
+
+void BPF_STRUCT_OPS(cnt_enable, struct task_struct *p)
+{
+	__sync_fetch_and_add(&enable_cnt, 1);
+}
+
+void BPF_STRUCT_OPS(cnt_disable, struct task_struct *p)
+{
+	__sync_fetch_and_add(&disable_cnt, 1);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops init_enable_count_ops = {
+	.init_task	= cnt_init_task,
+	.exit_task	= cnt_exit_task,
+	.enable		= cnt_enable,
+	.disable	= cnt_disable,
+	.name		= "init_enable_count",
+};
diff --git a/tools/testing/selftests/sched_ext/init_enable_count.c b/tools/testing/selftests/sched_ext/init_enable_count.c
new file mode 100644
index 000000000000..97d45f1e5597
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/init_enable_count.c
@@ -0,0 +1,166 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <sched.h>
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include "scx_test.h"
+#include "init_enable_count.bpf.skel.h"
+
+#define SCHED_EXT 7
+
+static struct init_enable_count *
+open_load_prog(bool global)
+{
+	struct init_enable_count *skel;
+
+	skel = init_enable_count__open();
+	SCX_BUG_ON(!skel, "Failed to open skel");
+
+	if (!global)
+		skel->struct_ops.init_enable_count_ops->flags |= SCX_OPS_SWITCH_PARTIAL;
+
+	SCX_BUG_ON(init_enable_count__load(skel), "Failed to load skel");
+
+	return skel;
+}
+
+static enum scx_test_status run_test(bool global)
+{
+	struct init_enable_count *skel;
+	struct bpf_link *link;
+	const u32 num_children = 5, num_pre_forks = 1024;
+	int ret, i, status;
+	struct sched_param param = {};
+	pid_t pids[num_pre_forks];
+
+	skel = open_load_prog(global);
+
+	/*
+	 * Fork a bunch of children before we attach the scheduler so that we
+	 * ensure (at least in practical terms) that there are more tasks that
+	 * transition from SCHED_OTHER -> SCHED_EXT than there are tasks that
+	 * take the fork() path either below or in other processes.
+	 */
+	for (i = 0; i < num_pre_forks; i++) {
+		pids[i] = fork();
+		SCX_FAIL_IF(pids[i] < 0, "Failed to fork child");
+		if (pids[i] == 0) {
+			sleep(1);
+			exit(0);
+		}
+	}
+
+	link = bpf_map__attach_struct_ops(skel->maps.init_enable_count_ops);
+	SCX_FAIL_IF(!link, "Failed to attach struct_ops");
+
+	for (i = 0; i < num_pre_forks; i++) {
+		SCX_FAIL_IF(waitpid(pids[i], &status, 0) != pids[i],
+			    "Failed to wait for pre-forked child\n");
+
+		SCX_FAIL_IF(status != 0, "Pre-forked child %d exited with status %d\n", i,
+			    status);
+	}
+
+	bpf_link__destroy(link);
+	SCX_GE(skel->bss->init_task_cnt, num_pre_forks);
+	SCX_GE(skel->bss->exit_task_cnt, num_pre_forks);
+
+	link = bpf_map__attach_struct_ops(skel->maps.init_enable_count_ops);
+	SCX_FAIL_IF(!link, "Failed to attach struct_ops");
+
+	/* SCHED_EXT children */
+	for (i = 0; i < num_children; i++) {
+		pids[i] = fork();
+		SCX_FAIL_IF(pids[i] < 0, "Failed to fork child");
+
+		if (pids[i] == 0) {
+			ret = sched_setscheduler(0, SCHED_EXT, &param);
+			SCX_BUG_ON(ret, "Failed to set sched to sched_ext");
+
+			/*
+			 * Reset to SCHED_OTHER for half of them. Counts for
+			 * everything should still be the same regardless, as
+			 * ops.disable() is invoked even if a task is still on
+			 * SCHED_EXT before it exits.
+			 */
+			if (i % 2 == 0) {
+				ret = sched_setscheduler(0, SCHED_OTHER, &param);
+				SCX_BUG_ON(ret, "Failed to reset sched to normal");
+			}
+			exit(0);
+		}
+	}
+	for (i = 0; i < num_children; i++) {
+		SCX_FAIL_IF(waitpid(pids[i], &status, 0) != pids[i],
+			    "Failed to wait for SCX child\n");
+
+		SCX_FAIL_IF(status != 0, "SCX child %d exited with status %d\n", i,
+			    status);
+	}
+
+	/* SCHED_OTHER children */
+	for (i = 0; i < num_children; i++) {
+		pids[i] = fork();
+		if (pids[i] == 0)
+			exit(0);
+	}
+
+	for (i = 0; i < num_children; i++) {
+		SCX_FAIL_IF(waitpid(pids[i], &status, 0) != pids[i],
+			    "Failed to wait for normal child\n");
+
+		SCX_FAIL_IF(status != 0, "Normal child %d exited with status %d\n", i,
+			    status);
+	}
+
+	bpf_link__destroy(link);
+
+	SCX_GE(skel->bss->init_task_cnt, 2 * num_children);
+	SCX_GE(skel->bss->exit_task_cnt, 2 * num_children);
+
+	if (global) {
+		SCX_GE(skel->bss->enable_cnt, 2 * num_children);
+		SCX_GE(skel->bss->disable_cnt, 2 * num_children);
+	} else {
+		SCX_EQ(skel->bss->enable_cnt, num_children);
+		SCX_EQ(skel->bss->disable_cnt, num_children);
+	}
+	/*
+	 * We forked a ton of tasks before we attached the scheduler above, so
+	 * this should be fine. Technically it could be flaky if a ton of forks
+	 * are happening at the same time in other processes, but that should
+	 * be exceedingly unlikely.
+	 */
+	SCX_GT(skel->bss->init_transition_cnt, skel->bss->init_fork_cnt);
+	SCX_GE(skel->bss->init_fork_cnt, 2 * num_children);
+
+	init_enable_count__destroy(skel);
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	enum scx_test_status status;
+
+	status = run_test(true);
+	if (status != SCX_TEST_PASS)
+		return status;
+
+	return run_test(false);
+}
+
+struct scx_test init_enable_count = {
+	.name = "init_enable_count",
+	.description = "Verify we do the correct amount of counting of init, "
+		       "enable, etc callbacks.",
+	.run = run,
+};
+REGISTER_SCX_TEST(&init_enable_count)
diff --git a/tools/testing/selftests/sched_ext/maximal.bpf.c b/tools/testing/selftests/sched_ext/maximal.bpf.c
new file mode 100644
index 000000000000..44612fdaf399
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/maximal.bpf.c
@@ -0,0 +1,132 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler with every callback defined.
+ *
+ * This scheduler defines every callback.
+ *
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+s32 BPF_STRUCT_OPS(maximal_select_cpu, struct task_struct *p, s32 prev_cpu,
+		   u64 wake_flags)
+{
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(maximal_enqueue, struct task_struct *p, u64 enq_flags)
+{
+	scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+void BPF_STRUCT_OPS(maximal_dequeue, struct task_struct *p, u64 deq_flags)
+{}
+
+void BPF_STRUCT_OPS(maximal_dispatch, s32 cpu, struct task_struct *prev)
+{
+	scx_bpf_consume(SCX_DSQ_GLOBAL);
+}
+
+void BPF_STRUCT_OPS(maximal_runnable, struct task_struct *p, u64 enq_flags)
+{}
+
+void BPF_STRUCT_OPS(maximal_running, struct task_struct *p)
+{}
+
+void BPF_STRUCT_OPS(maximal_stopping, struct task_struct *p, bool runnable)
+{}
+
+void BPF_STRUCT_OPS(maximal_quiescent, struct task_struct *p, u64 deq_flags)
+{}
+
+bool BPF_STRUCT_OPS(maximal_yield, struct task_struct *from,
+		    struct task_struct *to)
+{
+	return false;
+}
+
+bool BPF_STRUCT_OPS(maximal_core_sched_before, struct task_struct *a,
+		    struct task_struct *b)
+{
+	return false;
+}
+
+void BPF_STRUCT_OPS(maximal_set_weight, struct task_struct *p, u32 weight)
+{}
+
+void BPF_STRUCT_OPS(maximal_set_cpumask, struct task_struct *p,
+		    const struct cpumask *cpumask)
+{}
+
+void BPF_STRUCT_OPS(maximal_update_idle, s32 cpu, bool idle)
+{}
+
+void BPF_STRUCT_OPS(maximal_cpu_acquire, s32 cpu,
+		    struct scx_cpu_acquire_args *args)
+{}
+
+void BPF_STRUCT_OPS(maximal_cpu_release, s32 cpu,
+		    struct scx_cpu_release_args *args)
+{}
+
+void BPF_STRUCT_OPS(maximal_cpu_online, s32 cpu)
+{}
+
+void BPF_STRUCT_OPS(maximal_cpu_offline, s32 cpu)
+{}
+
+s32 BPF_STRUCT_OPS(maximal_init_task, struct task_struct *p,
+		   struct scx_init_task_args *args)
+{
+	return 0;
+}
+
+void BPF_STRUCT_OPS(maximal_enable, struct task_struct *p)
+{}
+
+void BPF_STRUCT_OPS(maximal_exit_task, struct task_struct *p,
+		    struct scx_exit_task_args *args)
+{}
+
+void BPF_STRUCT_OPS(maximal_disable, struct task_struct *p)
+{}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(maximal_init)
+{
+	return 0;
+}
+
+void BPF_STRUCT_OPS(maximal_exit, struct scx_exit_info *info)
+{}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops maximal_ops = {
+	.select_cpu		= maximal_select_cpu,
+	.enqueue		= maximal_enqueue,
+	.dequeue		= maximal_dequeue,
+	.dispatch		= maximal_dispatch,
+	.runnable		= maximal_runnable,
+	.running		= maximal_running,
+	.stopping		= maximal_stopping,
+	.quiescent		= maximal_quiescent,
+	.yield			= maximal_yield,
+	.core_sched_before	= maximal_core_sched_before,
+	.set_weight		= maximal_set_weight,
+	.set_cpumask		= maximal_set_cpumask,
+	.update_idle		= maximal_update_idle,
+	.cpu_acquire		= maximal_cpu_acquire,
+	.cpu_release		= maximal_cpu_release,
+	.cpu_online		= maximal_cpu_online,
+	.cpu_offline		= maximal_cpu_offline,
+	.init_task		= maximal_init_task,
+	.enable			= maximal_enable,
+	.exit_task		= maximal_exit_task,
+	.disable		= maximal_disable,
+	.init			= maximal_init,
+	.exit			= maximal_exit,
+	.name			= "maximal",
+};
diff --git a/tools/testing/selftests/sched_ext/maximal.c b/tools/testing/selftests/sched_ext/maximal.c
new file mode 100644
index 000000000000..f38fc973c380
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/maximal.c
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "maximal.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct maximal *skel;
+
+	skel = maximal__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct maximal *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.maximal_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct maximal *skel = ctx;
+
+	maximal__destroy(skel);
+}
+
+struct scx_test maximal = {
+	.name = "maximal",
+	.description = "Verify we can load a scheduler with every callback defined",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&maximal)
diff --git a/tools/testing/selftests/sched_ext/maybe_null.bpf.c b/tools/testing/selftests/sched_ext/maybe_null.bpf.c
new file mode 100644
index 000000000000..27d0f386acfb
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/maybe_null.bpf.c
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+u64 vtime_test;
+
+void BPF_STRUCT_OPS(maybe_null_running, struct task_struct *p)
+{}
+
+void BPF_STRUCT_OPS(maybe_null_success_dispatch, s32 cpu, struct task_struct *p)
+{
+	if (p != NULL)
+		vtime_test = p->scx.dsq_vtime;
+}
+
+bool BPF_STRUCT_OPS(maybe_null_success_yield, struct task_struct *from,
+		    struct task_struct *to)
+{
+	if (to)
+		bpf_printk("Yielding to %s[%d]", to->comm, to->pid);
+
+	return false;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops maybe_null_success = {
+	.dispatch               = maybe_null_success_dispatch,
+	.yield			= maybe_null_success_yield,
+	.enable			= maybe_null_running,
+	.name			= "minimal",
+};
diff --git a/tools/testing/selftests/sched_ext/maybe_null.c b/tools/testing/selftests/sched_ext/maybe_null.c
new file mode 100644
index 000000000000..31cfafb0cf65
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/maybe_null.c
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "maybe_null.bpf.skel.h"
+#include "maybe_null_fail_dsp.bpf.skel.h"
+#include "maybe_null_fail_yld.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status run(void *ctx)
+{
+	struct maybe_null *skel;
+	struct maybe_null_fail_dsp *fail_dsp;
+	struct maybe_null_fail_yld *fail_yld;
+
+	skel = maybe_null__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load maybe_null skel");
+		return SCX_TEST_FAIL;
+	}
+	maybe_null__destroy(skel);
+
+	fail_dsp = maybe_null_fail_dsp__open_and_load();
+	if (fail_dsp) {
+		maybe_null_fail_dsp__destroy(fail_dsp);
+		SCX_ERR("Should failed to open and load maybe_null_fail_dsp skel");
+		return SCX_TEST_FAIL;
+	}
+
+	fail_yld = maybe_null_fail_yld__open_and_load();
+	if (fail_yld) {
+		maybe_null_fail_yld__destroy(fail_yld);
+		SCX_ERR("Should failed to open and load maybe_null_fail_yld skel");
+		return SCX_TEST_FAIL;
+	}
+
+	return SCX_TEST_PASS;
+}
+
+struct scx_test maybe_null = {
+	.name = "maybe_null",
+	.description = "Verify if PTR_MAYBE_NULL work for .dispatch",
+	.run = run,
+};
+REGISTER_SCX_TEST(&maybe_null)
diff --git a/tools/testing/selftests/sched_ext/maybe_null_fail_dsp.bpf.c b/tools/testing/selftests/sched_ext/maybe_null_fail_dsp.bpf.c
new file mode 100644
index 000000000000..c0641050271d
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/maybe_null_fail_dsp.bpf.c
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+u64 vtime_test;
+
+void BPF_STRUCT_OPS(maybe_null_running, struct task_struct *p)
+{}
+
+void BPF_STRUCT_OPS(maybe_null_fail_dispatch, s32 cpu, struct task_struct *p)
+{
+	vtime_test = p->scx.dsq_vtime;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops maybe_null_fail = {
+	.dispatch               = maybe_null_fail_dispatch,
+	.enable			= maybe_null_running,
+	.name			= "maybe_null_fail_dispatch",
+};
diff --git a/tools/testing/selftests/sched_ext/maybe_null_fail_yld.bpf.c b/tools/testing/selftests/sched_ext/maybe_null_fail_yld.bpf.c
new file mode 100644
index 000000000000..3c1740028e3b
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/maybe_null_fail_yld.bpf.c
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+u64 vtime_test;
+
+void BPF_STRUCT_OPS(maybe_null_running, struct task_struct *p)
+{}
+
+bool BPF_STRUCT_OPS(maybe_null_fail_yield, struct task_struct *from,
+		    struct task_struct *to)
+{
+	bpf_printk("Yielding to %s[%d]", to->comm, to->pid);
+
+	return false;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops maybe_null_fail = {
+	.yield			= maybe_null_fail_yield,
+	.enable			= maybe_null_running,
+	.name			= "maybe_null_fail_yield",
+};
diff --git a/tools/testing/selftests/sched_ext/minimal.bpf.c b/tools/testing/selftests/sched_ext/minimal.bpf.c
new file mode 100644
index 000000000000..6a7eccef0104
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/minimal.bpf.c
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A completely minimal scheduler.
+ *
+ * This scheduler defines the absolute minimal set of struct sched_ext_ops
+ * fields: its name. It should _not_ fail to be loaded, and can be used to
+ * exercise the default scheduling paths in ext.c.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+SEC(".struct_ops.link")
+struct sched_ext_ops minimal_ops = {
+	.name			= "minimal",
+};
diff --git a/tools/testing/selftests/sched_ext/minimal.c b/tools/testing/selftests/sched_ext/minimal.c
new file mode 100644
index 000000000000..6c5db8ebbf8a
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/minimal.c
@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "minimal.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct minimal *skel;
+
+	skel = minimal__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load skel");
+		return SCX_TEST_FAIL;
+	}
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct minimal *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.minimal_ops);
+	if (!link) {
+		SCX_ERR("Failed to attach scheduler");
+		return SCX_TEST_FAIL;
+	}
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct minimal *skel = ctx;
+
+	minimal__destroy(skel);
+}
+
+struct scx_test minimal = {
+	.name = "minimal",
+	.description = "Verify we can load a fully minimal scheduler",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&minimal)
diff --git a/tools/testing/selftests/sched_ext/prog_run.bpf.c b/tools/testing/selftests/sched_ext/prog_run.bpf.c
new file mode 100644
index 000000000000..fd2c8f12af16
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/prog_run.bpf.c
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates that we can invoke sched_ext kfuncs in
+ * BPF_PROG_TYPE_SYSCALL programs.
+ *
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+
+#include <scx/common.bpf.h>
+
+UEI_DEFINE(uei);
+
+char _license[] SEC("license") = "GPL";
+
+SEC("syscall")
+int BPF_PROG(prog_run_syscall)
+{
+	scx_bpf_exit(0xdeadbeef, "Exited from PROG_RUN");
+	return 0;
+}
+
+void BPF_STRUCT_OPS(prog_run_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops prog_run_ops = {
+	.exit			= prog_run_exit,
+	.name			= "prog_run",
+};
diff --git a/tools/testing/selftests/sched_ext/prog_run.c b/tools/testing/selftests/sched_ext/prog_run.c
new file mode 100644
index 000000000000..3cd57ef8daaa
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/prog_run.c
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <sched.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "prog_run.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct prog_run *skel;
+
+	skel = prog_run__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load skel");
+		return SCX_TEST_FAIL;
+	}
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct prog_run *skel = ctx;
+	struct bpf_link *link;
+	int prog_fd, err = 0;
+
+	prog_fd = bpf_program__fd(skel->progs.prog_run_syscall);
+	if (prog_fd < 0) {
+		SCX_ERR("Failed to get BPF_PROG_RUN prog");
+		return SCX_TEST_FAIL;
+	}
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+
+	link = bpf_map__attach_struct_ops(skel->maps.prog_run_ops);
+	if (!link) {
+		SCX_ERR("Failed to attach scheduler");
+		close(prog_fd);
+		return SCX_TEST_FAIL;
+	}
+
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	SCX_EQ(err, 0);
+
+	/* Assumes uei.kind is written last */
+	while (skel->data->uei.kind == EXIT_KIND(SCX_EXIT_NONE))
+		sched_yield();
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_UNREG_BPF));
+	SCX_EQ(skel->data->uei.exit_code, 0xdeadbeef);
+	close(prog_fd);
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct prog_run *skel = ctx;
+
+	prog_run__destroy(skel);
+}
+
+struct scx_test prog_run = {
+	.name = "prog_run",
+	.description = "Verify we can call into a scheduler with BPF_PROG_RUN, and invoke kfuncs",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&prog_run)
diff --git a/tools/testing/selftests/sched_ext/reload_loop.c b/tools/testing/selftests/sched_ext/reload_loop.c
new file mode 100644
index 000000000000..5cfba2d6e056
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/reload_loop.c
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <pthread.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "maximal.bpf.skel.h"
+#include "scx_test.h"
+
+static struct maximal *skel;
+static pthread_t threads[2];
+
+bool force_exit = false;
+
+static enum scx_test_status setup(void **ctx)
+{
+	skel = maximal__open_and_load();
+	if (!skel) {
+		SCX_ERR("Failed to open and load skel");
+		return SCX_TEST_FAIL;
+	}
+
+	return SCX_TEST_PASS;
+}
+
+static void *do_reload_loop(void *arg)
+{
+	u32 i;
+
+	for (i = 0; i < 1024 && !force_exit; i++) {
+		struct bpf_link *link;
+
+		link = bpf_map__attach_struct_ops(skel->maps.maximal_ops);
+		if (link)
+			bpf_link__destroy(link);
+	}
+
+	return NULL;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	int err;
+	void *ret;
+
+	err = pthread_create(&threads[0], NULL, do_reload_loop, NULL);
+	SCX_FAIL_IF(err, "Failed to create thread 0");
+
+	err = pthread_create(&threads[1], NULL, do_reload_loop, NULL);
+	SCX_FAIL_IF(err, "Failed to create thread 1");
+
+	SCX_FAIL_IF(pthread_join(threads[0], &ret), "thread 0 failed");
+	SCX_FAIL_IF(pthread_join(threads[1], &ret), "thread 1 failed");
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	force_exit = true;
+	maximal__destroy(skel);
+}
+
+struct scx_test reload_loop = {
+	.name = "reload_loop",
+	.description = "Stress test loading and unloading schedulers repeatedly in a tight loop",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&reload_loop)
diff --git a/tools/testing/selftests/sched_ext/runner.c b/tools/testing/selftests/sched_ext/runner.c
new file mode 100644
index 000000000000..eab48c7ff309
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/runner.c
@@ -0,0 +1,201 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+#include <stdio.h>
+#include <unistd.h>
+#include <signal.h>
+#include <libgen.h>
+#include <bpf/bpf.h>
+#include "scx_test.h"
+
+const char help_fmt[] =
+"The runner for sched_ext tests.\n"
+"\n"
+"The runner is statically linked against all testcases, and runs them all serially.\n"
+"It's required for the testcases to be serial, as only a single host-wide sched_ext\n"
+"scheduler may be loaded at any given time."
+"\n"
+"Usage: %s [-t TEST] [-h]\n"
+"\n"
+"  -t TEST       Only run tests whose name includes this string\n"
+"  -s            Include print output for skipped tests\n"
+"  -q            Don't print the test descriptions during run\n"
+"  -h            Display this help and exit\n";
+
+static volatile int exit_req;
+static bool quiet, print_skipped;
+
+#define MAX_SCX_TESTS 2048
+
+static struct scx_test __scx_tests[MAX_SCX_TESTS];
+static unsigned __scx_num_tests = 0;
+
+static void sigint_handler(int simple)
+{
+	exit_req = 1;
+}
+
+static void print_test_preamble(const struct scx_test *test, bool quiet)
+{
+	printf("===== START =====\n");
+	printf("TEST: %s\n", test->name);
+	if (!quiet)
+		printf("DESCRIPTION: %s\n", test->description);
+	printf("OUTPUT:\n");
+}
+
+static const char *status_to_result(enum scx_test_status status)
+{
+	switch (status) {
+	case SCX_TEST_PASS:
+	case SCX_TEST_SKIP:
+		return "ok";
+	case SCX_TEST_FAIL:
+		return "not ok";
+	default:
+		return "<UNKNOWN>";
+	}
+}
+
+static void print_test_result(const struct scx_test *test,
+			      enum scx_test_status status,
+			      unsigned int testnum)
+{
+	const char *result = status_to_result(status);
+	const char *directive = status == SCX_TEST_SKIP ? "SKIP " : "";
+
+	printf("%s %u %s # %s\n", result, testnum, test->name, directive);
+	printf("=====  END  =====\n");
+}
+
+static bool should_skip_test(const struct scx_test *test, const char * filter)
+{
+	return !strstr(test->name, filter);
+}
+
+static enum scx_test_status run_test(const struct scx_test *test)
+{
+	enum scx_test_status status;
+	void *context = NULL;
+
+	if (test->setup) {
+		status = test->setup(&context);
+		if (status != SCX_TEST_PASS)
+			return status;
+	}
+
+	status = test->run(context);
+
+	if (test->cleanup)
+		test->cleanup(context);
+
+	return status;
+}
+
+static bool test_valid(const struct scx_test *test)
+{
+	if (!test) {
+		fprintf(stderr, "NULL test detected\n");
+		return false;
+	}
+
+	if (!test->name) {
+		fprintf(stderr,
+			"Test with no name found. Must specify test name.\n");
+		return false;
+	}
+
+	if (!test->description) {
+		fprintf(stderr, "Test %s requires description.\n", test->name);
+		return false;
+	}
+
+	if (!test->run) {
+		fprintf(stderr, "Test %s has no run() callback\n", test->name);
+		return false;
+	}
+
+	return true;
+}
+
+int main(int argc, char **argv)
+{
+	const char *filter = NULL;
+	unsigned testnum = 0, i;
+	unsigned passed = 0, skipped = 0, failed = 0;
+	int opt;
+
+	signal(SIGINT, sigint_handler);
+	signal(SIGTERM, sigint_handler);
+
+	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+
+	while ((opt = getopt(argc, argv, "qst:h")) != -1) {
+		switch (opt) {
+		case 'q':
+			quiet = true;
+			break;
+		case 's':
+			print_skipped = true;
+			break;
+		case 't':
+			filter = optarg;
+			break;
+		default:
+			fprintf(stderr, help_fmt, basename(argv[0]));
+			return opt != 'h';
+		}
+	}
+
+	for (i = 0; i < __scx_num_tests; i++) {
+		enum scx_test_status status;
+		struct scx_test *test = &__scx_tests[i];
+
+		if (filter && should_skip_test(test, filter)) {
+			/*
+			 * Printing the skipped tests and their preambles can
+			 * add a lot of noise to the runner output. Printing
+			 * this is only really useful for CI, so let's skip it
+			 * by default.
+			 */
+			if (print_skipped) {
+				print_test_preamble(test, quiet);
+				print_test_result(test, SCX_TEST_SKIP, ++testnum);
+			}
+			continue;
+		}
+
+		print_test_preamble(test, quiet);
+		status = run_test(test);
+		print_test_result(test, status, ++testnum);
+		switch (status) {
+		case SCX_TEST_PASS:
+			passed++;
+			break;
+		case SCX_TEST_SKIP:
+			skipped++;
+			break;
+		case SCX_TEST_FAIL:
+			failed++;
+			break;
+		}
+	}
+	printf("\n\n=============================\n\n");
+	printf("RESULTS:\n\n");
+	printf("PASSED:  %u\n", passed);
+	printf("SKIPPED: %u\n", skipped);
+	printf("FAILED:  %u\n", failed);
+
+	return 0;
+}
+
+void scx_test_register(struct scx_test *test)
+{
+	SCX_BUG_ON(!test_valid(test), "Invalid test found");
+	SCX_BUG_ON(__scx_num_tests >= MAX_SCX_TESTS, "Maximum tests exceeded");
+
+	__scx_tests[__scx_num_tests++] = *test;
+}
diff --git a/tools/testing/selftests/sched_ext/scx_test.h b/tools/testing/selftests/sched_ext/scx_test.h
new file mode 100644
index 000000000000..90b8d6915bb7
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/scx_test.h
@@ -0,0 +1,131 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ */
+
+#ifndef __SCX_TEST_H__
+#define __SCX_TEST_H__
+
+#include <errno.h>
+#include <scx/common.h>
+#include <scx/compat.h>
+
+enum scx_test_status {
+	SCX_TEST_PASS = 0,
+	SCX_TEST_SKIP,
+	SCX_TEST_FAIL,
+};
+
+#define EXIT_KIND(__ent) __COMPAT_ENUM_OR_ZERO("scx_exit_kind", #__ent)
+
+struct scx_test {
+	/**
+	 * name - The name of the testcase.
+	 */
+	const char *name;
+
+	/**
+	 * description - A description of your testcase: what it tests and is
+	 * meant to validate.
+	 */
+	const char *description;
+
+	/*
+	 * setup - Setup the test.
+	 * @ctx: A pointer to a context object that will be passed to run and
+	 *	 cleanup.
+	 *
+	 * An optional callback that allows a testcase to perform setup for its
+	 * run. A test may return SCX_TEST_SKIP to skip the run.
+	 */
+	enum scx_test_status (*setup)(void **ctx);
+
+	/*
+	 * run - Run the test.
+	 * @ctx: Context set in the setup() callback. If @ctx was not set in
+	 *	 setup(), it is NULL.
+	 *
+	 * The main test. Callers should return one of:
+	 *
+	 * - SCX_TEST_PASS: Test passed
+	 * - SCX_TEST_SKIP: Test should be skipped
+	 * - SCX_TEST_FAIL: Test failed
+	 *
+	 * This callback must be defined.
+	 */
+	enum scx_test_status (*run)(void *ctx);
+
+	/*
+	 * cleanup - Perform cleanup following the test
+	 * @ctx: Context set in the setup() callback. If @ctx was not set in
+	 *	 setup(), it is NULL.
+	 *
+	 * An optional callback that allows a test to perform cleanup after
+	 * being run. This callback is run even if the run() callback returns
+	 * SCX_TEST_SKIP or SCX_TEST_FAIL. It is not run if setup() returns
+	 * SCX_TEST_SKIP or SCX_TEST_FAIL.
+	 */
+	void (*cleanup)(void *ctx);
+};
+
+void scx_test_register(struct scx_test *test);
+
+#define REGISTER_SCX_TEST(__test)			\
+	__attribute__((constructor))			\
+	static void ___scxregister##__LINE__(void)	\
+	{						\
+		scx_test_register(__test);		\
+	}
+
+#define SCX_ERR(__fmt, ...)						\
+	do {								\
+		fprintf(stderr, "ERR: %s:%d\n", __FILE__, __LINE__);	\
+		fprintf(stderr, __fmt"\n", ##__VA_ARGS__);			\
+	} while (0)
+
+#define SCX_FAIL(__fmt, ...)						\
+	do {								\
+		SCX_ERR(__fmt, ##__VA_ARGS__);				\
+		return SCX_TEST_FAIL;					\
+	} while (0)
+
+#define SCX_FAIL_IF(__cond, __fmt, ...)					\
+	do {								\
+		if (__cond)						\
+			SCX_FAIL(__fmt, ##__VA_ARGS__);			\
+	} while (0)
+
+#define SCX_GT(_x, _y) SCX_FAIL_IF((_x) <= (_y), "Expected %s > %s (%lu > %lu)",	\
+				   #_x, #_y, (u64)(_x), (u64)(_y))
+#define SCX_GE(_x, _y) SCX_FAIL_IF((_x) < (_y), "Expected %s >= %s (%lu >= %lu)",	\
+				   #_x, #_y, (u64)(_x), (u64)(_y))
+#define SCX_LT(_x, _y) SCX_FAIL_IF((_x) >= (_y), "Expected %s < %s (%lu < %lu)",	\
+				   #_x, #_y, (u64)(_x), (u64)(_y))
+#define SCX_LE(_x, _y) SCX_FAIL_IF((_x) > (_y), "Expected %s <= %s (%lu <= %lu)",	\
+				   #_x, #_y, (u64)(_x), (u64)(_y))
+#define SCX_EQ(_x, _y) SCX_FAIL_IF((_x) != (_y), "Expected %s == %s (%lu == %lu)",	\
+				   #_x, #_y, (u64)(_x), (u64)(_y))
+#define SCX_ASSERT(_x) SCX_FAIL_IF(!(_x), "Expected %s to be true (%lu)",		\
+				   #_x, (u64)(_x))
+
+#define SCX_ECODE_VAL(__ecode) ({						\
+        u64 __val = 0;								\
+	bool __found = false;							\
+										\
+	__found = __COMPAT_read_enum("scx_exit_code", #__ecode, &__val);	\
+	SCX_ASSERT(__found);							\
+	(s64)__val;								\
+})
+
+#define SCX_KIND_VAL(__kind) ({							\
+        u64 __val = 0;								\
+	bool __found = false;							\
+										\
+	__found = __COMPAT_read_enum("scx_exit_kind", #__kind, &__val);		\
+	SCX_ASSERT(__found);							\
+	__val;									\
+})
+
+#endif  // # __SCX_TEST_H__
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dfl.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_dfl.bpf.c
new file mode 100644
index 000000000000..2ed2991afafe
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dfl.bpf.c
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates the behavior of direct dispatching with a default
+ * select_cpu implementation.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+bool saw_local = false;
+
+static bool task_is_test(const struct task_struct *p)
+{
+	return !bpf_strncmp(p->comm, 9, "select_cpu");
+}
+
+void BPF_STRUCT_OPS(select_cpu_dfl_enqueue, struct task_struct *p,
+		    u64 enq_flags)
+{
+	const struct cpumask *idle_mask = scx_bpf_get_idle_cpumask();
+
+	if (task_is_test(p) &&
+	    bpf_cpumask_test_cpu(scx_bpf_task_cpu(p), idle_mask)) {
+		saw_local = true;
+	}
+	scx_bpf_put_idle_cpumask(idle_mask);
+
+	scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops select_cpu_dfl_ops = {
+	.enqueue		= select_cpu_dfl_enqueue,
+	.name			= "select_cpu_dfl",
+};
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dfl.c b/tools/testing/selftests/sched_ext/select_cpu_dfl.c
new file mode 100644
index 000000000000..a53a40c2d2f0
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dfl.c
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "select_cpu_dfl.bpf.skel.h"
+#include "scx_test.h"
+
+#define NUM_CHILDREN 1028
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct select_cpu_dfl *skel;
+
+	skel = select_cpu_dfl__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct select_cpu_dfl *skel = ctx;
+	struct bpf_link *link;
+	pid_t pids[NUM_CHILDREN];
+	int i, status;
+
+	link = bpf_map__attach_struct_ops(skel->maps.select_cpu_dfl_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	for (i = 0; i < NUM_CHILDREN; i++) {
+		pids[i] = fork();
+		if (pids[i] == 0) {
+			sleep(1);
+			exit(0);
+		}
+	}
+
+	for (i = 0; i < NUM_CHILDREN; i++) {
+		SCX_EQ(waitpid(pids[i], &status, 0), pids[i]);
+		SCX_EQ(status, 0);
+	}
+
+	SCX_ASSERT(!skel->bss->saw_local);
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct select_cpu_dfl *skel = ctx;
+
+	select_cpu_dfl__destroy(skel);
+}
+
+struct scx_test select_cpu_dfl = {
+	.name = "select_cpu_dfl",
+	.description = "Verify the default ops.select_cpu() dispatches tasks "
+		       "when idles cores are found, and skips ops.enqueue()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&select_cpu_dfl)
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.bpf.c
new file mode 100644
index 000000000000..4bb5abb2d369
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.bpf.c
@@ -0,0 +1,89 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates the behavior of direct dispatching with a default
+ * select_cpu implementation, and with the SCX_OPS_ENQ_DFL_NO_DISPATCH ops flag
+ * specified.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+bool saw_local = false;
+
+/* Per-task scheduling context */
+struct task_ctx {
+	bool	force_local;	/* CPU changed by ops.select_cpu() */
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+	__uint(map_flags, BPF_F_NO_PREALLOC);
+	__type(key, int);
+	__type(value, struct task_ctx);
+} task_ctx_stor SEC(".maps");
+
+/* Manually specify the signature until the kfunc is added to the scx repo. */
+s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
+			   bool *found) __ksym;
+
+s32 BPF_STRUCT_OPS(select_cpu_dfl_nodispatch_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	struct task_ctx *tctx;
+	s32 cpu;
+
+	tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
+	if (!tctx) {
+		scx_bpf_error("task_ctx lookup failed");
+		return -ESRCH;
+	}
+
+	cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, wake_flags,
+				     &tctx->force_local);
+
+	return cpu;
+}
+
+void BPF_STRUCT_OPS(select_cpu_dfl_nodispatch_enqueue, struct task_struct *p,
+		    u64 enq_flags)
+{
+	u64 dsq_id = SCX_DSQ_GLOBAL;
+	struct task_ctx *tctx;
+
+	tctx = bpf_task_storage_get(&task_ctx_stor, p, 0, 0);
+	if (!tctx) {
+		scx_bpf_error("task_ctx lookup failed");
+		return;
+	}
+
+	if (tctx->force_local) {
+		dsq_id = SCX_DSQ_LOCAL;
+		tctx->force_local = false;
+		saw_local = true;
+	}
+
+	scx_bpf_dispatch(p, dsq_id, SCX_SLICE_DFL, enq_flags);
+}
+
+s32 BPF_STRUCT_OPS(select_cpu_dfl_nodispatch_init_task,
+		   struct task_struct *p, struct scx_init_task_args *args)
+{
+	if (bpf_task_storage_get(&task_ctx_stor, p, 0,
+				 BPF_LOCAL_STORAGE_GET_F_CREATE))
+		return 0;
+	else
+		return -ENOMEM;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops select_cpu_dfl_nodispatch_ops = {
+	.select_cpu		= select_cpu_dfl_nodispatch_select_cpu,
+	.enqueue		= select_cpu_dfl_nodispatch_enqueue,
+	.init_task		= select_cpu_dfl_nodispatch_init_task,
+	.name			= "select_cpu_dfl_nodispatch",
+};
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.c b/tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.c
new file mode 100644
index 000000000000..1d85bf4bf3a3
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dfl_nodispatch.c
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "select_cpu_dfl_nodispatch.bpf.skel.h"
+#include "scx_test.h"
+
+#define NUM_CHILDREN 1028
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct select_cpu_dfl_nodispatch *skel;
+
+	skel = select_cpu_dfl_nodispatch__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct select_cpu_dfl_nodispatch *skel = ctx;
+	struct bpf_link *link;
+	pid_t pids[NUM_CHILDREN];
+	int i, status;
+
+	link = bpf_map__attach_struct_ops(skel->maps.select_cpu_dfl_nodispatch_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	for (i = 0; i < NUM_CHILDREN; i++) {
+		pids[i] = fork();
+		if (pids[i] == 0) {
+			sleep(1);
+			exit(0);
+		}
+	}
+
+	for (i = 0; i < NUM_CHILDREN; i++) {
+		SCX_EQ(waitpid(pids[i], &status, 0), pids[i]);
+		SCX_EQ(status, 0);
+	}
+
+	SCX_ASSERT(skel->bss->saw_local);
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct select_cpu_dfl_nodispatch *skel = ctx;
+
+	select_cpu_dfl_nodispatch__destroy(skel);
+}
+
+struct scx_test select_cpu_dfl_nodispatch = {
+	.name = "select_cpu_dfl_nodispatch",
+	.description = "Verify behavior of scx_bpf_select_cpu_dfl() in "
+		       "ops.select_cpu()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&select_cpu_dfl_nodispatch)
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dispatch.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_dispatch.bpf.c
new file mode 100644
index 000000000000..f0b96a4a04b2
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dispatch.bpf.c
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates the behavior of direct dispatching with a default
+ * select_cpu implementation.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+s32 BPF_STRUCT_OPS(select_cpu_dispatch_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	u64 dsq_id = SCX_DSQ_LOCAL;
+	s32 cpu = prev_cpu;
+
+	if (scx_bpf_test_and_clear_cpu_idle(cpu))
+		goto dispatch;
+
+	cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
+	if (cpu >= 0)
+		goto dispatch;
+
+	dsq_id = SCX_DSQ_GLOBAL;
+	cpu = prev_cpu;
+
+dispatch:
+	scx_bpf_dispatch(p, dsq_id, SCX_SLICE_DFL, 0);
+	return cpu;
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops select_cpu_dispatch_ops = {
+	.select_cpu		= select_cpu_dispatch_select_cpu,
+	.name			= "select_cpu_dispatch",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dispatch.c b/tools/testing/selftests/sched_ext/select_cpu_dispatch.c
new file mode 100644
index 000000000000..0309ca8785b3
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dispatch.c
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "select_cpu_dispatch.bpf.skel.h"
+#include "scx_test.h"
+
+#define NUM_CHILDREN 1028
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct select_cpu_dispatch *skel;
+
+	skel = select_cpu_dispatch__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct select_cpu_dispatch *skel = ctx;
+	struct bpf_link *link;
+	pid_t pids[NUM_CHILDREN];
+	int i, status;
+
+	link = bpf_map__attach_struct_ops(skel->maps.select_cpu_dispatch_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	for (i = 0; i < NUM_CHILDREN; i++) {
+		pids[i] = fork();
+		if (pids[i] == 0) {
+			sleep(1);
+			exit(0);
+		}
+	}
+
+	for (i = 0; i < NUM_CHILDREN; i++) {
+		SCX_EQ(waitpid(pids[i], &status, 0), pids[i]);
+		SCX_EQ(status, 0);
+	}
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct select_cpu_dispatch *skel = ctx;
+
+	select_cpu_dispatch__destroy(skel);
+}
+
+struct scx_test select_cpu_dispatch = {
+	.name = "select_cpu_dispatch",
+	.description = "Test direct dispatching to built-in DSQs from "
+		       "ops.select_cpu()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&select_cpu_dispatch)
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.bpf.c
new file mode 100644
index 000000000000..7b42ddce0f56
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.bpf.c
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates the behavior of direct dispatching with a default
+ * select_cpu implementation.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+UEI_DEFINE(uei);
+
+s32 BPF_STRUCT_OPS(select_cpu_dispatch_bad_dsq_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	/* Dispatching to a random DSQ should fail. */
+	scx_bpf_dispatch(p, 0xcafef00d, SCX_SLICE_DFL, 0);
+
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(select_cpu_dispatch_bad_dsq_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops select_cpu_dispatch_bad_dsq_ops = {
+	.select_cpu		= select_cpu_dispatch_bad_dsq_select_cpu,
+	.exit			= select_cpu_dispatch_bad_dsq_exit,
+	.name			= "select_cpu_dispatch_bad_dsq",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.c b/tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.c
new file mode 100644
index 000000000000..47eb6ed7627d
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dispatch_bad_dsq.c
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "select_cpu_dispatch_bad_dsq.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct select_cpu_dispatch_bad_dsq *skel;
+
+	skel = select_cpu_dispatch_bad_dsq__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct select_cpu_dispatch_bad_dsq *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.select_cpu_dispatch_bad_dsq_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_ERROR));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct select_cpu_dispatch_bad_dsq *skel = ctx;
+
+	select_cpu_dispatch_bad_dsq__destroy(skel);
+}
+
+struct scx_test select_cpu_dispatch_bad_dsq = {
+	.name = "select_cpu_dispatch_bad_dsq",
+	.description = "Verify graceful failure if we direct-dispatch to a "
+		       "bogus DSQ in ops.select_cpu()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&select_cpu_dispatch_bad_dsq)
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.bpf.c
new file mode 100644
index 000000000000..653e3dc0b4dc
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.bpf.c
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates the behavior of direct dispatching with a default
+ * select_cpu implementation.
+ *
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+UEI_DEFINE(uei);
+
+s32 BPF_STRUCT_OPS(select_cpu_dispatch_dbl_dsp_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	/* Dispatching twice in a row is disallowed. */
+	scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, 0);
+	scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, 0);
+
+	return prev_cpu;
+}
+
+void BPF_STRUCT_OPS(select_cpu_dispatch_dbl_dsp_exit, struct scx_exit_info *ei)
+{
+	UEI_RECORD(uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops select_cpu_dispatch_dbl_dsp_ops = {
+	.select_cpu		= select_cpu_dispatch_dbl_dsp_select_cpu,
+	.exit			= select_cpu_dispatch_dbl_dsp_exit,
+	.name			= "select_cpu_dispatch_dbl_dsp",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.c b/tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.c
new file mode 100644
index 000000000000..48ff028a3c46
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_dispatch_dbl_dsp.c
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "select_cpu_dispatch_dbl_dsp.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct select_cpu_dispatch_dbl_dsp *skel;
+
+	skel = select_cpu_dispatch_dbl_dsp__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct select_cpu_dispatch_dbl_dsp *skel = ctx;
+	struct bpf_link *link;
+
+	link = bpf_map__attach_struct_ops(skel->maps.select_cpu_dispatch_dbl_dsp_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	sleep(1);
+
+	SCX_EQ(skel->data->uei.kind, EXIT_KIND(SCX_EXIT_ERROR));
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct select_cpu_dispatch_dbl_dsp *skel = ctx;
+
+	select_cpu_dispatch_dbl_dsp__destroy(skel);
+}
+
+struct scx_test select_cpu_dispatch_dbl_dsp = {
+	.name = "select_cpu_dispatch_dbl_dsp",
+	.description = "Verify graceful failure if we dispatch twice to a "
+		       "DSQ in ops.select_cpu()",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&select_cpu_dispatch_dbl_dsp)
diff --git a/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c
new file mode 100644
index 000000000000..7f3ebf4fc2ea
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A scheduler that validates that enqueue flags are properly stored and
+ * applied at dispatch time when a task is directly dispatched from
+ * ops.select_cpu(). We validate this by using scx_bpf_dispatch_vtime(), and
+ * making the test a very basic vtime scheduler.
+ *
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+
+#include <scx/common.bpf.h>
+
+char _license[] SEC("license") = "GPL";
+
+volatile bool consumed;
+
+static u64 vtime_now;
+
+#define VTIME_DSQ 0
+
+static inline bool vtime_before(u64 a, u64 b)
+{
+	return (s64)(a - b) < 0;
+}
+
+static inline u64 task_vtime(const struct task_struct *p)
+{
+	u64 vtime = p->scx.dsq_vtime;
+
+	if (vtime_before(vtime, vtime_now - SCX_SLICE_DFL))
+		return vtime_now - SCX_SLICE_DFL;
+	else
+		return vtime;
+}
+
+s32 BPF_STRUCT_OPS(select_cpu_vtime_select_cpu, struct task_struct *p,
+		   s32 prev_cpu, u64 wake_flags)
+{
+	s32 cpu;
+
+	cpu = scx_bpf_pick_idle_cpu(p->cpus_ptr, 0);
+	if (cpu >= 0)
+		goto ddsp;
+
+	cpu = prev_cpu;
+	scx_bpf_test_and_clear_cpu_idle(cpu);
+ddsp:
+	scx_bpf_dispatch_vtime(p, VTIME_DSQ, SCX_SLICE_DFL, task_vtime(p), 0);
+	return cpu;
+}
+
+void BPF_STRUCT_OPS(select_cpu_vtime_dispatch, s32 cpu, struct task_struct *p)
+{
+	if (scx_bpf_consume(VTIME_DSQ))
+		consumed = true;
+}
+
+void BPF_STRUCT_OPS(select_cpu_vtime_running, struct task_struct *p)
+{
+	if (vtime_before(vtime_now, p->scx.dsq_vtime))
+		vtime_now = p->scx.dsq_vtime;
+}
+
+void BPF_STRUCT_OPS(select_cpu_vtime_stopping, struct task_struct *p,
+		    bool runnable)
+{
+	p->scx.dsq_vtime += (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+}
+
+void BPF_STRUCT_OPS(select_cpu_vtime_enable, struct task_struct *p)
+{
+	p->scx.dsq_vtime = vtime_now;
+}
+
+s32 BPF_STRUCT_OPS_SLEEPABLE(select_cpu_vtime_init)
+{
+	return scx_bpf_create_dsq(VTIME_DSQ, -1);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops select_cpu_vtime_ops = {
+	.select_cpu		= select_cpu_vtime_select_cpu,
+	.dispatch		= select_cpu_vtime_dispatch,
+	.running		= select_cpu_vtime_running,
+	.stopping		= select_cpu_vtime_stopping,
+	.enable			= select_cpu_vtime_enable,
+	.init			= select_cpu_vtime_init,
+	.name			= "select_cpu_vtime",
+	.timeout_ms		= 1000U,
+};
diff --git a/tools/testing/selftests/sched_ext/select_cpu_vtime.c b/tools/testing/selftests/sched_ext/select_cpu_vtime.c
new file mode 100644
index 000000000000..b4629c2364f5
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/select_cpu_vtime.c
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include "select_cpu_vtime.bpf.skel.h"
+#include "scx_test.h"
+
+static enum scx_test_status setup(void **ctx)
+{
+	struct select_cpu_vtime *skel;
+
+	skel = select_cpu_vtime__open_and_load();
+	SCX_FAIL_IF(!skel, "Failed to open and load skel");
+	*ctx = skel;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	struct select_cpu_vtime *skel = ctx;
+	struct bpf_link *link;
+
+	SCX_ASSERT(!skel->bss->consumed);
+
+	link = bpf_map__attach_struct_ops(skel->maps.select_cpu_vtime_ops);
+	SCX_FAIL_IF(!link, "Failed to attach scheduler");
+
+	sleep(1);
+
+	SCX_ASSERT(skel->bss->consumed);
+
+	bpf_link__destroy(link);
+
+	return SCX_TEST_PASS;
+}
+
+static void cleanup(void *ctx)
+{
+	struct select_cpu_vtime *skel = ctx;
+
+	select_cpu_vtime__destroy(skel);
+}
+
+struct scx_test select_cpu_vtime = {
+	.name = "select_cpu_vtime",
+	.description = "Test doing direct vtime-dispatching from "
+		       "ops.select_cpu(), to a non-built-in DSQ",
+	.setup = setup,
+	.run = run,
+	.cleanup = cleanup,
+};
+REGISTER_SCX_TEST(&select_cpu_vtime)
diff --git a/tools/testing/selftests/sched_ext/test_example.c b/tools/testing/selftests/sched_ext/test_example.c
new file mode 100644
index 000000000000..ce36cdf03cdc
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/test_example.c
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <bpf/bpf.h>
+#include <scx/common.h>
+#include "scx_test.h"
+
+static bool setup_called = false;
+static bool run_called = false;
+static bool cleanup_called = false;
+
+static int context = 10;
+
+static enum scx_test_status setup(void **ctx)
+{
+	setup_called = true;
+	*ctx = &context;
+
+	return SCX_TEST_PASS;
+}
+
+static enum scx_test_status run(void *ctx)
+{
+	int *arg = ctx;
+
+	SCX_ASSERT(setup_called);
+	SCX_ASSERT(!run_called && !cleanup_called);
+	SCX_EQ(*arg, context);
+
+	run_called = true;
+	return SCX_TEST_PASS;
+}
+
+static void cleanup (void *ctx)
+{
+	SCX_BUG_ON(!run_called || cleanup_called, "Wrong callbacks invoked");
+}
+
+struct scx_test example = {
+	.name		= "example",
+	.description	= "Validate the basic function of the test suite itself",
+	.setup		= setup,
+	.run		= run,
+	.cleanup	= cleanup,
+};
+REGISTER_SCX_TEST(&example)
diff --git a/tools/testing/selftests/sched_ext/util.c b/tools/testing/selftests/sched_ext/util.c
new file mode 100644
index 000000000000..e47769c91918
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/util.c
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <dvernet@meta.com>
+ */
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+/* Returns read len on success, or -errno on failure. */
+static ssize_t read_text(const char *path, char *buf, size_t max_len)
+{
+	ssize_t len;
+	int fd;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	len = read(fd, buf, max_len - 1);
+
+	if (len >= 0)
+		buf[len] = 0;
+
+	close(fd);
+	return len < 0 ? -errno : len;
+}
+
+/* Returns written len on success, or -errno on failure. */
+static ssize_t write_text(const char *path, char *buf, ssize_t len)
+{
+	int fd;
+	ssize_t written;
+
+	fd = open(path, O_WRONLY | O_APPEND);
+	if (fd < 0)
+		return -errno;
+
+	written = write(fd, buf, len);
+	close(fd);
+	return written < 0 ? -errno : written;
+}
+
+long file_read_long(const char *path)
+{
+	char buf[128];
+
+
+	if (read_text(path, buf, sizeof(buf)) <= 0)
+		return -1;
+
+	return atol(buf);
+}
+
+int file_write_long(const char *path, long val)
+{
+	char buf[64];
+	int ret;
+
+	ret = sprintf(buf, "%lu", val);
+	if (ret < 0)
+		return ret;
+
+	if (write_text(path, buf, sizeof(buf)) <= 0)
+		return -1;
+
+	return 0;
+}
diff --git a/tools/testing/selftests/sched_ext/util.h b/tools/testing/selftests/sched_ext/util.h
new file mode 100644
index 000000000000..bc13dfec1267
--- /dev/null
+++ b/tools/testing/selftests/sched_ext/util.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2024 David Vernet <void@manifault.com>
+ */
+
+#ifndef __SCX_TEST_UTIL_H__
+#define __SCX_TEST_UTIL_H__
+
+long file_read_long(const char *path);
+int file_write_long(const char *path, long val);
+
+#endif // __SCX_TEST_H__