path: root/SOURCES/tkg-BBRv2.patch

From eff7e1edf2fec63bac1a81f8c86295dd3f48422a Mon Sep 17 00:00:00 2001
From: Oleksandr Natalenko <oleksandr@natalenko.name>
Date: Mon, 4 Apr 2022 08:23:19 +0200
Subject: [PATCH] tcp_bbr2: introduce BBRv2

Signed-off-by: Oleksandr Natalenko <oleksandr@natalenko.name>
---
 include/linux/tcp.h                |    3 +-
 include/net/inet_connection_sock.h |    3 +-
 include/net/tcp.h                  |   41 +-
 include/uapi/linux/inet_diag.h     |   33 +
 net/ipv4/Kconfig                   |   22 +
 net/ipv4/Makefile                  |    1 +
 net/ipv4/tcp.c                     |    1 +
 net/ipv4/tcp_bbr.c                 |   38 +-
 net/ipv4/tcp_bbr2.c                | 2674 ++++++++++++++++++++++++++++
 net/ipv4/tcp_cong.c                |    1 +
 net/ipv4/tcp_input.c               |   27 +-
 net/ipv4/tcp_output.c              |   26 +-
 net/ipv4/tcp_rate.c                |   30 +-
 net/ipv4/tcp_timer.c               |    1 +
 14 files changed, 2867 insertions(+), 34 deletions(-)
 create mode 100644 net/ipv4/tcp_bbr2.c

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 41b1da621a45..d8f94ef1a297 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -255,7 +255,8 @@ struct tcp_sock {
 	u8	compressed_ack;
 	u8	dup_ack_counter:2,
 		tlp_retrans:1,	/* TLP is a retransmission */
-		unused:5;
+		fast_ack_mode:2, /* which fast ack mode ? */
+		unused:3;
 	u32	chrono_start;	/* Start time in jiffies of a TCP chrono */
 	u32	chrono_stat[3];	/* Time in jiffies for chrono_stat stats */
 	u8	chrono_type:2,	/* current chronograph type */
diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index c2b15f7e5516..d85858efa571 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -135,7 +135,8 @@ struct inet_connection_sock {
 	u32			  icsk_probes_tstamp;
 	u32			  icsk_user_timeout;
 
-	u64			  icsk_ca_priv[104 / sizeof(u64)];
+/* XXX inflated by temporary internal debugging info */
+	u64			  icsk_ca_priv[216 / sizeof(u64)];
 #define ICSK_CA_PRIV_SIZE	  sizeof_field(struct inet_connection_sock, icsk_ca_priv)
 };
 
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 14d45661a84d..7261fae79403 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -375,6 +375,7 @@ static inline void tcp_dec_quickack_mode(struct sock *sk,
 #define	TCP_ECN_QUEUE_CWR	2
 #define	TCP_ECN_DEMAND_CWR	4
 #define	TCP_ECN_SEEN		8
+#define	TCP_ECN_ECT_PERMANENT	16
 
 enum tcp_tw_status {
 	TCP_TW_SUCCESS = 0,
@@ -823,6 +824,11 @@ static inline u32 tcp_stamp_us_delta(u64 t1, u64 t0)
 	return max_t(s64, t1 - t0, 0);
 }
 
+static inline u32 tcp_stamp32_us_delta(u32 t1, u32 t0)
+{
+	return max_t(s32, t1 - t0, 0);
+}
+
 static inline u32 tcp_skb_timestamp(const struct sk_buff *skb)
 {
 	return tcp_ns_to_ts(skb->skb_mstamp_ns);
@@ -898,9 +904,14 @@ struct tcp_skb_cb {
 			/* pkts S/ACKed so far upon tx of skb, incl retrans: */
 			__u32 delivered;
 			/* start of send pipeline phase */
-			u64 first_tx_mstamp;
+			u32 first_tx_mstamp;
 			/* when we reached the "delivered" count */
-			u64 delivered_mstamp;
+			u32 delivered_mstamp;
+#define TCPCB_IN_FLIGHT_BITS 20
+#define TCPCB_IN_FLIGHT_MAX ((1U << TCPCB_IN_FLIGHT_BITS) - 1)
+			u32 in_flight:20,   /* packets in flight at transmit */
+			    unused2:12;
+			u32 lost;	/* packets lost so far upon tx of skb */
 		} tx;   /* only used for outgoing skbs */
 		union {
 			struct inet_skb_parm	h4;
@@ -1026,7 +1037,11 @@ enum tcp_ca_ack_event_flags {
 #define TCP_CONG_NON_RESTRICTED 0x1
 /* Requires ECN/ECT set on all packets */
 #define TCP_CONG_NEEDS_ECN	0x2
-#define TCP_CONG_MASK	(TCP_CONG_NON_RESTRICTED | TCP_CONG_NEEDS_ECN)
+/* Wants notification of CE events (CA_EVENT_ECN_IS_CE, CA_EVENT_ECN_NO_CE). */
+#define TCP_CONG_WANTS_CE_EVENTS	0x4
+#define TCP_CONG_MASK	(TCP_CONG_NON_RESTRICTED | \
+			 TCP_CONG_NEEDS_ECN | \
+			 TCP_CONG_WANTS_CE_EVENTS)
 
 union tcp_cc_info;
 
@@ -1046,8 +1061,11 @@ struct ack_sample {
  */
 struct rate_sample {
 	u64  prior_mstamp; /* starting timestamp for interval */
+	u32  prior_lost;	/* tp->lost at "prior_mstamp" */
 	u32  prior_delivered;	/* tp->delivered at "prior_mstamp" */
 	u32  prior_delivered_ce;/* tp->delivered_ce at "prior_mstamp" */
+	u32 tx_in_flight;	/* packets in flight at starting timestamp */
+	s32  lost;		/* number of packets lost over interval */
 	s32  delivered;		/* number of packets delivered over interval */
 	s32  delivered_ce;	/* number of packets delivered w/ CE marks*/
 	long interval_us;	/* time for tp->delivered to incr "delivered" */
@@ -1061,6 +1079,7 @@ struct rate_sample {
 	bool is_app_limited;	/* is sample from packet with bubble in pipe? */
 	bool is_retrans;	/* is sample from retransmission? */
 	bool is_ack_delayed;	/* is this (likely) a delayed ACK? */
+	bool is_ece;		/* did this ACK have ECN marked? */
 };
 
 struct tcp_congestion_ops {
@@ -1084,8 +1103,11 @@ struct tcp_congestion_ops {
 	/* hook for packet ack accounting (optional) */
 	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
 
-	/* override sysctl_tcp_min_tso_segs */
-	u32 (*min_tso_segs)(struct sock *sk);
+	/* pick target number of segments per TSO/GSO skb (optional): */
+	u32 (*tso_segs)(struct sock *sk, unsigned int mss_now);
+
+	/* react to a specific lost skb (optional) */
+	void (*skb_marked_lost)(struct sock *sk, const struct sk_buff *skb);
 
 	/* call when packets are delivered to update cwnd and pacing rate,
 	 * after all the ca_state processing. (optional)
@@ -1148,6 +1170,14 @@ static inline char *tcp_ca_get_name_by_key(u32 key, char *buffer)
 }
 #endif
 
+static inline bool tcp_ca_wants_ce_events(const struct sock *sk)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+
+	return icsk->icsk_ca_ops->flags & (TCP_CONG_NEEDS_ECN |
+					   TCP_CONG_WANTS_CE_EVENTS);
+}
+
 static inline bool tcp_ca_needs_ecn(const struct sock *sk)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -1167,6 +1197,7 @@ static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
 void tcp_set_ca_state(struct sock *sk, const u8 ca_state);
 
 /* From tcp_rate.c */
+void tcp_set_tx_in_flight(struct sock *sk, struct sk_buff *skb);
 void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb);
 void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 			    struct rate_sample *rs);
diff --git a/include/uapi/linux/inet_diag.h b/include/uapi/linux/inet_diag.h
index 50655de04c9b..0e24f11627d5 100644
--- a/include/uapi/linux/inet_diag.h
+++ b/include/uapi/linux/inet_diag.h
@@ -231,9 +231,42 @@ struct tcp_bbr_info {
 	__u32	bbr_cwnd_gain;		/* cwnd gain shifted left 8 bits */
 };
 
+/* Phase as reported in netlink/ss stats. */
+enum tcp_bbr2_phase {
+	BBR2_PHASE_INVALID		= 0,
+	BBR2_PHASE_STARTUP		= 1,
+	BBR2_PHASE_DRAIN		= 2,
+	BBR2_PHASE_PROBE_RTT		= 3,
+	BBR2_PHASE_PROBE_BW_UP		= 4,
+	BBR2_PHASE_PROBE_BW_DOWN	= 5,
+	BBR2_PHASE_PROBE_BW_CRUISE	= 6,
+	BBR2_PHASE_PROBE_BW_REFILL	= 7
+};
+
+struct tcp_bbr2_info {
+	/* u64 bw: bandwidth (app throughput) estimate in Byte per sec: */
+	__u32	bbr_bw_lsb;		/* lower 32 bits of bw */
+	__u32	bbr_bw_msb;		/* upper 32 bits of bw */
+	__u32	bbr_min_rtt;		/* min-filtered RTT in uSec */
+	__u32	bbr_pacing_gain;	/* pacing gain shifted left 8 bits */
+	__u32	bbr_cwnd_gain;		/* cwnd gain shifted left 8 bits */
+	__u32	bbr_bw_hi_lsb;		/* lower 32 bits of bw_hi */
+	__u32	bbr_bw_hi_msb;		/* upper 32 bits of bw_hi */
+	__u32	bbr_bw_lo_lsb;		/* lower 32 bits of bw_lo */
+	__u32	bbr_bw_lo_msb;		/* upper 32 bits of bw_lo */
+	__u8	bbr_mode;		/* current bbr_mode in state machine */
+	__u8	bbr_phase;		/* current state machine phase */
+	__u8	unused1;		/* alignment padding; not used yet */
+	__u8	bbr_version;		/* MUST be at this offset in struct */
+	__u32	bbr_inflight_lo;	/* lower/short-term data volume bound */
+	__u32	bbr_inflight_hi;	/* higher/long-term data volume bound */
+	__u32	bbr_extra_acked;	/* max excess packets ACKed in epoch */
+};
+
 union tcp_cc_info {
 	struct tcpvegas_info	vegas;
 	struct tcp_dctcp_info	dctcp;
 	struct tcp_bbr_info	bbr;
+	struct tcp_bbr2_info	bbr2;
 };
 #endif /* _UAPI_INET_DIAG_H_ */
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 2dfb12230f08..b6bec331a82e 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -678,6 +678,24 @@ config TCP_CONG_BBR
 	  AQM schemes that do not provide a delay signal. It requires the fq
 	  ("Fair Queue") pacing packet scheduler.
 
+config TCP_CONG_BBR2
+	tristate "BBR2 TCP"
+	default n
+	help
+
+	BBR2 TCP congestion control is a model-based congestion control
+	algorithm that aims to maximize network utilization, keep queues and
+	retransmit rates low, and to be able to coexist with Reno/CUBIC in
+	common scenarios. It builds an explicit model of the network path.  It
+	tolerates a targeted degree of random packet loss and delay that are
+	unrelated to congestion. It can operate over LAN, WAN, cellular, wifi,
+	or cable modem links, and can use DCTCP-L4S-style ECN signals.  It can
+	coexist with flows that use loss-based congestion control, and can
+	operate with shallow buffers, deep buffers, bufferbloat, policers, or
+	AQM schemes that do not provide a delay signal. It requires pacing,
+	using either TCP internal pacing or the fq ("Fair Queue") pacing packet
+	scheduler.
+
 choice
 	prompt "Default TCP congestion control"
 	default DEFAULT_CUBIC
@@ -715,6 +733,9 @@ choice
 	config DEFAULT_BBR
 		bool "BBR" if TCP_CONG_BBR=y
 
+	config DEFAULT_BBR2
+		bool "BBR2" if TCP_CONG_BBR2=y
+
 	config DEFAULT_RENO
 		bool "Reno"
 endchoice
@@ -739,6 +760,7 @@ config DEFAULT_TCP_CONG
 	default "dctcp" if DEFAULT_DCTCP
 	default "cdg" if DEFAULT_CDG
 	default "bbr" if DEFAULT_BBR
+	default "bbr2" if DEFAULT_BBR2
 	default "cubic"
 
 config TCP_MD5SIG
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index bbdd9c44f14e..8dee1547d820 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -46,6 +46,7 @@ obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
 obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o
 obj-$(CONFIG_INET_RAW_DIAG) += raw_diag.o
 obj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o
+obj-$(CONFIG_TCP_CONG_BBR2) += tcp_bbr2.o
 obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 obj-$(CONFIG_TCP_CONG_CDG) += tcp_cdg.o
 obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 4f2205756cfe..c139747666dd 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3188,6 +3188,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tp->rx_opt.dsack = 0;
 	tp->rx_opt.num_sacks = 0;
 	tp->rcv_ooopack = 0;
+	tp->fast_ack_mode = 0;
 
 
 	/* Clean up fastopen related fields */
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 54eec33c6e1c..bfbf158c71f4 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -294,26 +294,40 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
 		sk->sk_pacing_rate = rate;
 }
 
-/* override sysctl_tcp_min_tso_segs */
 __bpf_kfunc static u32 bbr_min_tso_segs(struct sock *sk)
 {
 	return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
 }
 
+/* Return the number of segments BBR would like in a TSO/GSO skb, given
+ * a particular max gso size as a constraint.
+ */
+static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now,
+				u32 gso_max_size)
+{
+	u32 segs;
+	u64 bytes;
+
+	/* Budget a TSO/GSO burst size allowance based on bw (pacing_rate). */
+	bytes = sk->sk_pacing_rate >> sk->sk_pacing_shift;
+
+	bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
+	segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk));
+	return segs;
+}
+
+/* Custom tcp_tso_autosize() for BBR, used at transmit time to cap skb size. */
+static u32  bbr_tso_segs(struct sock *sk, unsigned int mss_now)
+{
+	return bbr_tso_segs_generic(sk, mss_now, sk->sk_gso_max_size);
+}
+
+/* Like bbr_tso_segs(), using mss_cache, ignoring driver's sk_gso_max_size. */
 static u32 bbr_tso_segs_goal(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	u32 segs, bytes;
-
-	/* Sort of tcp_tso_autosize() but ignoring
-	 * driver provided sk_gso_max_size.
-	 */
-	bytes = min_t(unsigned long,
-		      sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift),
-		      GSO_LEGACY_MAX_SIZE - 1 - MAX_TCP_HEADER);
-	segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk));
 
-	return min(segs, 0x7FU);
+	return  bbr_tso_segs_generic(sk, tp->mss_cache, GSO_LEGACY_MAX_SIZE);
 }
 
 /* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
@@ -1149,7 +1163,7 @@ static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
 	.undo_cwnd	= bbr_undo_cwnd,
 	.cwnd_event	= bbr_cwnd_event,
 	.ssthresh	= bbr_ssthresh,
-	.min_tso_segs	= bbr_min_tso_segs,
+	.tso_segs	= bbr_tso_segs,
 	.get_info	= bbr_get_info,
 	.set_state	= bbr_set_state,
 };
diff --git a/net/ipv4/tcp_bbr2.c b/net/ipv4/tcp_bbr2.c
new file mode 100644
index 000000000000..488429f0f3d0
--- /dev/null
+++ b/net/ipv4/tcp_bbr2.c
@@ -0,0 +1,2674 @@
+/* BBR (Bottleneck Bandwidth and RTT) congestion control, v2
+ *
+ * BBRv2 is a model-based congestion control algorithm that aims for low
+ * queues, low loss, and (bounded) Reno/CUBIC coexistence. To maintain a model
+ * of the network path, it uses measurements of bandwidth and RTT, as well as
+ * (if they occur) packet loss and/or DCTCP/L4S-style ECN signals.  Note that
+ * although it can use ECN or loss signals explicitly, it does not require
+ * either; it can bound its in-flight data based on its estimate of the BDP.
+ *
+ * The model has both higher and lower bounds for the operating range:
+ *   lo: bw_lo, inflight_lo: conservative short-term lower bound
+ *   hi: bw_hi, inflight_hi: robust long-term upper bound
+ * The bandwidth-probing time scale is (a) extended dynamically based on
+ * estimated BDP to improve coexistence with Reno/CUBIC; (b) bounded by
+ * an interactive wall-clock time-scale to be more scalable and responsive
+ * than Reno and CUBIC.
+ *
+ * Here is a state transition diagram for BBR:
+ *
+ *             |
+ *             V
+ *    +---> STARTUP  ----+
+ *    |        |         |
+ *    |        V         |
+ *    |      DRAIN   ----+
+ *    |        |         |
+ *    |        V         |
+ *    +---> PROBE_BW ----+
+ *    |      ^    |      |
+ *    |      |    |      |
+ *    |      +----+      |
+ *    |                  |
+ *    +---- PROBE_RTT <--+
+ *
+ * A BBR flow starts in STARTUP, and ramps up its sending rate quickly.
+ * When it estimates the pipe is full, it enters DRAIN to drain the queue.
+ * In steady state a BBR flow only uses PROBE_BW and PROBE_RTT.
+ * A long-lived BBR flow spends the vast majority of its time remaining
+ * (repeatedly) in PROBE_BW, fully probing and utilizing the pipe's bandwidth
+ * in a fair manner, with a small, bounded queue. *If* a flow has been
+ * continuously sending for the entire min_rtt window, and hasn't seen an RTT
+ * sample that matches or decreases its min_rtt estimate for 10 seconds, then
+ * it briefly enters PROBE_RTT to cut inflight to a minimum value to re-probe
+ * the path's two-way propagation delay (min_rtt). When exiting PROBE_RTT, if
+ * we estimated that we reached the full bw of the pipe then we enter PROBE_BW;
+ * otherwise we enter STARTUP to try to fill the pipe.
+ *
+ * BBR is described in detail in:
+ *   "BBR: Congestion-Based Congestion Control",
+ *   Neal Cardwell, Yuchung Cheng, C. Stephen Gunn, Soheil Hassas Yeganeh,
+ *   Van Jacobson. ACM Queue, Vol. 14 No. 5, September-October 2016.
+ *
+ * There is a public e-mail list for discussing BBR development and testing:
+ *   https://groups.google.com/forum/#!forum/bbr-dev
+ *
+ * NOTE: BBR might be used with the fq qdisc ("man tc-fq") with pacing enabled,
+ * otherwise TCP stack falls back to an internal pacing using one high
+ * resolution timer per TCP socket and may use more resources.
+ */
+#include <linux/module.h>
+#include <net/tcp.h>
+#include <linux/inet_diag.h>
+#include <linux/inet.h>
+#include <linux/random.h>
+
+#include "tcp_dctcp.h"
+
+/* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth
+ * estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps.
+ * This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32.
+ * Since the minimum window is >=4 packets, the lower bound isn't
+ * an issue. The upper bound isn't an issue with existing technologies.
+ */
+#define BW_SCALE 24
+#define BW_UNIT (1 << BW_SCALE)
+
+#define BBR_SCALE 8	/* scaling factor for fractions in BBR (e.g. gains) */
+#define BBR_UNIT (1 << BBR_SCALE)
+
+#define FLAG_DEBUG_VERBOSE	0x1	/* Verbose debugging messages */
+#define FLAG_DEBUG_LOOPBACK	0x2	/* Do NOT skip loopback addr */
+
+#define CYCLE_LEN		8	/* number of phases in a pacing gain cycle */
+
+/* BBR has the following modes for deciding how fast to send: */
+enum bbr_mode {
+	BBR_STARTUP,	/* ramp up sending rate rapidly to fill pipe */
+	BBR_DRAIN,	/* drain any queue created during startup */
+	BBR_PROBE_BW,	/* discover, share bw: pace around estimated bw */
+	BBR_PROBE_RTT,	/* cut inflight to min to probe min_rtt */
+};
+
+/* How does the incoming ACK stream relate to our bandwidth probing? */
+enum bbr_ack_phase {
+	BBR_ACKS_INIT,		  /* not probing; not getting probe feedback */
+	BBR_ACKS_REFILLING,	  /* sending at est. bw to fill pipe */
+	BBR_ACKS_PROBE_STARTING,  /* inflight rising to probe bw */
+	BBR_ACKS_PROBE_FEEDBACK,  /* getting feedback from bw probing */
+	BBR_ACKS_PROBE_STOPPING,  /* stopped probing; still getting feedback */
+};
+
+/* BBR congestion control block */
+struct bbr {
+	u32	min_rtt_us;	        /* min RTT in min_rtt_win_sec window */
+	u32	min_rtt_stamp;	        /* timestamp of min_rtt_us */
+	u32	probe_rtt_done_stamp;   /* end time for BBR_PROBE_RTT mode */
+	u32	probe_rtt_min_us;	/* min RTT in bbr_probe_rtt_win_ms window */
+	u32	probe_rtt_min_stamp;	/* timestamp of probe_rtt_min_us*/
+	u32     next_rtt_delivered; /* scb->tx.delivered at end of round */
+	u32	prior_rcv_nxt;	/* tp->rcv_nxt when CE state last changed */
+	u64	cycle_mstamp;	     /* time of this cycle phase start */
+	u32     mode:3,		     /* current bbr_mode in state machine */
+		prev_ca_state:3,     /* CA state on previous ACK */
+		packet_conservation:1,  /* use packet conservation? */
+		round_start:1,	     /* start of packet-timed tx->ack round? */
+		ce_state:1,          /* If most recent data has CE bit set */
+		bw_probe_up_rounds:5,   /* cwnd-limited rounds in PROBE_UP */
+		try_fast_path:1, 	/* can we take fast path? */
+		unused2:11,
+		idle_restart:1,	     /* restarting after idle? */
+		probe_rtt_round_done:1,  /* a BBR_PROBE_RTT round at 4 pkts? */
+		cycle_idx:3,	/* current index in pacing_gain cycle array */
+		has_seen_rtt:1;	     /* have we seen an RTT sample yet? */
+	u32	pacing_gain:11,	/* current gain for setting pacing rate */
+		cwnd_gain:11,	/* current gain for setting cwnd */
+		full_bw_reached:1,   /* reached full bw in Startup? */
+		full_bw_cnt:2,	/* number of rounds without large bw gains */
+		init_cwnd:7;	/* initial cwnd */
+	u32	prior_cwnd;	/* prior cwnd upon entering loss recovery */
+	u32	full_bw;	/* recent bw, to estimate if pipe is full */
+
+	/* For tracking ACK aggregation: */
+	u64	ack_epoch_mstamp;	/* start of ACK sampling epoch */
+	u16	extra_acked[2];		/* max excess data ACKed in epoch */
+	u32	ack_epoch_acked:20,	/* packets (S)ACKed in sampling epoch */
+		extra_acked_win_rtts:5,	/* age of extra_acked, in round trips */
+		extra_acked_win_idx:1,	/* current index in extra_acked array */
+	/* BBR v2 state: */
+		unused1:2,
+		startup_ecn_rounds:2,	/* consecutive hi ECN STARTUP rounds */
+		loss_in_cycle:1,	/* packet loss in this cycle? */
+		ecn_in_cycle:1;		/* ECN in this cycle? */
+	u32	loss_round_delivered; /* scb->tx.delivered ending loss round */
+	u32	undo_bw_lo;	     /* bw_lo before latest losses */
+	u32	undo_inflight_lo;    /* inflight_lo before latest losses */
+	u32	undo_inflight_hi;    /* inflight_hi before latest losses */
+	u32	bw_latest;	 /* max delivered bw in last round trip */
+	u32	bw_lo;		 /* lower bound on sending bandwidth */
+	u32	bw_hi[2];	 /* upper bound of sending bandwidth range*/
+	u32	inflight_latest; /* max delivered data in last round trip */
+	u32	inflight_lo;	 /* lower bound of inflight data range */
+	u32	inflight_hi;	 /* upper bound of inflight data range */
+	u32	bw_probe_up_cnt; /* packets delivered per inflight_hi incr */
+	u32	bw_probe_up_acks;  /* packets (S)ACKed since inflight_hi incr */
+	u32	probe_wait_us;	 /* PROBE_DOWN until next clock-driven probe */
+	u32	ecn_eligible:1,	/* sender can use ECN (RTT, handshake)? */
+		ecn_alpha:9,	/* EWMA delivered_ce/delivered; 0..256 */
+		bw_probe_samples:1,    /* rate samples reflect bw probing? */
+		prev_probe_too_high:1, /* did last PROBE_UP go too high? */
+		stopped_risky_probe:1, /* last PROBE_UP stopped due to risk? */
+		rounds_since_probe:8,  /* packet-timed rounds since probed bw */
+		loss_round_start:1,    /* loss_round_delivered round trip? */
+		loss_in_round:1,       /* loss marked in this round trip? */
+		ecn_in_round:1,	       /* ECN marked in this round trip? */
+		ack_phase:3,	       /* bbr_ack_phase: meaning of ACKs */
+		loss_events_in_round:4,/* losses in STARTUP round */
+		initialized:1;	       /* has bbr_init() been called? */
+	u32	alpha_last_delivered;	 /* tp->delivered    at alpha update */
+	u32	alpha_last_delivered_ce; /* tp->delivered_ce at alpha update */
+
+	/* Params configurable using setsockopt. Refer to correspoding
+	 * module param for detailed description of params.
+	 */
+	struct bbr_params {
+		u32	high_gain:11,		/* max allowed value: 2047 */
+			drain_gain:10,		/* max allowed value: 1023 */
+			cwnd_gain:11;		/* max allowed value: 2047 */
+		u32	cwnd_min_target:4,	/* max allowed value: 15 */
+			min_rtt_win_sec:5,	/* max allowed value: 31 */
+			probe_rtt_mode_ms:9,	/* max allowed value: 511 */
+			full_bw_cnt:3,		/* max allowed value: 7 */
+			cwnd_tso_budget:1,	/* allowed values: {0, 1} */
+			unused3:6,
+			drain_to_target:1,	/* boolean */
+			precise_ece_ack:1,	/* boolean */
+			extra_acked_in_startup:1, /* allowed values: {0, 1} */
+			fast_path:1;		/* boolean */
+		u32	full_bw_thresh:10,	/* max allowed value: 1023 */
+			startup_cwnd_gain:11,	/* max allowed value: 2047 */
+			bw_probe_pif_gain:9,	/* max allowed value: 511 */
+			usage_based_cwnd:1, 	/* boolean */
+			unused2:1;
+		u16	probe_rtt_win_ms:14,	/* max allowed value: 16383 */
+			refill_add_inc:2;	/* max allowed value: 3 */
+		u16	extra_acked_gain:11,	/* max allowed value: 2047 */
+			extra_acked_win_rtts:5; /* max allowed value: 31*/
+		u16	pacing_gain[CYCLE_LEN]; /* max allowed value: 1023 */
+		/* Mostly BBR v2 parameters below here: */
+		u32	ecn_alpha_gain:8,	/* max allowed value: 255 */
+			ecn_factor:8,		/* max allowed value: 255 */
+			ecn_thresh:8,		/* max allowed value: 255 */
+			beta:8;			/* max allowed value: 255 */
+		u32	ecn_max_rtt_us:19,	/* max allowed value: 524287 */
+			bw_probe_reno_gain:9,	/* max allowed value: 511 */
+			full_loss_cnt:4;	/* max allowed value: 15 */
+		u32	probe_rtt_cwnd_gain:8,	/* max allowed value: 255 */
+			inflight_headroom:8,	/* max allowed value: 255 */
+			loss_thresh:8,		/* max allowed value: 255 */
+			bw_probe_max_rounds:8;	/* max allowed value: 255 */
+		u32	bw_probe_rand_rounds:4, /* max allowed value: 15 */
+			bw_probe_base_us:26,	/* usecs: 0..2^26-1 (67 secs) */
+			full_ecn_cnt:2;		/* max allowed value: 3 */
+		u32	bw_probe_rand_us:26,	/* usecs: 0..2^26-1 (67 secs) */
+			undo:1,			/* boolean */
+			tso_rtt_shift:4,	/* max allowed value: 15 */
+			unused5:1;
+		u32	ecn_reprobe_gain:9,	/* max allowed value: 511 */
+			unused1:14,
+			ecn_alpha_init:9;	/* max allowed value: 256 */
+	} params;
+
+	struct {
+		u32	snd_isn; /* Initial sequence number */
+		u32	rs_bw; 	 /* last valid rate sample bw */
+		u32	target_cwnd; /* target cwnd, based on BDP */
+		u8	undo:1,  /* Undo even happened but not yet logged */
+			unused:7;
+		char	event;	 /* single-letter event debug codes */
+		u16	unused2;
+	} debug;
+};
+
+struct bbr_context {
+	u32 sample_bw;
+	u32 target_cwnd;
+	u32 log:1;
+};
+
+/* Window length of min_rtt filter (in sec). Max allowed value is 31 (0x1F) */
+static u32 bbr_min_rtt_win_sec = 10;
+/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode.
+ * Max allowed value is 511 (0x1FF).
+ */
+static u32 bbr_probe_rtt_mode_ms = 200;
+/* Window length of probe_rtt_min_us filter (in ms), and consequently the
+ * typical interval between PROBE_RTT mode entries.
+ * Note that bbr_probe_rtt_win_ms must be <= bbr_min_rtt_win_sec * MSEC_PER_SEC
+ */
+static u32 bbr_probe_rtt_win_ms = 5000;
+/* Skip TSO below the following bandwidth (bits/sec): */
+static int bbr_min_tso_rate = 1200000;
+
+/* Use min_rtt to help adapt TSO burst size, with smaller min_rtt resulting
+ * in bigger TSO bursts. By default we cut the RTT-based allowance in half
+ * for every 2^9 usec (aka 512 us) of RTT, so that the RTT-based allowance
+ * is below 1500 bytes after 6 * ~500 usec = 3ms.
+ */
+static u32 bbr_tso_rtt_shift = 9;  /* halve allowance per 2^9 usecs, 512us */
+
+/* Select cwnd TSO budget approach:
+ *  0: padding
+ *  1: flooring
+ */
+static uint bbr_cwnd_tso_budget = 1;
+
+/* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck.
+ * In order to help drive the network toward lower queues and low latency while
+ * maintaining high utilization, the average pacing rate aims to be slightly
+ * lower than the estimated bandwidth. This is an important aspect of the
+ * design.
+ */
+static const int bbr_pacing_margin_percent = 1;
+
+/* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain
+ * that will allow a smoothly increasing pacing rate that will double each RTT
+ * and send the same number of packets per RTT that an un-paced, slow-starting
+ * Reno or CUBIC flow would. Max allowed value is 2047 (0x7FF).
+ */
+static int bbr_high_gain  = BBR_UNIT * 2885 / 1000 + 1;
+/* The gain for deriving startup cwnd. Max allowed value is 2047 (0x7FF). */
+static int bbr_startup_cwnd_gain  = BBR_UNIT * 2885 / 1000 + 1;
+/* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain
+ * the queue created in BBR_STARTUP in a single round. Max allowed value
+ * is 1023 (0x3FF).
+ */
+static int bbr_drain_gain = BBR_UNIT * 1000 / 2885;
+/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs.
+ * Max allowed value is 2047 (0x7FF).
+ */
+static int bbr_cwnd_gain  = BBR_UNIT * 2;
+/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw.
+ * Max allowed value for each element is 1023 (0x3FF).
+ */
+enum bbr_pacing_gain_phase {
+	BBR_BW_PROBE_UP		= 0,  /* push up inflight to probe for bw/vol */
+	BBR_BW_PROBE_DOWN	= 1,  /* drain excess inflight from the queue */
+	BBR_BW_PROBE_CRUISE	= 2,  /* use pipe, w/ headroom in queue/pipe */
+	BBR_BW_PROBE_REFILL	= 3,  /* v2: refill the pipe again to 100% */
+};
+static int bbr_pacing_gain[] = {
+	BBR_UNIT * 5 / 4,	/* probe for more available bw */
+	BBR_UNIT * 3 / 4,	/* drain queue and/or yield bw to other flows */
+	BBR_UNIT, BBR_UNIT, BBR_UNIT,	/* cruise at 1.0*bw to utilize pipe, */
+	BBR_UNIT, BBR_UNIT, BBR_UNIT	/* without creating excess queue... */
+};
+
+/* Try to keep at least this many packets in flight, if things go smoothly. For
+ * smooth functioning, a sliding window protocol ACKing every other packet
+ * needs at least 4 packets in flight. Max allowed value is 15 (0xF).
+ */
+static u32 bbr_cwnd_min_target = 4;
+
+/* Cwnd to BDP proportion in PROBE_RTT mode scaled by BBR_UNIT. Default: 50%.
+ * Use 0 to disable. Max allowed value is 255.
+ */
+static u32 bbr_probe_rtt_cwnd_gain = BBR_UNIT * 1 / 2;
+
+/* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */
+/* If bw has increased significantly (1.25x), there may be more bw available.
+ * Max allowed value is 1023 (0x3FF).
+ */
+static u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4;
+/* But after 3 rounds w/o significant bw growth, estimate pipe is full.
+ * Max allowed value is 7 (0x7).
+ */
+static u32 bbr_full_bw_cnt = 3;
+
+static u32 bbr_flags;		/* Debugging related stuff */
+
+/* Whether to debug using printk.
+ */
+static bool bbr_debug_with_printk;
+
+/* Whether to debug using ftrace event tcp:tcp_bbr_event.
+ * Ignored when bbr_debug_with_printk is set.
+ */
+static bool bbr_debug_ftrace;
+
+/* Experiment: each cycle, try to hold sub-unity gain until inflight <= BDP. */
+static bool bbr_drain_to_target = true;		/* default: enabled */
+
+/* Experiment: Flags to control BBR with ECN behavior.
+ */
+static bool bbr_precise_ece_ack = true;		/* default: enabled */
+
+/* The max rwin scaling shift factor is 14 (RFC 1323), so the max sane rwin is
+ * (2^(16+14) B)/(1024 B/packet) = 1M packets.
+ */
+static u32 bbr_cwnd_warn_val	= 1U << 20;
+
+static u16 bbr_debug_port_mask;
+
+/* BBR module parameters. These are module parameters only in Google prod.
+ * Upstream these are intentionally not module parameters.
+ */
+static int bbr_pacing_gain_size = CYCLE_LEN;
+
+/* Gain factor for adding extra_acked to target cwnd: */
+static int bbr_extra_acked_gain = 256;
+
+/* Window length of extra_acked window. Max allowed val is 31. */
+static u32 bbr_extra_acked_win_rtts = 5;
+
+/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */
+static u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20;
+
+/* Time period for clamping cwnd increment due to ack aggregation */
+static u32 bbr_extra_acked_max_us = 100 * 1000;
+
+/* Use extra acked in startup ?
+ * 0: disabled
+ * 1: use latest extra_acked value from 1-2 rtt in startup
+ */
+static int bbr_extra_acked_in_startup = 1;		/* default: enabled */
+
+/* Experiment: don't grow cwnd beyond twice of what we just probed. */
+static bool bbr_usage_based_cwnd;		/* default: disabled */
+
+/* For lab testing, researchers can enable BBRv2 ECN support with this flag,
+ * when they know that any ECN marks that the connections experience will be
+ * DCTCP/L4S-style ECN marks, rather than RFC3168 ECN marks.
+ * TODO(ncardwell): Production use of the BBRv2 ECN functionality depends on
+ * negotiation or configuration that is outside the scope of the BBRv2
+ * alpha release.
+ */
+static bool bbr_ecn_enable = false;
+
+module_param_named(min_tso_rate,      bbr_min_tso_rate,      int,    0644);
+module_param_named(tso_rtt_shift,     bbr_tso_rtt_shift,     int,    0644);
+module_param_named(high_gain,         bbr_high_gain,         int,    0644);
+module_param_named(drain_gain,        bbr_drain_gain,        int,    0644);
+module_param_named(startup_cwnd_gain, bbr_startup_cwnd_gain, int,    0644);
+module_param_named(cwnd_gain,         bbr_cwnd_gain,         int,    0644);
+module_param_array_named(pacing_gain, bbr_pacing_gain,       int,
+			 &bbr_pacing_gain_size, 0644);
+module_param_named(cwnd_min_target,   bbr_cwnd_min_target,   uint,   0644);
+module_param_named(probe_rtt_cwnd_gain,
+		   bbr_probe_rtt_cwnd_gain,		     uint,   0664);
+module_param_named(cwnd_warn_val,     bbr_cwnd_warn_val,     uint,   0664);
+module_param_named(debug_port_mask,   bbr_debug_port_mask,   ushort, 0644);
+module_param_named(flags,             bbr_flags,             uint,   0644);
+module_param_named(debug_ftrace,      bbr_debug_ftrace, bool,   0644);
+module_param_named(debug_with_printk, bbr_debug_with_printk, bool,   0644);
+module_param_named(min_rtt_win_sec,   bbr_min_rtt_win_sec,   uint,   0644);
+module_param_named(probe_rtt_mode_ms, bbr_probe_rtt_mode_ms, uint,   0644);
+module_param_named(probe_rtt_win_ms,  bbr_probe_rtt_win_ms,  uint,   0644);
+module_param_named(full_bw_thresh,    bbr_full_bw_thresh,    uint,   0644);
+module_param_named(full_bw_cnt,       bbr_full_bw_cnt,       uint,   0644);
+module_param_named(cwnd_tso_bduget,   bbr_cwnd_tso_budget,   uint,   0664);
+module_param_named(extra_acked_gain,  bbr_extra_acked_gain,  int,    0664);
+module_param_named(extra_acked_win_rtts,
+		   bbr_extra_acked_win_rtts, uint,   0664);
+module_param_named(extra_acked_max_us,
+		   bbr_extra_acked_max_us, uint,   0664);
+module_param_named(ack_epoch_acked_reset_thresh,
+		   bbr_ack_epoch_acked_reset_thresh, uint,   0664);
+module_param_named(drain_to_target,   bbr_drain_to_target,   bool,   0664);
+module_param_named(precise_ece_ack,   bbr_precise_ece_ack,   bool,   0664);
+module_param_named(extra_acked_in_startup,
+		   bbr_extra_acked_in_startup, int, 0664);
+module_param_named(usage_based_cwnd, bbr_usage_based_cwnd, bool,   0664);
+module_param_named(ecn_enable,       bbr_ecn_enable,         bool,   0664);
+
+static void bbr2_exit_probe_rtt(struct sock *sk);
+static void bbr2_reset_congestion_signals(struct sock *sk);
+
+static void bbr_check_probe_rtt_done(struct sock *sk);
+
+/* Do we estimate that STARTUP filled the pipe? */
+static bool bbr_full_bw_reached(const struct sock *sk)
+{
+	const struct bbr *bbr = inet_csk_ca(sk);
+
+	return bbr->full_bw_reached;
+}
+
+/* Return the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */
+static u32 bbr_max_bw(const struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	return max(bbr->bw_hi[0], bbr->bw_hi[1]);
+}
+
+/* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */
+static u32 bbr_bw(const struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	return min(bbr_max_bw(sk), bbr->bw_lo);
+}
+
+/* Return maximum extra acked in past k-2k round trips,
+ * where k = bbr_extra_acked_win_rtts.
+ */
+static u16 bbr_extra_acked(const struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	return max(bbr->extra_acked[0], bbr->extra_acked[1]);
+}
+
+/* Return rate in bytes per second, optionally with a gain.
+ * The order here is chosen carefully to avoid overflow of u64. This should
+ * work for input rates of up to 2.9Tbit/sec and gain of 2.89x.
+ */
+static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain,
+				  int margin)
+{
+	unsigned int mss = tcp_sk(sk)->mss_cache;
+
+	rate *= mss;
+	rate *= gain;
+	rate >>= BBR_SCALE;
+	rate *= USEC_PER_SEC / 100 * (100 - margin);
+	rate >>= BW_SCALE;
+	rate = max(rate, 1ULL);
+	return rate;
+}
+
+static u64 bbr_bw_bytes_per_sec(struct sock *sk, u64 rate)
+{
+	return bbr_rate_bytes_per_sec(sk, rate, BBR_UNIT, 0);
+}
+
+static u64 bbr_rate_kbps(struct sock *sk, u64 rate)
+{
+	rate = bbr_bw_bytes_per_sec(sk, rate);
+	rate *= 8;
+	do_div(rate, 1000);
+	return rate;
+}
+
+static u32 bbr_tso_segs_goal(struct sock *sk);
+static void bbr_debug(struct sock *sk, u32 acked,
+		      const struct rate_sample *rs, struct bbr_context *ctx)
+{
+	static const char ca_states[] = {
+		[TCP_CA_Open]		= 'O',
+		[TCP_CA_Disorder]	= 'D',
+		[TCP_CA_CWR]		= 'C',
+		[TCP_CA_Recovery]	= 'R',
+		[TCP_CA_Loss]		= 'L',
+	};
+	static const char mode[] = {
+		'G',  /* Growing   - BBR_STARTUP */
+		'D',  /* Drain     - BBR_DRAIN */
+		'W',  /* Window    - BBR_PROBE_BW */
+		'M',  /* Min RTT   - BBR_PROBE_RTT */
+	};
+	static const char ack_phase[] = { /* bbr_ack_phase strings */
+		'I',	/* BBR_ACKS_INIT	   - 'Init' */
+		'R',	/* BBR_ACKS_REFILLING	   - 'Refilling' */
+		'B',	/* BBR_ACKS_PROBE_STARTING - 'Before' */
+		'F',	/* BBR_ACKS_PROBE_FEEDBACK - 'Feedback' */
+		'A',	/* BBR_ACKS_PROBE_STOPPING - 'After' */
+	};
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	const u32 una = tp->snd_una - bbr->debug.snd_isn;
+	const u32 fack = tcp_highest_sack_seq(tp);
+	const u16 dport = ntohs(inet_sk(sk)->inet_dport);
+	bool is_port_match = (bbr_debug_port_mask &&
+			      ((dport & bbr_debug_port_mask) == 0));
+	char debugmsg[320];
+
+	if (sk->sk_state == TCP_SYN_SENT)
+		return;  /* no bbr_init() yet if SYN retransmit -> CA_Loss */
+
+	if (!tp->snd_cwnd || tp->snd_cwnd > bbr_cwnd_warn_val) {
+		char addr[INET6_ADDRSTRLEN + 10] = { 0 };
+
+		if (sk->sk_family == AF_INET)
+			snprintf(addr, sizeof(addr), "%pI4:%u",
+				 &inet_sk(sk)->inet_daddr, dport);
+		else if (sk->sk_family == AF_INET6)
+			snprintf(addr, sizeof(addr), "%pI6:%u",
+				 &sk->sk_v6_daddr, dport);
+
+		WARN_ONCE(1,
+			"BBR %s cwnd alert: %u "
+			"snd_una: %u ca: %d pacing_gain: %u cwnd_gain: %u "
+			"bw: %u rtt: %u min_rtt: %u "
+			"acked: %u tso_segs: %u "
+			"bw: %d %ld %d pif: %u\n",
+			addr, tp->snd_cwnd,
+			una, inet_csk(sk)->icsk_ca_state,
+			bbr->pacing_gain, bbr->cwnd_gain,
+			bbr_max_bw(sk), (tp->srtt_us >> 3), bbr->min_rtt_us,
+			acked, bbr_tso_segs_goal(sk),
+			rs->delivered, rs->interval_us, rs->is_retrans,
+			tcp_packets_in_flight(tp));
+	}
+
+	if (likely(!bbr_debug_with_printk && !bbr_debug_ftrace))
+		return;
+
+	if (!sock_flag(sk, SOCK_DBG) && !is_port_match)
+		return;
+
+	if (!ctx->log && !tp->app_limited && !(bbr_flags & FLAG_DEBUG_VERBOSE))
+		return;
+
+	if (ipv4_is_loopback(inet_sk(sk)->inet_daddr) &&
+	    !(bbr_flags & FLAG_DEBUG_LOOPBACK))
+		return;
+
+	snprintf(debugmsg, sizeof(debugmsg) - 1,
+		 "BBR %pI4:%-5u %5u,%03u:%-7u %c "
+		 "%c %2u br %2u cr %2d rtt %5ld d %2d i %5ld mrtt %d %cbw %llu "
+		 "bw %llu lb %llu ib %llu qb %llu "
+		 "a %u if %2u %c %c dl %u l %u al %u # %u t %u %c %c "
+		 "lr %d er %d ea %d bwl %lld il %d ih %d c %d "
+		 "v %d %c %u %c %s\n",
+		 &inet_sk(sk)->inet_daddr, dport,
+		 una / 1000, una % 1000, fack - tp->snd_una,
+		 ca_states[inet_csk(sk)->icsk_ca_state],
+		 bbr->debug.undo ? '@' : mode[bbr->mode],
+		 tp->snd_cwnd,
+		 bbr_extra_acked(sk),	/* br (legacy): extra_acked */
+		 rs->tx_in_flight,	/* cr (legacy): tx_inflight */
+		 rs->rtt_us,
+		 rs->delivered,
+		 rs->interval_us,
+		 bbr->min_rtt_us,
+		 rs->is_app_limited ? '_' : 'l',
+		 bbr_rate_kbps(sk, ctx->sample_bw), /* lbw: latest sample bw */
+		 bbr_rate_kbps(sk, bbr_max_bw(sk)), /* bw: max bw */
+		 0ULL,				    /* lb: [obsolete] */
+		 0ULL,				    /* ib: [obsolete] */
+		 div_u64((u64)sk->sk_pacing_rate * 8, 1000),
+		 acked,
+		 tcp_packets_in_flight(tp),
+		 rs->is_ack_delayed ? 'd' : '.',
+		 bbr->round_start ? '*' : '.',
+		 tp->delivered, tp->lost,
+		 tp->app_limited,
+		 0,			    	    /* #: [obsolete] */
+		 ctx->target_cwnd,
+		 tp->reord_seen ? 'r' : '.',  /* r: reordering seen? */
+		 ca_states[bbr->prev_ca_state],
+		 (rs->lost + rs->delivered) > 0 ?
+		 (1000 * rs->lost /
+		  (rs->lost + rs->delivered)) : 0,    /* lr: loss rate x1000 */
+		 (rs->delivered) > 0 ?
+		 (1000 * rs->delivered_ce /
+		  (rs->delivered)) : 0,		      /* er: ECN rate x1000 */
+		 1000 * bbr->ecn_alpha >> BBR_SCALE,  /* ea: ECN alpha x1000 */
+		 bbr->bw_lo == ~0U ?
+		   -1 : (s64)bbr_rate_kbps(sk, bbr->bw_lo), /* bwl */
+		 bbr->inflight_lo,	/* il */
+		 bbr->inflight_hi,	/* ih */
+		 bbr->bw_probe_up_cnt,	/* c */
+		 2,			/* v: version */
+		 bbr->debug.event,
+		 bbr->cycle_idx,
+		 ack_phase[bbr->ack_phase],
+		 bbr->bw_probe_samples ? "Y" : "N");
+	debugmsg[sizeof(debugmsg) - 1] = 0;
+
+	/* printk takes a higher precedence. */
+	if (bbr_debug_with_printk)
+		printk(KERN_DEBUG "%s", debugmsg);
+
+	if (unlikely(bbr->debug.undo))
+		bbr->debug.undo = 0;
+}
+
+/* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */
+static unsigned long bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)
+{
+	u64 rate = bw;
+
+	rate = bbr_rate_bytes_per_sec(sk, rate, gain,
+				      bbr_pacing_margin_percent);
+	rate = min_t(u64, rate, sk->sk_max_pacing_rate);
+	return rate;
+}
+
+/* Initialize pacing rate to: high_gain * init_cwnd / RTT. */
+static void bbr_init_pacing_rate_from_rtt(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u64 bw;
+	u32 rtt_us;
+
+	if (tp->srtt_us) {		/* any RTT sample yet? */
+		rtt_us = max(tp->srtt_us >> 3, 1U);
+		bbr->has_seen_rtt = 1;
+	} else {			 /* no RTT sample yet */
+		rtt_us = USEC_PER_MSEC;	 /* use nominal default RTT */
+	}
+	bw = (u64)tp->snd_cwnd * BW_UNIT;
+	do_div(bw, rtt_us);
+	sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr->params.high_gain);
+}
+
+/* Pace using current bw estimate and a gain factor. */
+static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	unsigned long rate = bbr_bw_to_pacing_rate(sk, bw, gain);
+
+	if (unlikely(!bbr->has_seen_rtt && tp->srtt_us))
+		bbr_init_pacing_rate_from_rtt(sk);
+	if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate)
+		sk->sk_pacing_rate = rate;
+}
+
+static u32 bbr_min_tso_segs(struct sock *sk)
+{
+	return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
+}
+
+/* Return the number of segments BBR would like in a TSO/GSO skb, given
+ * a particular max gso size as a constraint.
+ */
+static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now,
+				u32 gso_max_size)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 segs, r;
+	u64 bytes;
+
+	/* Budget a TSO/GSO burst size allowance based on bw (pacing_rate). */
+	bytes = sk->sk_pacing_rate >> sk->sk_pacing_shift;
+
+	/* Budget a TSO/GSO burst size allowance based on min_rtt. For every
+	 * K = 2^tso_rtt_shift microseconds of min_rtt, halve the burst.
+	 * The min_rtt-based burst allowance is: 64 KBytes / 2^(min_rtt/K)
+	 */
+	if (bbr->params.tso_rtt_shift) {
+		r = bbr->min_rtt_us >> bbr->params.tso_rtt_shift;
+		if (r < BITS_PER_TYPE(u32))   /* prevent undefined behavior */
+			bytes += GSO_MAX_SIZE >> r;
+	}
+
+	bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
+	segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk));
+	return segs;
+}
+
+/* Custom tcp_tso_autosize() for BBR, used at transmit time to cap skb size. */
+static u32  bbr_tso_segs(struct sock *sk, unsigned int mss_now)
+{
+	return bbr_tso_segs_generic(sk, mss_now, sk->sk_gso_max_size);
+}
+
+/* Like bbr_tso_segs(), using mss_cache, ignoring driver's sk_gso_max_size. */
+static u32 bbr_tso_segs_goal(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	return  bbr_tso_segs_generic(sk, tp->mss_cache, GSO_MAX_SIZE);
+}
+
+/* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
+static void bbr_save_cwnd(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT)
+		bbr->prior_cwnd = tp->snd_cwnd;  /* this cwnd is good enough */
+	else  /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */
+		bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd);
+}
+
+static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (event == CA_EVENT_TX_START && tp->app_limited) {
+		bbr->idle_restart = 1;
+		bbr->ack_epoch_mstamp = tp->tcp_mstamp;
+		bbr->ack_epoch_acked = 0;
+		/* Avoid pointless buffer overflows: pace at est. bw if we don't
+		 * need more speed (we're restarting from idle and app-limited).
+		 */
+		if (bbr->mode == BBR_PROBE_BW)
+			bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT);
+		else if (bbr->mode == BBR_PROBE_RTT)
+			bbr_check_probe_rtt_done(sk);
+	} else if ((event == CA_EVENT_ECN_IS_CE ||
+		    event == CA_EVENT_ECN_NO_CE) &&
+		    bbr_ecn_enable &&
+		    bbr->params.precise_ece_ack) {
+		u32 state = bbr->ce_state;
+		dctcp_ece_ack_update(sk, event, &bbr->prior_rcv_nxt, &state);
+		bbr->ce_state = state;
+		if (tp->fast_ack_mode == 2 && event == CA_EVENT_ECN_IS_CE)
+			tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
+	}
+}
+
+/* Calculate bdp based on min RTT and the estimated bottleneck bandwidth:
+ *
+ * bdp = ceil(bw * min_rtt * gain)
+ *
+ * The key factor, gain, controls the amount of queue. While a small gain
+ * builds a smaller queue, it becomes more vulnerable to noise in RTT
+ * measurements (e.g., delayed ACKs or other ACK compression effects). This
+ * noise may cause BBR to under-estimate the rate.
+ */
+static u32 bbr_bdp(struct sock *sk, u32 bw, int gain)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 bdp;
+	u64 w;
+
+	/* If we've never had a valid RTT sample, cap cwnd at the initial
+	 * default. This should only happen when the connection is not using TCP
+	 * timestamps and has retransmitted all of the SYN/SYNACK/data packets
+	 * ACKed so far. In this case, an RTO can cut cwnd to 1, in which
+	 * case we need to slow-start up toward something safe: initial cwnd.
+	 */
+	if (unlikely(bbr->min_rtt_us == ~0U))	 /* no valid RTT samples yet? */
+		return bbr->init_cwnd;  /* be safe: cap at initial cwnd */
+
+	w = (u64)bw * bbr->min_rtt_us;
+
+	/* Apply a gain to the given value, remove the BW_SCALE shift, and
+	 * round the value up to avoid a negative feedback loop.
+	 */
+	bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT;
+
+	return bdp;
+}
+
+/* To achieve full performance in high-speed paths, we budget enough cwnd to
+ * fit full-sized skbs in-flight on both end hosts to fully utilize the path:
+ *   - one skb in sending host Qdisc,
+ *   - one skb in sending host TSO/GSO engine
+ *   - one skb being received by receiver host LRO/GRO/delayed-ACK engine
+ * Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because
+ * in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets,
+ * which allows 2 outstanding 2-packet sequences, to try to keep pipe
+ * full even with ACK-every-other-packet delayed ACKs.
+ */
+static u32 bbr_quantization_budget(struct sock *sk, u32 cwnd)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 tso_segs_goal;
+
+	tso_segs_goal = 3 * bbr_tso_segs_goal(sk);
+
+	/* Allow enough full-sized skbs in flight to utilize end systems. */
+	if (bbr->params.cwnd_tso_budget == 1) {
+		cwnd = max_t(u32, cwnd, tso_segs_goal);
+		cwnd = max_t(u32, cwnd, bbr->params.cwnd_min_target);
+	} else {
+		cwnd += tso_segs_goal;
+		cwnd = (cwnd + 1) & ~1U;
+	}
+	/* Ensure gain cycling gets inflight above BDP even for small BDPs. */
+	if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == BBR_BW_PROBE_UP)
+		cwnd += 2;
+
+	return cwnd;
+}
+
+/* Find inflight based on min RTT and the estimated bottleneck bandwidth. */
+static u32 bbr_inflight(struct sock *sk, u32 bw, int gain)
+{
+	u32 inflight;
+
+	inflight = bbr_bdp(sk, bw, gain);
+	inflight = bbr_quantization_budget(sk, inflight);
+
+	return inflight;
+}
+
+/* With pacing at lower layers, there's often less data "in the network" than
+ * "in flight". With TSQ and departure time pacing at lower layers (e.g. fq),
+ * we often have several skbs queued in the pacing layer with a pre-scheduled
+ * earliest departure time (EDT). BBR adapts its pacing rate based on the
+ * inflight level that it estimates has already been "baked in" by previous
+ * departure time decisions. We calculate a rough estimate of the number of our
+ * packets that might be in the network at the earliest departure time for the
+ * next skb scheduled:
+ *   in_network_at_edt = inflight_at_edt - (EDT - now) * bw
+ * If we're increasing inflight, then we want to know if the transmit of the
+ * EDT skb will push inflight above the target, so inflight_at_edt includes
+ * bbr_tso_segs_goal() from the skb departing at EDT. If decreasing inflight,
+ * then estimate if inflight will sink too low just before the EDT transmit.
+ */
+static u32 bbr_packets_in_net_at_edt(struct sock *sk, u32 inflight_now)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u64 now_ns, edt_ns, interval_us;
+	u32 interval_delivered, inflight_at_edt;
+
+	now_ns = tp->tcp_clock_cache;
+	edt_ns = max(tp->tcp_wstamp_ns, now_ns);
+	interval_us = div_u64(edt_ns - now_ns, NSEC_PER_USEC);
+	interval_delivered = (u64)bbr_bw(sk) * interval_us >> BW_SCALE;
+	inflight_at_edt = inflight_now;
+	if (bbr->pacing_gain > BBR_UNIT)              /* increasing inflight */
+		inflight_at_edt += bbr_tso_segs_goal(sk);  /* include EDT skb */
+	if (interval_delivered >= inflight_at_edt)
+		return 0;
+	return inflight_at_edt - interval_delivered;
+}
+
+/* Find the cwnd increment based on estimate of ack aggregation */
+static u32 bbr_ack_aggregation_cwnd(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 max_aggr_cwnd, aggr_cwnd = 0;
+
+	if (bbr->params.extra_acked_gain &&
+	    (bbr_full_bw_reached(sk) || bbr->params.extra_acked_in_startup)) {
+		max_aggr_cwnd = ((u64)bbr_bw(sk) * bbr_extra_acked_max_us)
+				/ BW_UNIT;
+		aggr_cwnd = (bbr->params.extra_acked_gain * bbr_extra_acked(sk))
+			     >> BBR_SCALE;
+		aggr_cwnd = min(aggr_cwnd, max_aggr_cwnd);
+	}
+
+	return aggr_cwnd;
+}
+
+/* Returns the cwnd for PROBE_RTT mode. */
+static u32 bbr_probe_rtt_cwnd(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr->params.probe_rtt_cwnd_gain == 0)
+		return bbr->params.cwnd_min_target;
+	return max_t(u32, bbr->params.cwnd_min_target,
+		     bbr_bdp(sk, bbr_bw(sk), bbr->params.probe_rtt_cwnd_gain));
+}
+
+/* Slow-start up toward target cwnd (if bw estimate is growing, or packet loss
+ * has drawn us down below target), or snap down to target if we're above it.
+ */
+static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs,
+			 u32 acked, u32 bw, int gain, u32 cwnd,
+			 struct bbr_context *ctx)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 target_cwnd = 0, prev_cwnd = tp->snd_cwnd, max_probe;
+
+	if (!acked)
+		goto done;  /* no packet fully ACKed; just apply caps */
+
+	target_cwnd = bbr_bdp(sk, bw, gain);
+
+	/* Increment the cwnd to account for excess ACKed data that seems
+	 * due to aggregation (of data and/or ACKs) visible in the ACK stream.
+	 */
+	target_cwnd += bbr_ack_aggregation_cwnd(sk);
+	target_cwnd = bbr_quantization_budget(sk, target_cwnd);
+
+	/* If we're below target cwnd, slow start cwnd toward target cwnd. */
+	bbr->debug.target_cwnd = target_cwnd;
+
+	/* Update cwnd and enable fast path if cwnd reaches target_cwnd. */
+	bbr->try_fast_path = 0;
+	if (bbr_full_bw_reached(sk)) { /* only cut cwnd if we filled the pipe */
+		cwnd += acked;
+		if (cwnd >= target_cwnd) {
+			cwnd = target_cwnd;
+			bbr->try_fast_path = 1;
+		}
+	} else if (cwnd < target_cwnd || cwnd  < 2 * bbr->init_cwnd) {
+		cwnd += acked;
+	} else {
+		bbr->try_fast_path = 1;
+	}
+
+	/* When growing cwnd, don't grow beyond twice what we just probed. */
+	if (bbr->params.usage_based_cwnd) {
+		max_probe = max(2 * tp->max_packets_out, tp->snd_cwnd);
+		cwnd = min(cwnd, max_probe);
+	}
+
+	cwnd = max_t(u32, cwnd, bbr->params.cwnd_min_target);
+done:
+	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);	/* apply global cap */
+	if (bbr->mode == BBR_PROBE_RTT)  /* drain queue, refresh min_rtt */
+		tp->snd_cwnd = min_t(u32, tp->snd_cwnd, bbr_probe_rtt_cwnd(sk));
+
+	ctx->target_cwnd = target_cwnd;
+	ctx->log = (tp->snd_cwnd != prev_cwnd);
+}
+
+/* See if we have reached next round trip */
+static void bbr_update_round_start(struct sock *sk,
+		const struct rate_sample *rs, struct bbr_context *ctx)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->round_start = 0;
+
+	/* See if we've reached the next RTT */
+	if (rs->interval_us > 0 &&
+	    !before(rs->prior_delivered, bbr->next_rtt_delivered)) {
+		bbr->next_rtt_delivered = tp->delivered;
+		bbr->round_start = 1;
+	}
+}
+
+/* Calculate the bandwidth based on how fast packets are delivered */
+static void bbr_calculate_bw_sample(struct sock *sk,
+			const struct rate_sample *rs, struct bbr_context *ctx)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u64 bw = 0;
+
+	/* Divide delivered by the interval to find a (lower bound) bottleneck
+	 * bandwidth sample. Delivered is in packets and interval_us in uS and
+	 * ratio will be <<1 for most connections. So delivered is first scaled.
+	 * Round up to allow growth at low rates, even with integer division.
+	 */
+	if (rs->interval_us > 0) {
+		if (WARN_ONCE(rs->delivered < 0,
+			      "negative delivered: %d interval_us: %ld\n",
+			      rs->delivered, rs->interval_us))
+			return;
+
+		bw = DIV_ROUND_UP_ULL((u64)rs->delivered * BW_UNIT, rs->interval_us);
+	}
+
+	ctx->sample_bw = bw;
+	bbr->debug.rs_bw = bw;
+}
+
+/* Estimates the windowed max degree of ack aggregation.
+ * This is used to provision extra in-flight data to keep sending during
+ * inter-ACK silences.
+ *
+ * Degree of ack aggregation is estimated as extra data acked beyond expected.
+ *
+ * max_extra_acked = "maximum recent excess data ACKed beyond max_bw * interval"
+ * cwnd += max_extra_acked
+ *
+ * Max extra_acked is clamped by cwnd and bw * bbr_extra_acked_max_us (100 ms).
+ * Max filter is an approximate sliding window of 5-10 (packet timed) round
+ * trips for non-startup phase, and 1-2 round trips for startup.
+ */
+static void bbr_update_ack_aggregation(struct sock *sk,
+				       const struct rate_sample *rs)
+{
+	u32 epoch_us, expected_acked, extra_acked;
+	struct bbr *bbr = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 extra_acked_win_rtts_thresh = bbr->params.extra_acked_win_rtts;
+
+	if (!bbr->params.extra_acked_gain || rs->acked_sacked <= 0 ||
+	    rs->delivered < 0 || rs->interval_us <= 0)
+		return;
+
+	if (bbr->round_start) {
+		bbr->extra_acked_win_rtts = min(0x1F,
+						bbr->extra_acked_win_rtts + 1);
+		if (bbr->params.extra_acked_in_startup &&
+		    !bbr_full_bw_reached(sk))
+			extra_acked_win_rtts_thresh = 1;
+		if (bbr->extra_acked_win_rtts >=
+		    extra_acked_win_rtts_thresh) {
+			bbr->extra_acked_win_rtts = 0;
+			bbr->extra_acked_win_idx = bbr->extra_acked_win_idx ?
+						   0 : 1;
+			bbr->extra_acked[bbr->extra_acked_win_idx] = 0;
+		}
+	}
+
+	/* Compute how many packets we expected to be delivered over epoch. */
+	epoch_us = tcp_stamp_us_delta(tp->delivered_mstamp,
+				      bbr->ack_epoch_mstamp);
+	expected_acked = ((u64)bbr_bw(sk) * epoch_us) / BW_UNIT;
+
+	/* Reset the aggregation epoch if ACK rate is below expected rate or
+	 * significantly large no. of ack received since epoch (potentially
+	 * quite old epoch).
+	 */
+	if (bbr->ack_epoch_acked <= expected_acked ||
+	    (bbr->ack_epoch_acked + rs->acked_sacked >=
+	     bbr_ack_epoch_acked_reset_thresh)) {
+		bbr->ack_epoch_acked = 0;
+		bbr->ack_epoch_mstamp = tp->delivered_mstamp;
+		expected_acked = 0;
+	}
+
+	/* Compute excess data delivered, beyond what was expected. */
+	bbr->ack_epoch_acked = min_t(u32, 0xFFFFF,
+				   bbr->ack_epoch_acked + rs->acked_sacked);
+	extra_acked = bbr->ack_epoch_acked - expected_acked;
+	extra_acked = min(extra_acked, tp->snd_cwnd);
+	if (extra_acked > bbr->extra_acked[bbr->extra_acked_win_idx])
+		bbr->extra_acked[bbr->extra_acked_win_idx] = extra_acked;
+}
+
+/* Estimate when the pipe is full, using the change in delivery rate: BBR
+ * estimates that STARTUP filled the pipe if the estimated bw hasn't changed by
+ * at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) non-app-limited
+ * rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill the
+ * higher rwin, 3: we get higher delivery rate samples. Or transient
+ * cross-traffic or radio noise can go away. CUBIC Hystart shares a similar
+ * design goal, but uses delay and inter-ACK spacing instead of bandwidth.
+ */
+static void bbr_check_full_bw_reached(struct sock *sk,
+				      const struct rate_sample *rs)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 bw_thresh;
+
+	if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited)
+		return;
+
+	bw_thresh = (u64)bbr->full_bw * bbr->params.full_bw_thresh >> BBR_SCALE;
+	if (bbr_max_bw(sk) >= bw_thresh) {
+		bbr->full_bw = bbr_max_bw(sk);
+		bbr->full_bw_cnt = 0;
+		return;
+	}
+	++bbr->full_bw_cnt;
+	bbr->full_bw_reached = bbr->full_bw_cnt >= bbr->params.full_bw_cnt;
+}
+
+/* If pipe is probably full, drain the queue and then enter steady-state. */
+static bool bbr_check_drain(struct sock *sk, const struct rate_sample *rs,
+			    struct bbr_context *ctx)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) {
+		bbr->mode = BBR_DRAIN;	/* drain queue we created */
+		tcp_sk(sk)->snd_ssthresh =
+				bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT);
+		bbr2_reset_congestion_signals(sk);
+	}	/* fall through to check if in-flight is already small: */
+	if (bbr->mode == BBR_DRAIN &&
+	    bbr_packets_in_net_at_edt(sk, tcp_packets_in_flight(tcp_sk(sk))) <=
+	    bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT))
+		return true;  /* exiting DRAIN now */
+	return false;
+}
+
+static void bbr_check_probe_rtt_done(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (!(bbr->probe_rtt_done_stamp &&
+	      after(tcp_jiffies32, bbr->probe_rtt_done_stamp)))
+		return;
+
+	bbr->probe_rtt_min_stamp = tcp_jiffies32; /* schedule next PROBE_RTT */
+	tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd);
+	bbr2_exit_probe_rtt(sk);
+}
+
+/* The goal of PROBE_RTT mode is to have BBR flows cooperatively and
+ * periodically drain the bottleneck queue, to converge to measure the true
+ * min_rtt (unloaded propagation delay). This allows the flows to keep queues
+ * small (reducing queuing delay and packet loss) and achieve fairness among
+ * BBR flows.
+ *
+ * The min_rtt filter window is 10 seconds. When the min_rtt estimate expires,
+ * we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 packets.
+ * After at least bbr_probe_rtt_mode_ms=200ms and at least one packet-timed
+ * round trip elapsed with that flight size <= 4, we leave PROBE_RTT mode and
+ * re-enter the previous mode. BBR uses 200ms to approximately bound the
+ * performance penalty of PROBE_RTT's cwnd capping to roughly 2% (200ms/10s).
+ *
+ * Note that flows need only pay 2% if they are busy sending over the last 10
+ * seconds. Interactive applications (e.g., Web, RPCs, video chunks) often have
+ * natural silences or low-rate periods within 10 seconds where the rate is low
+ * enough for long enough to drain its queue in the bottleneck. We pick up
+ * these min RTT measurements opportunistically with our min_rtt filter. :-)
+ */
+static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	bool probe_rtt_expired, min_rtt_expired;
+	u32 expire;
+
+	/* Track min RTT in probe_rtt_win_ms to time next PROBE_RTT state. */
+	expire = bbr->probe_rtt_min_stamp +
+		 msecs_to_jiffies(bbr->params.probe_rtt_win_ms);
+	probe_rtt_expired = after(tcp_jiffies32, expire);
+	if (rs->rtt_us >= 0 &&
+	    (rs->rtt_us <= bbr->probe_rtt_min_us ||
+	     (probe_rtt_expired && !rs->is_ack_delayed))) {
+		bbr->probe_rtt_min_us = rs->rtt_us;
+		bbr->probe_rtt_min_stamp = tcp_jiffies32;
+	}
+	/* Track min RTT seen in the min_rtt_win_sec filter window: */
+	expire = bbr->min_rtt_stamp + bbr->params.min_rtt_win_sec * HZ;
+	min_rtt_expired = after(tcp_jiffies32, expire);
+	if (bbr->probe_rtt_min_us <= bbr->min_rtt_us ||
+	    min_rtt_expired) {
+		bbr->min_rtt_us = bbr->probe_rtt_min_us;
+		bbr->min_rtt_stamp = bbr->probe_rtt_min_stamp;
+	}
+
+	if (bbr->params.probe_rtt_mode_ms > 0 && probe_rtt_expired &&
+	    !bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) {
+		bbr->mode = BBR_PROBE_RTT;  /* dip, drain queue */
+		bbr_save_cwnd(sk);  /* note cwnd so we can restore it */
+		bbr->probe_rtt_done_stamp = 0;
+		bbr->ack_phase = BBR_ACKS_PROBE_STOPPING;
+		bbr->next_rtt_delivered = tp->delivered;
+	}
+
+	if (bbr->mode == BBR_PROBE_RTT) {
+		/* Ignore low rate samples during this mode. */
+		tp->app_limited =
+			(tp->delivered + tcp_packets_in_flight(tp)) ? : 1;
+		/* Maintain min packets in flight for max(200 ms, 1 round). */
+		if (!bbr->probe_rtt_done_stamp &&
+		    tcp_packets_in_flight(tp) <= bbr_probe_rtt_cwnd(sk)) {
+			bbr->probe_rtt_done_stamp = tcp_jiffies32 +
+				msecs_to_jiffies(bbr->params.probe_rtt_mode_ms);
+			bbr->probe_rtt_round_done = 0;
+			bbr->next_rtt_delivered = tp->delivered;
+		} else if (bbr->probe_rtt_done_stamp) {
+			if (bbr->round_start)
+				bbr->probe_rtt_round_done = 1;
+			if (bbr->probe_rtt_round_done)
+				bbr_check_probe_rtt_done(sk);
+		}
+	}
+	/* Restart after idle ends only once we process a new S/ACK for data */
+	if (rs->delivered > 0)
+		bbr->idle_restart = 0;
+}
+
+static void bbr_update_gains(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	switch (bbr->mode) {
+	case BBR_STARTUP:
+		bbr->pacing_gain = bbr->params.high_gain;
+		bbr->cwnd_gain	 = bbr->params.startup_cwnd_gain;
+		break;
+	case BBR_DRAIN:
+		bbr->pacing_gain = bbr->params.drain_gain;  /* slow, to drain */
+		bbr->cwnd_gain = bbr->params.startup_cwnd_gain;  /* keep cwnd */
+		break;
+	case BBR_PROBE_BW:
+		bbr->pacing_gain = bbr->params.pacing_gain[bbr->cycle_idx];
+		bbr->cwnd_gain = bbr->params.cwnd_gain;
+		break;
+	case BBR_PROBE_RTT:
+		bbr->pacing_gain = BBR_UNIT;
+		bbr->cwnd_gain = BBR_UNIT;
+		break;
+	default:
+		WARN_ONCE(1, "BBR bad mode: %u\n", bbr->mode);
+		break;
+	}
+}
+
+static void bbr_init(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	int i;
+
+	WARN_ON_ONCE(tp->snd_cwnd >= bbr_cwnd_warn_val);
+
+	bbr->initialized = 1;
+	bbr->params.high_gain = min(0x7FF, bbr_high_gain);
+	bbr->params.drain_gain = min(0x3FF, bbr_drain_gain);
+	bbr->params.startup_cwnd_gain = min(0x7FF, bbr_startup_cwnd_gain);
+	bbr->params.cwnd_gain = min(0x7FF, bbr_cwnd_gain);
+	bbr->params.cwnd_tso_budget = min(0x1U, bbr_cwnd_tso_budget);
+	bbr->params.cwnd_min_target = min(0xFU, bbr_cwnd_min_target);
+	bbr->params.min_rtt_win_sec = min(0x1FU, bbr_min_rtt_win_sec);
+	bbr->params.probe_rtt_mode_ms = min(0x1FFU, bbr_probe_rtt_mode_ms);
+	bbr->params.full_bw_cnt = min(0x7U, bbr_full_bw_cnt);
+	bbr->params.full_bw_thresh = min(0x3FFU, bbr_full_bw_thresh);
+	bbr->params.extra_acked_gain = min(0x7FF, bbr_extra_acked_gain);
+	bbr->params.extra_acked_win_rtts = min(0x1FU, bbr_extra_acked_win_rtts);
+	bbr->params.drain_to_target = bbr_drain_to_target ? 1 : 0;
+	bbr->params.precise_ece_ack = bbr_precise_ece_ack ? 1 : 0;
+	bbr->params.extra_acked_in_startup = bbr_extra_acked_in_startup ? 1 : 0;
+	bbr->params.probe_rtt_cwnd_gain = min(0xFFU, bbr_probe_rtt_cwnd_gain);
+	bbr->params.probe_rtt_win_ms =
+		min(0x3FFFU,
+		    min_t(u32, bbr_probe_rtt_win_ms,
+			  bbr->params.min_rtt_win_sec * MSEC_PER_SEC));
+	for (i = 0; i < CYCLE_LEN; i++)
+		bbr->params.pacing_gain[i] = min(0x3FF, bbr_pacing_gain[i]);
+	bbr->params.usage_based_cwnd = bbr_usage_based_cwnd ? 1 : 0;
+	bbr->params.tso_rtt_shift =  min(0xFU, bbr_tso_rtt_shift);
+
+	bbr->debug.snd_isn = tp->snd_una;
+	bbr->debug.target_cwnd = 0;
+	bbr->debug.undo = 0;
+
+	bbr->init_cwnd = min(0x7FU, tp->snd_cwnd);
+	bbr->prior_cwnd = tp->prior_cwnd;
+	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
+	bbr->next_rtt_delivered = 0;
+	bbr->prev_ca_state = TCP_CA_Open;
+	bbr->packet_conservation = 0;
+
+	bbr->probe_rtt_done_stamp = 0;
+	bbr->probe_rtt_round_done = 0;
+	bbr->probe_rtt_min_us = tcp_min_rtt(tp);
+	bbr->probe_rtt_min_stamp = tcp_jiffies32;
+	bbr->min_rtt_us = tcp_min_rtt(tp);
+	bbr->min_rtt_stamp = tcp_jiffies32;
+
+	bbr->has_seen_rtt = 0;
+	bbr_init_pacing_rate_from_rtt(sk);
+
+	bbr->round_start = 0;
+	bbr->idle_restart = 0;
+	bbr->full_bw_reached = 0;
+	bbr->full_bw = 0;
+	bbr->full_bw_cnt = 0;
+	bbr->cycle_mstamp = 0;
+	bbr->cycle_idx = 0;
+	bbr->mode = BBR_STARTUP;
+	bbr->debug.rs_bw = 0;
+
+	bbr->ack_epoch_mstamp = tp->tcp_mstamp;
+	bbr->ack_epoch_acked = 0;
+	bbr->extra_acked_win_rtts = 0;
+	bbr->extra_acked_win_idx = 0;
+	bbr->extra_acked[0] = 0;
+	bbr->extra_acked[1] = 0;
+
+	bbr->ce_state = 0;
+	bbr->prior_rcv_nxt = tp->rcv_nxt;
+	bbr->try_fast_path = 0;
+
+	cmpxchg(&sk->sk_pacing_status, SK_PACING_NONE, SK_PACING_NEEDED);
+}
+
+static u32 bbr_sndbuf_expand(struct sock *sk)
+{
+	/* Provision 3 * cwnd since BBR may slow-start even during recovery. */
+	return 3;
+}
+
+/* __________________________________________________________________________
+ *
+ * Functions new to BBR v2 ("bbr") congestion control are below here.
+ * __________________________________________________________________________
+ */
+
+/* Incorporate a new bw sample into the current window of our max filter. */
+static void bbr2_take_bw_hi_sample(struct sock *sk, u32 bw)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->bw_hi[1] = max(bw, bbr->bw_hi[1]);
+}
+
+/* Keep max of last 1-2 cycles. Each PROBE_BW cycle, flip filter window. */
+static void bbr2_advance_bw_hi_filter(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (!bbr->bw_hi[1])
+		return;  /* no samples in this window; remember old window */
+	bbr->bw_hi[0] = bbr->bw_hi[1];
+	bbr->bw_hi[1] = 0;
+}
+
+/* How much do we want in flight? Our BDP, unless congestion cut cwnd. */
+static u32 bbr2_target_inflight(struct sock *sk)
+{
+	u32 bdp = bbr_inflight(sk, bbr_bw(sk), BBR_UNIT);
+
+	return min(bdp, tcp_sk(sk)->snd_cwnd);
+}
+
+static bool bbr2_is_probing_bandwidth(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	return (bbr->mode == BBR_STARTUP) ||
+		(bbr->mode == BBR_PROBE_BW &&
+		 (bbr->cycle_idx == BBR_BW_PROBE_REFILL ||
+		  bbr->cycle_idx == BBR_BW_PROBE_UP));
+}
+
+/* Has the given amount of time elapsed since we marked the phase start? */
+static bool bbr2_has_elapsed_in_phase(const struct sock *sk, u32 interval_us)
+{
+	const struct tcp_sock *tp = tcp_sk(sk);
+	const struct bbr *bbr = inet_csk_ca(sk);
+
+	return tcp_stamp_us_delta(tp->tcp_mstamp,
+				  bbr->cycle_mstamp + interval_us) > 0;
+}
+
+static void bbr2_handle_queue_too_high_in_startup(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->full_bw_reached = 1;
+	bbr->inflight_hi = bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT);
+}
+
+/* Exit STARTUP upon N consecutive rounds with ECN mark rate > ecn_thresh. */
+static void bbr2_check_ecn_too_high_in_startup(struct sock *sk, u32 ce_ratio)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr_full_bw_reached(sk) || !bbr->ecn_eligible ||
+	    !bbr->params.full_ecn_cnt || !bbr->params.ecn_thresh)
+		return;
+
+	if (ce_ratio >= bbr->params.ecn_thresh)
+		bbr->startup_ecn_rounds++;
+	else
+		bbr->startup_ecn_rounds = 0;
+
+	if (bbr->startup_ecn_rounds >= bbr->params.full_ecn_cnt) {
+		bbr->debug.event = 'E';  /* ECN caused STARTUP exit */
+		bbr2_handle_queue_too_high_in_startup(sk);
+		return;
+	}
+}
+
+static void bbr2_update_ecn_alpha(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	s32 delivered, delivered_ce;
+	u64 alpha, ce_ratio;
+	u32 gain;
+
+	if (bbr->params.ecn_factor == 0)
+		return;
+
+	delivered = tp->delivered - bbr->alpha_last_delivered;
+	delivered_ce = tp->delivered_ce - bbr->alpha_last_delivered_ce;
+
+	if (delivered == 0 ||		/* avoid divide by zero */
+	    WARN_ON_ONCE(delivered < 0 || delivered_ce < 0))  /* backwards? */
+		return;
+
+	/* See if we should use ECN sender logic for this connection. */
+	if (!bbr->ecn_eligible && bbr_ecn_enable &&
+	    (bbr->min_rtt_us <= bbr->params.ecn_max_rtt_us ||
+	     !bbr->params.ecn_max_rtt_us))
+		bbr->ecn_eligible = 1;
+
+	ce_ratio = (u64)delivered_ce << BBR_SCALE;
+	do_div(ce_ratio, delivered);
+	gain = bbr->params.ecn_alpha_gain;
+	alpha = ((BBR_UNIT - gain) * bbr->ecn_alpha) >> BBR_SCALE;
+	alpha += (gain * ce_ratio) >> BBR_SCALE;
+	bbr->ecn_alpha = min_t(u32, alpha, BBR_UNIT);
+
+	bbr->alpha_last_delivered = tp->delivered;
+	bbr->alpha_last_delivered_ce = tp->delivered_ce;
+
+	bbr2_check_ecn_too_high_in_startup(sk, ce_ratio);
+}
+
+/* Each round trip of BBR_BW_PROBE_UP, double volume of probing data. */
+static void bbr2_raise_inflight_hi_slope(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 growth_this_round, cnt;
+
+	/* Calculate "slope": packets S/Acked per inflight_hi increment. */
+	growth_this_round = 1 << bbr->bw_probe_up_rounds;
+	bbr->bw_probe_up_rounds = min(bbr->bw_probe_up_rounds + 1, 30);
+	cnt = tp->snd_cwnd / growth_this_round;
+	cnt = max(cnt, 1U);
+	bbr->bw_probe_up_cnt = cnt;
+	bbr->debug.event = 'G';  /* Grow inflight_hi slope */
+}
+
+/* In BBR_BW_PROBE_UP, not seeing high loss/ECN/queue, so raise inflight_hi. */
+static void bbr2_probe_inflight_hi_upward(struct sock *sk,
+					  const struct rate_sample *rs)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 delta;
+
+	if (!tp->is_cwnd_limited || tp->snd_cwnd < bbr->inflight_hi) {
+		bbr->bw_probe_up_acks = 0;  /* don't accmulate unused credits */
+		return;  /* not fully using inflight_hi, so don't grow it */
+	}
+
+	/* For each bw_probe_up_cnt packets ACKed, increase inflight_hi by 1. */
+	bbr->bw_probe_up_acks += rs->acked_sacked;
+	if (bbr->bw_probe_up_acks >=  bbr->bw_probe_up_cnt) {
+		delta = bbr->bw_probe_up_acks / bbr->bw_probe_up_cnt;
+		bbr->bw_probe_up_acks -= delta * bbr->bw_probe_up_cnt;
+		bbr->inflight_hi += delta;
+		bbr->debug.event = 'I';  /* Increment inflight_hi */
+	}
+
+	if (bbr->round_start)
+		bbr2_raise_inflight_hi_slope(sk);
+}
+
+/* Does loss/ECN rate for this sample say inflight is "too high"?
+ * This is used by both the bbr_check_loss_too_high_in_startup() function,
+ * which can be used in either v1 or v2, and the PROBE_UP phase of v2, which
+ * uses it to notice when loss/ECN rates suggest inflight is too high.
+ */
+static bool bbr2_is_inflight_too_high(const struct sock *sk,
+				     const struct rate_sample *rs)
+{
+	const struct bbr *bbr = inet_csk_ca(sk);
+	u32 loss_thresh, ecn_thresh;
+
+	if (rs->lost > 0 && rs->tx_in_flight) {
+		loss_thresh = (u64)rs->tx_in_flight * bbr->params.loss_thresh >>
+				BBR_SCALE;
+		if (rs->lost > loss_thresh)
+			return true;
+	}
+
+	if (rs->delivered_ce > 0 && rs->delivered > 0 &&
+	    bbr->ecn_eligible && bbr->params.ecn_thresh) {
+		ecn_thresh = (u64)rs->delivered * bbr->params.ecn_thresh >>
+				BBR_SCALE;
+		if (rs->delivered_ce >= ecn_thresh)
+			return true;
+	}
+
+	return false;
+}
+
+/* Calculate the tx_in_flight level that corresponded to excessive loss.
+ * We find "lost_prefix" segs of the skb where loss rate went too high,
+ * by solving for "lost_prefix" in the following equation:
+ *   lost                     /  inflight                     >= loss_thresh
+ *  (lost_prev + lost_prefix) / (inflight_prev + lost_prefix) >= loss_thresh
+ * Then we take that equation, convert it to fixed point, and
+ * round up to the nearest packet.
+ */
+static u32 bbr2_inflight_hi_from_lost_skb(const struct sock *sk,
+					  const struct rate_sample *rs,
+					  const struct sk_buff *skb)
+{
+	const struct bbr *bbr = inet_csk_ca(sk);
+	u32 loss_thresh  = bbr->params.loss_thresh;
+	u32 pcount, divisor, inflight_hi;
+	s32 inflight_prev, lost_prev;
+	u64 loss_budget, lost_prefix;
+
+	pcount = tcp_skb_pcount(skb);
+
+	/* How much data was in flight before this skb? */
+	inflight_prev = rs->tx_in_flight - pcount;
+	if (WARN_ONCE(inflight_prev < 0,
+		      "tx_in_flight: %u pcount: %u reneg: %u",
+		      rs->tx_in_flight, pcount, tcp_sk(sk)->is_sack_reneg))
+		return ~0U;
+
+	/* How much inflight data was marked lost before this skb? */
+	lost_prev = rs->lost - pcount;
+	if (WARN_ON_ONCE(lost_prev < 0))
+		return ~0U;
+
+	/* At what prefix of this lost skb did losss rate exceed loss_thresh? */
+	loss_budget = (u64)inflight_prev * loss_thresh + BBR_UNIT - 1;
+	loss_budget >>= BBR_SCALE;
+	if (lost_prev >= loss_budget) {
+		lost_prefix = 0;   /* previous losses crossed loss_thresh */
+	} else {
+		lost_prefix = loss_budget - lost_prev;
+		lost_prefix <<= BBR_SCALE;
+		divisor = BBR_UNIT - loss_thresh;
+		if (WARN_ON_ONCE(!divisor))  /* loss_thresh is 8 bits */
+			return ~0U;
+		do_div(lost_prefix, divisor);
+	}
+
+	inflight_hi = inflight_prev + lost_prefix;
+	return inflight_hi;
+}
+
+/* If loss/ECN rates during probing indicated we may have overfilled a
+ * buffer, return an operating point that tries to leave unutilized headroom in
+ * the path for other flows, for fairness convergence and lower RTTs and loss.
+ */
+static u32 bbr2_inflight_with_headroom(const struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 headroom, headroom_fraction;
+
+	if (bbr->inflight_hi == ~0U)
+		return ~0U;
+
+	headroom_fraction = bbr->params.inflight_headroom;
+	headroom = ((u64)bbr->inflight_hi * headroom_fraction) >> BBR_SCALE;
+	headroom = max(headroom, 1U);
+	return max_t(s32, bbr->inflight_hi - headroom,
+		     bbr->params.cwnd_min_target);
+}
+
+/* Bound cwnd to a sensible level, based on our current probing state
+ * machine phase and model of a good inflight level (inflight_lo, inflight_hi).
+ */
+static void bbr2_bound_cwnd_for_inflight_model(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 cap;
+
+	/* tcp_rcv_synsent_state_process() currently calls tcp_ack()
+	 * and thus cong_control() without first initializing us(!).
+	 */
+	if (!bbr->initialized)
+		return;
+
+	cap = ~0U;
+	if (bbr->mode == BBR_PROBE_BW &&
+	    bbr->cycle_idx != BBR_BW_PROBE_CRUISE) {
+		/* Probe to see if more packets fit in the path. */
+		cap = bbr->inflight_hi;
+	} else {
+		if (bbr->mode == BBR_PROBE_RTT ||
+		    (bbr->mode == BBR_PROBE_BW &&
+		     bbr->cycle_idx == BBR_BW_PROBE_CRUISE))
+			cap = bbr2_inflight_with_headroom(sk);
+	}
+	/* Adapt to any loss/ECN since our last bw probe. */
+	cap = min(cap, bbr->inflight_lo);
+
+	cap = max_t(u32, cap, bbr->params.cwnd_min_target);
+	tp->snd_cwnd = min(cap, tp->snd_cwnd);
+}
+
+/* Estimate a short-term lower bound on the capacity available now, based
+ * on measurements of the current delivery process and recent history. When we
+ * are seeing loss/ECN at times when we are not probing bw, then conservatively
+ * move toward flow balance by multiplicatively cutting our short-term
+ * estimated safe rate and volume of data (bw_lo and inflight_lo). We use a
+ * multiplicative decrease in order to converge to a lower capacity in time
+ * logarithmic in the magnitude of the decrease.
+ *
+ * However, we do not cut our short-term estimates lower than the current rate
+ * and volume of delivered data from this round trip, since from the current
+ * delivery process we can estimate the measured capacity available now.
+ *
+ * Anything faster than that approach would knowingly risk high loss, which can
+ * cause low bw for Reno/CUBIC and high loss recovery latency for
+ * request/response flows using any congestion control.
+ */
+static void bbr2_adapt_lower_bounds(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 ecn_cut, ecn_inflight_lo, beta;
+
+	/* We only use lower-bound estimates when not probing bw.
+	 * When probing we need to push inflight higher to probe bw.
+	 */
+	if (bbr2_is_probing_bandwidth(sk))
+		return;
+
+	/* ECN response. */
+	if (bbr->ecn_in_round && bbr->ecn_eligible && bbr->params.ecn_factor) {
+		/* Reduce inflight to (1 - alpha*ecn_factor). */
+		ecn_cut = (BBR_UNIT -
+			   ((bbr->ecn_alpha * bbr->params.ecn_factor) >>
+			    BBR_SCALE));
+		if (bbr->inflight_lo == ~0U)
+			bbr->inflight_lo = tp->snd_cwnd;
+		ecn_inflight_lo = (u64)bbr->inflight_lo * ecn_cut >> BBR_SCALE;
+	} else {
+		ecn_inflight_lo = ~0U;
+	}
+
+	/* Loss response. */
+	if (bbr->loss_in_round) {
+		/* Reduce bw and inflight to (1 - beta). */
+		if (bbr->bw_lo == ~0U)
+			bbr->bw_lo = bbr_max_bw(sk);
+		if (bbr->inflight_lo == ~0U)
+			bbr->inflight_lo = tp->snd_cwnd;
+		beta = bbr->params.beta;
+		bbr->bw_lo =
+			max_t(u32, bbr->bw_latest,
+			      (u64)bbr->bw_lo *
+			      (BBR_UNIT - beta) >> BBR_SCALE);
+		bbr->inflight_lo =
+			max_t(u32, bbr->inflight_latest,
+			      (u64)bbr->inflight_lo *
+			      (BBR_UNIT - beta) >> BBR_SCALE);
+	}
+
+	/* Adjust to the lower of the levels implied by loss or ECN. */
+	bbr->inflight_lo = min(bbr->inflight_lo, ecn_inflight_lo);
+}
+
+/* Reset any short-term lower-bound adaptation to congestion, so that we can
+ * push our inflight up.
+ */
+static void bbr2_reset_lower_bounds(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->bw_lo = ~0U;
+	bbr->inflight_lo = ~0U;
+}
+
+/* After bw probing (STARTUP/PROBE_UP), reset signals before entering a state
+ * machine phase where we adapt our lower bound based on congestion signals.
+ */
+static void bbr2_reset_congestion_signals(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->loss_in_round = 0;
+	bbr->ecn_in_round = 0;
+	bbr->loss_in_cycle = 0;
+	bbr->ecn_in_cycle = 0;
+	bbr->bw_latest = 0;
+	bbr->inflight_latest = 0;
+}
+
+/* Update (most of) our congestion signals: track the recent rate and volume of
+ * delivered data, presence of loss, and EWMA degree of ECN marking.
+ */
+static void bbr2_update_congestion_signals(
+	struct sock *sk, const struct rate_sample *rs, struct bbr_context *ctx)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	u64 bw;
+
+	bbr->loss_round_start = 0;
+	if (rs->interval_us <= 0 || !rs->acked_sacked)
+		return; /* Not a valid observation */
+	bw = ctx->sample_bw;
+
+	if (!rs->is_app_limited || bw >= bbr_max_bw(sk))
+		bbr2_take_bw_hi_sample(sk, bw);
+
+	bbr->loss_in_round |= (rs->losses > 0);
+
+	/* Update rate and volume of delivered data from latest round trip: */
+	bbr->bw_latest       = max_t(u32, bbr->bw_latest,       ctx->sample_bw);
+	bbr->inflight_latest = max_t(u32, bbr->inflight_latest, rs->delivered);
+
+	if (before(rs->prior_delivered, bbr->loss_round_delivered))
+		return;		/* skip the per-round-trip updates */
+	/* Now do per-round-trip updates. */
+	bbr->loss_round_delivered = tp->delivered;  /* mark round trip */
+	bbr->loss_round_start = 1;
+	bbr2_adapt_lower_bounds(sk);
+
+	/* Update windowed "latest" (single-round-trip) filters. */
+	bbr->loss_in_round = 0;
+	bbr->ecn_in_round  = 0;
+	bbr->bw_latest = ctx->sample_bw;
+	bbr->inflight_latest = rs->delivered;
+}
+
+/* Bandwidth probing can cause loss. To help coexistence with loss-based
+ * congestion control we spread out our probing in a Reno-conscious way. Due to
+ * the shape of the Reno sawtooth, the time required between loss epochs for an
+ * idealized Reno flow is a number of round trips that is the BDP of that
+ * flow. We count packet-timed round trips directly, since measured RTT can
+ * vary widely, and Reno is driven by packet-timed round trips.
+ */
+static bool bbr2_is_reno_coexistence_probe_time(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 inflight, rounds, reno_gain, reno_rounds;
+
+	/* Random loss can shave some small percentage off of our inflight
+	 * in each round. To survive this, flows need robust periodic probes.
+	 */
+	rounds = bbr->params.bw_probe_max_rounds;
+
+	reno_gain = bbr->params.bw_probe_reno_gain;
+	if (reno_gain) {
+		inflight = bbr2_target_inflight(sk);
+		reno_rounds = ((u64)inflight * reno_gain) >> BBR_SCALE;
+		rounds = min(rounds, reno_rounds);
+	}
+	return bbr->rounds_since_probe >= rounds;
+}
+
+/* How long do we want to wait before probing for bandwidth (and risking
+ * loss)? We randomize the wait, for better mixing and fairness convergence.
+ *
+ * We bound the Reno-coexistence inter-bw-probe time to be 62-63 round trips.
+ * This is calculated to allow fairness with a 25Mbps, 30ms Reno flow,
+ * (eg 4K video to a broadband user):
+ *   BDP = 25Mbps * .030sec /(1514bytes) = 61.9 packets
+ *
+ * We bound the BBR-native inter-bw-probe wall clock time to be:
+ *  (a) higher than 2 sec: to try to avoid causing loss for a long enough time
+ *      to allow Reno at 30ms to get 4K video bw, the inter-bw-probe time must
+ *      be at least: 25Mbps * .030sec / (1514bytes) * 0.030sec = 1.9secs
+ *  (b) lower than 3 sec: to ensure flows can start probing in a reasonable
+ *      amount of time to discover unutilized bw on human-scale interactive
+ *      time-scales (e.g. perhaps traffic from a web page download that we
+ *      were competing with is now complete).
+ */
+static void bbr2_pick_probe_wait(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	/* Decide the random round-trip bound for wait until probe: */
+	bbr->rounds_since_probe =
+		get_random_u32_below(bbr->params.bw_probe_rand_rounds);
+	/* Decide the random wall clock bound for wait until probe: */
+	bbr->probe_wait_us = bbr->params.bw_probe_base_us +
+			     get_random_u32_below(bbr->params.bw_probe_rand_us);
+}
+
+static void bbr2_set_cycle_idx(struct sock *sk, int cycle_idx)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->cycle_idx = cycle_idx;
+	/* New phase, so need to update cwnd and pacing rate. */
+	bbr->try_fast_path = 0;
+}
+
+/* Send at estimated bw to fill the pipe, but not queue. We need this phase
+ * before PROBE_UP, because as soon as we send faster than the available bw
+ * we will start building a queue, and if the buffer is shallow we can cause
+ * loss. If we do not fill the pipe before we cause this loss, our bw_hi and
+ * inflight_hi estimates will underestimate.
+ */
+static void bbr2_start_bw_probe_refill(struct sock *sk, u32 bw_probe_up_rounds)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr2_reset_lower_bounds(sk);
+	if (bbr->inflight_hi != ~0U)
+		bbr->inflight_hi += bbr->params.refill_add_inc;
+	bbr->bw_probe_up_rounds = bw_probe_up_rounds;
+	bbr->bw_probe_up_acks = 0;
+	bbr->stopped_risky_probe = 0;
+	bbr->ack_phase = BBR_ACKS_REFILLING;
+	bbr->next_rtt_delivered = tp->delivered;
+	bbr2_set_cycle_idx(sk, BBR_BW_PROBE_REFILL);
+}
+
+/* Now probe max deliverable data rate and volume. */
+static void bbr2_start_bw_probe_up(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->ack_phase = BBR_ACKS_PROBE_STARTING;
+	bbr->next_rtt_delivered = tp->delivered;
+	bbr->cycle_mstamp = tp->tcp_mstamp;
+	bbr2_set_cycle_idx(sk, BBR_BW_PROBE_UP);
+	bbr2_raise_inflight_hi_slope(sk);
+}
+
+/* Start a new PROBE_BW probing cycle of some wall clock length. Pick a wall
+ * clock time at which to probe beyond an inflight that we think to be
+ * safe. This will knowingly risk packet loss, so we want to do this rarely, to
+ * keep packet loss rates low. Also start a round-trip counter, to probe faster
+ * if we estimate a Reno flow at our BDP would probe faster.
+ */
+static void bbr2_start_bw_probe_down(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr2_reset_congestion_signals(sk);
+	bbr->bw_probe_up_cnt = ~0U;     /* not growing inflight_hi any more */
+	bbr2_pick_probe_wait(sk);
+	bbr->cycle_mstamp = tp->tcp_mstamp;		/* start wall clock */
+	bbr->ack_phase = BBR_ACKS_PROBE_STOPPING;
+	bbr->next_rtt_delivered = tp->delivered;
+	bbr2_set_cycle_idx(sk, BBR_BW_PROBE_DOWN);
+}
+
+/* Cruise: maintain what we estimate to be a neutral, conservative
+ * operating point, without attempting to probe up for bandwidth or down for
+ * RTT, and only reducing inflight in response to loss/ECN signals.
+ */
+static void bbr2_start_bw_probe_cruise(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr->inflight_lo != ~0U)
+		bbr->inflight_lo = min(bbr->inflight_lo, bbr->inflight_hi);
+
+	bbr2_set_cycle_idx(sk, BBR_BW_PROBE_CRUISE);
+}
+
+/* Loss and/or ECN rate is too high while probing.
+ * Adapt (once per bw probe) by cutting inflight_hi and then restarting cycle.
+ */
+static void bbr2_handle_inflight_too_high(struct sock *sk,
+					  const struct rate_sample *rs)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	const u32 beta = bbr->params.beta;
+
+	bbr->prev_probe_too_high = 1;
+	bbr->bw_probe_samples = 0;  /* only react once per probe */
+	bbr->debug.event = 'L';     /* Loss/ECN too high */
+	/* If we are app-limited then we are not robustly
+	 * probing the max volume of inflight data we think
+	 * might be safe (analogous to how app-limited bw
+	 * samples are not known to be robustly probing bw).
+	 */
+	if (!rs->is_app_limited)
+		bbr->inflight_hi = max_t(u32, rs->tx_in_flight,
+					 (u64)bbr2_target_inflight(sk) *
+					 (BBR_UNIT - beta) >> BBR_SCALE);
+	if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == BBR_BW_PROBE_UP)
+		bbr2_start_bw_probe_down(sk);
+}
+
+/* If we're seeing bw and loss samples reflecting our bw probing, adapt
+ * using the signals we see. If loss or ECN mark rate gets too high, then adapt
+ * inflight_hi downward. If we're able to push inflight higher without such
+ * signals, push higher: adapt inflight_hi upward.
+ */
+static bool bbr2_adapt_upper_bounds(struct sock *sk,
+				   const struct rate_sample *rs)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	/* Track when we'll see bw/loss samples resulting from our bw probes. */
+	if (bbr->ack_phase == BBR_ACKS_PROBE_STARTING && bbr->round_start)
+		bbr->ack_phase = BBR_ACKS_PROBE_FEEDBACK;
+	if (bbr->ack_phase == BBR_ACKS_PROBE_STOPPING && bbr->round_start) {
+		/* End of samples from bw probing phase. */
+		bbr->bw_probe_samples = 0;
+		bbr->ack_phase = BBR_ACKS_INIT;
+		/* At this point in the cycle, our current bw sample is also
+		 * our best recent chance at finding the highest available bw
+		 * for this flow. So now is the best time to forget the bw
+		 * samples from the previous cycle, by advancing the window.
+		 */
+		if (bbr->mode == BBR_PROBE_BW && !rs->is_app_limited)
+			bbr2_advance_bw_hi_filter(sk);
+		/* If we had an inflight_hi, then probed and pushed inflight all
+		 * the way up to hit that inflight_hi without seeing any
+		 * high loss/ECN in all the resulting ACKs from that probing,
+		 * then probe up again, this time letting inflight persist at
+		 * inflight_hi for a round trip, then accelerating beyond.
+		 */
+		if (bbr->mode == BBR_PROBE_BW &&
+		    bbr->stopped_risky_probe && !bbr->prev_probe_too_high) {
+			bbr->debug.event = 'R';  /* reprobe */
+			bbr2_start_bw_probe_refill(sk, 0);
+			return true;  /* yes, decided state transition */
+		}
+	}
+
+	if (bbr2_is_inflight_too_high(sk, rs)) {
+		if (bbr->bw_probe_samples)  /*  sample is from bw probing? */
+			bbr2_handle_inflight_too_high(sk, rs);
+	} else {
+		/* Loss/ECN rate is declared safe. Adjust upper bound upward. */
+		if (bbr->inflight_hi == ~0U)  /* no excess queue signals yet? */
+			return false;
+
+		/* To be resilient to random loss, we must raise inflight_hi
+		 * if we observe in any phase that a higher level is safe.
+		 */
+		if (rs->tx_in_flight > bbr->inflight_hi) {
+			bbr->inflight_hi = rs->tx_in_flight;
+			bbr->debug.event = 'U';  /* raise up inflight_hi */
+		}
+
+		if (bbr->mode == BBR_PROBE_BW &&
+		    bbr->cycle_idx == BBR_BW_PROBE_UP)
+			bbr2_probe_inflight_hi_upward(sk, rs);
+	}
+
+	return false;
+}
+
+/* Check if it's time to probe for bandwidth now, and if so, kick it off. */
+static bool bbr2_check_time_to_probe_bw(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 n;
+
+	/* If we seem to be at an operating point where we are not seeing loss
+	 * but we are seeing ECN marks, then when the ECN marks cease we reprobe
+	 * quickly (in case a burst of cross-traffic has ceased and freed up bw,
+	 * or in case we are sharing with multiplicatively probing traffic).
+	 */
+	if (bbr->params.ecn_reprobe_gain && bbr->ecn_eligible &&
+	    bbr->ecn_in_cycle && !bbr->loss_in_cycle &&
+	    inet_csk(sk)->icsk_ca_state == TCP_CA_Open) {
+		bbr->debug.event = 'A';  /* *A*ll clear to probe *A*gain */
+		/* Calculate n so that when bbr2_raise_inflight_hi_slope()
+		 * computes growth_this_round as 2^n it will be roughly the
+		 * desired volume of data (inflight_hi*ecn_reprobe_gain).
+		 */
+		n = ilog2((((u64)bbr->inflight_hi *
+			    bbr->params.ecn_reprobe_gain) >> BBR_SCALE));
+		bbr2_start_bw_probe_refill(sk, n);
+		return true;
+	}
+
+	if (bbr2_has_elapsed_in_phase(sk, bbr->probe_wait_us) ||
+	    bbr2_is_reno_coexistence_probe_time(sk)) {
+		bbr2_start_bw_probe_refill(sk, 0);
+		return true;
+	}
+	return false;
+}
+
+/* Is it time to transition from PROBE_DOWN to PROBE_CRUISE? */
+static bool bbr2_check_time_to_cruise(struct sock *sk, u32 inflight, u32 bw)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	bool is_under_bdp, is_long_enough;
+
+	/* Always need to pull inflight down to leave headroom in queue. */
+	if (inflight > bbr2_inflight_with_headroom(sk))
+		return false;
+
+	is_under_bdp = inflight <= bbr_inflight(sk, bw, BBR_UNIT);
+	if (bbr->params.drain_to_target)
+		return is_under_bdp;
+
+	is_long_enough = bbr2_has_elapsed_in_phase(sk, bbr->min_rtt_us);
+	return is_under_bdp || is_long_enough;
+}
+
+/* PROBE_BW state machine: cruise, refill, probe for bw, or drain? */
+static void bbr2_update_cycle_phase(struct sock *sk,
+				    const struct rate_sample *rs)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	bool is_risky = false, is_queuing = false;
+	u32 inflight, bw;
+
+	if (!bbr_full_bw_reached(sk))
+		return;
+
+	/* In DRAIN, PROBE_BW, or PROBE_RTT, adjust upper bounds. */
+	if (bbr2_adapt_upper_bounds(sk, rs))
+		return;		/* already decided state transition */
+
+	if (bbr->mode != BBR_PROBE_BW)
+		return;
+
+	inflight = bbr_packets_in_net_at_edt(sk, rs->prior_in_flight);
+	bw = bbr_max_bw(sk);
+
+	switch (bbr->cycle_idx) {
+	/* First we spend most of our time cruising with a pacing_gain of 1.0,
+	 * which paces at the estimated bw, to try to fully use the pipe
+	 * without building queue. If we encounter loss/ECN marks, we adapt
+	 * by slowing down.
+	 */
+	case BBR_BW_PROBE_CRUISE:
+		if (bbr2_check_time_to_probe_bw(sk))
+			return;		/* already decided state transition */
+		break;
+
+	/* After cruising, when it's time to probe, we first "refill": we send
+	 * at the estimated bw to fill the pipe, before probing higher and
+	 * knowingly risking overflowing the bottleneck buffer (causing loss).
+	 */
+	case BBR_BW_PROBE_REFILL:
+		if (bbr->round_start) {
+			/* After one full round trip of sending in REFILL, we
+			 * start to see bw samples reflecting our REFILL, which
+			 * may be putting too much data in flight.
+			 */
+			bbr->bw_probe_samples = 1;
+			bbr2_start_bw_probe_up(sk);
+		}
+		break;
+
+	/* After we refill the pipe, we probe by using a pacing_gain > 1.0, to
+	 * probe for bw. If we have not seen loss/ECN, we try to raise inflight
+	 * to at least pacing_gain*BDP; note that this may take more than
+	 * min_rtt if min_rtt is small (e.g. on a LAN).
+	 *
+	 * We terminate PROBE_UP bandwidth probing upon any of the following:
+	 *
+	 * (1) We've pushed inflight up to hit the inflight_hi target set in the
+	 *     most recent previous bw probe phase. Thus we want to start
+	 *     draining the queue immediately because it's very likely the most
+	 *     recently sent packets will fill the queue and cause drops.
+	 *     (checked here)
+	 * (2) We have probed for at least 1*min_rtt_us, and the
+	 *     estimated queue is high enough (inflight > 1.25 * estimated_bdp).
+	 *     (checked here)
+	 * (3) Loss filter says loss rate is "too high".
+	 *     (checked in bbr_is_inflight_too_high())
+	 * (4) ECN filter says ECN mark rate is "too high".
+	 *     (checked in bbr_is_inflight_too_high())
+	 */
+	case BBR_BW_PROBE_UP:
+		if (bbr->prev_probe_too_high &&
+		    inflight >= bbr->inflight_hi) {
+			bbr->stopped_risky_probe = 1;
+			is_risky = true;
+			bbr->debug.event = 'D';   /* D for danger */
+		} else if (bbr2_has_elapsed_in_phase(sk, bbr->min_rtt_us) &&
+			   inflight >=
+			   bbr_inflight(sk, bw,
+					bbr->params.bw_probe_pif_gain)) {
+			is_queuing = true;
+			bbr->debug.event = 'Q'; /* building Queue */
+		}
+		if (is_risky || is_queuing) {
+			bbr->prev_probe_too_high = 0;  /* no loss/ECN (yet) */
+			bbr2_start_bw_probe_down(sk);  /* restart w/ down */
+		}
+		break;
+
+	/* After probing in PROBE_UP, we have usually accumulated some data in
+	 * the bottleneck buffer (if bw probing didn't find more bw). We next
+	 * enter PROBE_DOWN to try to drain any excess data from the queue. To
+	 * do this, we use a pacing_gain < 1.0. We hold this pacing gain until
+	 * our inflight is less then that target cruising point, which is the
+	 * minimum of (a) the amount needed to leave headroom, and (b) the
+	 * estimated BDP. Once inflight falls to match the target, we estimate
+	 * the queue is drained; persisting would underutilize the pipe.
+	 */
+	case BBR_BW_PROBE_DOWN:
+		if (bbr2_check_time_to_probe_bw(sk))
+			return;		/* already decided state transition */
+		if (bbr2_check_time_to_cruise(sk, inflight, bw))
+			bbr2_start_bw_probe_cruise(sk);
+		break;
+
+	default:
+		WARN_ONCE(1, "BBR invalid cycle index %u\n", bbr->cycle_idx);
+	}
+}
+
+/* Exiting PROBE_RTT, so return to bandwidth probing in STARTUP or PROBE_BW. */
+static void bbr2_exit_probe_rtt(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr2_reset_lower_bounds(sk);
+	if (bbr_full_bw_reached(sk)) {
+		bbr->mode = BBR_PROBE_BW;
+		/* Raising inflight after PROBE_RTT may cause loss, so reset
+		 * the PROBE_BW clock and schedule the next bandwidth probe for
+		 * a friendly and randomized future point in time.
+		 */
+		bbr2_start_bw_probe_down(sk);
+		/* Since we are exiting PROBE_RTT, we know inflight is
+		 * below our estimated BDP, so it is reasonable to cruise.
+		 */
+		bbr2_start_bw_probe_cruise(sk);
+	} else {
+		bbr->mode = BBR_STARTUP;
+	}
+}
+
+/* Exit STARTUP based on loss rate > 1% and loss gaps in round >= N. Wait until
+ * the end of the round in recovery to get a good estimate of how many packets
+ * have been lost, and how many we need to drain with a low pacing rate.
+ */
+static void bbr2_check_loss_too_high_in_startup(struct sock *sk,
+					       const struct rate_sample *rs)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr_full_bw_reached(sk))
+		return;
+
+	/* For STARTUP exit, check the loss rate at the end of each round trip
+	 * of Recovery episodes in STARTUP. We check the loss rate at the end
+	 * of the round trip to filter out noisy/low loss and have a better
+	 * sense of inflight (extent of loss), so we can drain more accurately.
+	 */
+	if (rs->losses && bbr->loss_events_in_round < 0xf)
+		bbr->loss_events_in_round++;  /* update saturating counter */
+	if (bbr->params.full_loss_cnt && bbr->loss_round_start &&
+	    inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery &&
+	    bbr->loss_events_in_round >= bbr->params.full_loss_cnt &&
+	    bbr2_is_inflight_too_high(sk, rs)) {
+		bbr->debug.event = 'P';  /* Packet loss caused STARTUP exit */
+		bbr2_handle_queue_too_high_in_startup(sk);
+		return;
+	}
+	if (bbr->loss_round_start)
+		bbr->loss_events_in_round = 0;
+}
+
+/* If we are done draining, advance into steady state operation in PROBE_BW. */
+static void bbr2_check_drain(struct sock *sk, const struct rate_sample *rs,
+			     struct bbr_context *ctx)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (bbr_check_drain(sk, rs, ctx)) {
+		bbr->mode = BBR_PROBE_BW;
+		bbr2_start_bw_probe_down(sk);
+	}
+}
+
+static void bbr2_update_model(struct sock *sk, const struct rate_sample *rs,
+			      struct bbr_context *ctx)
+{
+	bbr2_update_congestion_signals(sk, rs, ctx);
+	bbr_update_ack_aggregation(sk, rs);
+	bbr2_check_loss_too_high_in_startup(sk, rs);
+	bbr_check_full_bw_reached(sk, rs);
+	bbr2_check_drain(sk, rs, ctx);
+	bbr2_update_cycle_phase(sk, rs);
+	bbr_update_min_rtt(sk, rs);
+}
+
+/* Fast path for app-limited case.
+ *
+ * On each ack, we execute bbr state machine, which primarily consists of:
+ * 1) update model based on new rate sample, and
+ * 2) update control based on updated model or state change.
+ *
+ * There are certain workload/scenarios, e.g. app-limited case, where
+ * either we can skip updating model or we can skip update of both model
+ * as well as control. This provides signifcant softirq cpu savings for
+ * processing incoming acks.
+ *
+ * In case of app-limited, if there is no congestion (loss/ecn) and
+ * if observed bw sample is less than current estimated bw, then we can
+ * skip some of the computation in bbr state processing:
+ *
+ * - if there is no rtt/mode/phase change: In this case, since all the
+ *   parameters of the network model are constant, we can skip model
+ *   as well control update.
+ *
+ * - else we can skip rest of the model update. But we still need to
+ *   update the control to account for the new rtt/mode/phase.
+ *
+ * Returns whether we can take fast path or not.
+ */
+static bool bbr2_fast_path(struct sock *sk, bool *update_model,
+		const struct rate_sample *rs, struct bbr_context *ctx)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	u32 prev_min_rtt_us, prev_mode;
+
+	if (bbr->params.fast_path && bbr->try_fast_path &&
+	    rs->is_app_limited && ctx->sample_bw < bbr_max_bw(sk) &&
+	    !bbr->loss_in_round && !bbr->ecn_in_round) {
+		prev_mode = bbr->mode;
+		prev_min_rtt_us = bbr->min_rtt_us;
+		bbr2_check_drain(sk, rs, ctx);
+		bbr2_update_cycle_phase(sk, rs);
+		bbr_update_min_rtt(sk, rs);
+
+		if (bbr->mode == prev_mode &&
+		    bbr->min_rtt_us == prev_min_rtt_us &&
+		    bbr->try_fast_path)
+			return true;
+
+		/* Skip model update, but control still needs to be updated */
+		*update_model = false;
+	}
+	return false;
+}
+
+static void bbr2_main(struct sock *sk, const struct rate_sample *rs)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	struct bbr_context ctx = { 0 };
+	bool update_model = true;
+	u32 bw;
+
+	bbr->debug.event = '.';  /* init to default NOP (no event yet) */
+
+	bbr_update_round_start(sk, rs, &ctx);
+	if (bbr->round_start) {
+		bbr->rounds_since_probe =
+			min_t(s32, bbr->rounds_since_probe + 1, 0xFF);
+		bbr2_update_ecn_alpha(sk);
+	}
+
+	bbr->ecn_in_round  |= rs->is_ece;
+	bbr_calculate_bw_sample(sk, rs, &ctx);
+
+	if (bbr2_fast_path(sk, &update_model, rs, &ctx))
+		goto out;
+
+	if (update_model)
+		bbr2_update_model(sk, rs, &ctx);
+
+	bbr_update_gains(sk);
+	bw = bbr_bw(sk);
+	bbr_set_pacing_rate(sk, bw, bbr->pacing_gain);
+	bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain,
+		     tp->snd_cwnd, &ctx);
+	bbr2_bound_cwnd_for_inflight_model(sk);
+
+out:
+	bbr->prev_ca_state = inet_csk(sk)->icsk_ca_state;
+	bbr->loss_in_cycle |= rs->lost > 0;
+	bbr->ecn_in_cycle  |= rs->delivered_ce > 0;
+
+	bbr_debug(sk, rs->acked_sacked, rs, &ctx);
+}
+
+/* Module parameters that are settable by TCP_CONGESTION_PARAMS are declared
+ * down here, so that the algorithm functions that use the parameters must use
+ * the per-socket parameters; if they accidentally use the global version
+ * then there will be a compile error.
+ * TODO(ncardwell): move all per-socket parameters down to this section.
+ */
+
+/* On losses, scale down inflight and pacing rate by beta scaled by BBR_SCALE.
+ * No loss response when 0. Max allwed value is 255.
+ */
+static u32 bbr_beta = BBR_UNIT * 30 / 100;
+
+/* Gain factor for ECN mark ratio samples, scaled by BBR_SCALE.
+ * Max allowed value is 255.
+ */
+static u32 bbr_ecn_alpha_gain = BBR_UNIT * 1 / 16;  /* 1/16 = 6.25% */
+
+/* The initial value for the ecn_alpha state variable. Default and max
+ * BBR_UNIT (256), representing 1.0. This allows a flow to respond quickly
+ * to congestion if the bottleneck is congested when the flow starts up.
+ */
+static u32 bbr_ecn_alpha_init = BBR_UNIT;	/* 1.0, to respond quickly */
+
+/* On ECN, cut inflight_lo to (1 - ecn_factor * ecn_alpha) scaled by BBR_SCALE.
+ * No ECN based bounding when 0. Max allwed value is 255.
+ */
+static u32 bbr_ecn_factor = BBR_UNIT * 1 / 3;	    /* 1/3 = 33% */
+
+/* Estimate bw probing has gone too far if CE ratio exceeds this threshold.
+ * Scaled by BBR_SCALE. Disabled when 0. Max allowed is 255.
+ */
+static u32 bbr_ecn_thresh = BBR_UNIT * 1 / 2;  /* 1/2 = 50% */
+
+/* Max RTT (in usec) at which to use sender-side ECN logic.
+ * Disabled when 0 (ECN allowed at any RTT).
+ * Max allowed for the parameter is 524287 (0x7ffff) us, ~524 ms.
+ */
+static u32 bbr_ecn_max_rtt_us = 5000;
+
+/* If non-zero, if in a cycle with no losses but some ECN marks, after ECN
+ * clears then use a multiplicative increase to quickly reprobe bw by
+ * starting inflight probing at the given multiple of inflight_hi.
+ * Default for this experimental knob is 0 (disabled).
+ * Planned value for experiments: BBR_UNIT * 1 / 2 = 128, representing 0.5.
+ */
+static u32 bbr_ecn_reprobe_gain;
+
+/* Estimate bw probing has gone too far if loss rate exceeds this level. */
+static u32 bbr_loss_thresh = BBR_UNIT * 2 / 100;  /* 2% loss */
+
+/* Exit STARTUP if number of loss marking events in a Recovery round is >= N,
+ * and loss rate is higher than bbr_loss_thresh.
+ * Disabled if 0. Max allowed value is 15 (0xF).
+ */
+static u32 bbr_full_loss_cnt = 8;
+
+/* Exit STARTUP if number of round trips with ECN mark rate above ecn_thresh
+ * meets this count. Max allowed value is 3.
+ */
+static u32 bbr_full_ecn_cnt = 2;
+
+/* Fraction of unutilized headroom to try to leave in path upon high loss. */
+static u32 bbr_inflight_headroom = BBR_UNIT * 15 / 100;
+
+/* Multiplier to get target inflight (as multiple of BDP) for PROBE_UP phase.
+ * Default is 1.25x, as in BBR v1. Max allowed is 511.
+ */
+static u32 bbr_bw_probe_pif_gain = BBR_UNIT * 5 / 4;
+
+/* Multiplier to get Reno-style probe epoch duration as: k * BDP round trips.
+ * If zero, disables this BBR v2 Reno-style BDP-scaled coexistence mechanism.
+ * Max allowed is 511.
+ */
+static u32 bbr_bw_probe_reno_gain = BBR_UNIT;
+
+/* Max number of packet-timed rounds to wait before probing for bandwidth.  If
+ * we want to tolerate 1% random loss per round, and not have this cut our
+ * inflight too much, we must probe for bw periodically on roughly this scale.
+ * If low, limits Reno/CUBIC coexistence; if high, limits loss tolerance.
+ * We aim to be fair with Reno/CUBIC up to a BDP of at least:
+ *  BDP = 25Mbps * .030sec /(1514bytes) = 61.9 packets
+ */
+static u32 bbr_bw_probe_max_rounds = 63;
+
+/* Max amount of randomness to inject in round counting for Reno-coexistence.
+ * Max value is 15.
+ */
+static u32 bbr_bw_probe_rand_rounds = 2;
+
+/* Use BBR-native probe time scale starting at this many usec.
+ * We aim to be fair with Reno/CUBIC up to an inter-loss time epoch of at least:
+ *  BDP*RTT = 25Mbps * .030sec /(1514bytes) * 0.030sec = 1.9 secs
+ */
+static u32 bbr_bw_probe_base_us = 2 * USEC_PER_SEC;  /* 2 secs */
+
+/* Use BBR-native probes spread over this many usec: */
+static u32 bbr_bw_probe_rand_us = 1 * USEC_PER_SEC;  /* 1 secs */
+
+/* Undo the model changes made in loss recovery if recovery was spurious? */
+static bool bbr_undo = true;
+
+/* Use fast path if app-limited, no loss/ECN, and target cwnd was reached? */
+static bool bbr_fast_path = true;	/* default: enabled */
+
+/* Use fast ack mode ? */
+static int bbr_fast_ack_mode = 1;	/* default: rwnd check off */
+
+/* How much to additively increase inflight_hi when entering REFILL? */
+static u32 bbr_refill_add_inc;		/* default: disabled */
+
+module_param_named(beta,                 bbr_beta,                 uint, 0644);
+module_param_named(ecn_alpha_gain,       bbr_ecn_alpha_gain,       uint, 0644);
+module_param_named(ecn_alpha_init,       bbr_ecn_alpha_init,       uint, 0644);
+module_param_named(ecn_factor,           bbr_ecn_factor,           uint, 0644);
+module_param_named(ecn_thresh,           bbr_ecn_thresh,           uint, 0644);
+module_param_named(ecn_max_rtt_us,       bbr_ecn_max_rtt_us,       uint, 0644);
+module_param_named(ecn_reprobe_gain,     bbr_ecn_reprobe_gain,     uint, 0644);
+module_param_named(loss_thresh,          bbr_loss_thresh,          uint, 0664);
+module_param_named(full_loss_cnt,        bbr_full_loss_cnt,        uint, 0664);
+module_param_named(full_ecn_cnt,         bbr_full_ecn_cnt,         uint, 0664);
+module_param_named(inflight_headroom,    bbr_inflight_headroom,    uint, 0664);
+module_param_named(bw_probe_pif_gain,    bbr_bw_probe_pif_gain,    uint, 0664);
+module_param_named(bw_probe_reno_gain,   bbr_bw_probe_reno_gain,   uint, 0664);
+module_param_named(bw_probe_max_rounds,  bbr_bw_probe_max_rounds,  uint, 0664);
+module_param_named(bw_probe_rand_rounds, bbr_bw_probe_rand_rounds, uint, 0664);
+module_param_named(bw_probe_base_us,     bbr_bw_probe_base_us,     uint, 0664);
+module_param_named(bw_probe_rand_us,     bbr_bw_probe_rand_us,     uint, 0664);
+module_param_named(undo,                 bbr_undo,                 bool, 0664);
+module_param_named(fast_path,		 bbr_fast_path,		   bool, 0664);
+module_param_named(fast_ack_mode,	 bbr_fast_ack_mode,	   uint, 0664);
+module_param_named(refill_add_inc,       bbr_refill_add_inc,       uint, 0664);
+
+static void bbr2_init(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr_init(sk);	/* run shared init code for v1 and v2 */
+
+	/* BBR v2 parameters: */
+	bbr->params.beta = min_t(u32, 0xFFU, bbr_beta);
+	bbr->params.ecn_alpha_gain = min_t(u32, 0xFFU, bbr_ecn_alpha_gain);
+	bbr->params.ecn_alpha_init = min_t(u32, BBR_UNIT, bbr_ecn_alpha_init);
+	bbr->params.ecn_factor = min_t(u32, 0xFFU, bbr_ecn_factor);
+	bbr->params.ecn_thresh = min_t(u32, 0xFFU, bbr_ecn_thresh);
+	bbr->params.ecn_max_rtt_us = min_t(u32, 0x7ffffU, bbr_ecn_max_rtt_us);
+	bbr->params.ecn_reprobe_gain = min_t(u32, 0x1FF, bbr_ecn_reprobe_gain);
+	bbr->params.loss_thresh = min_t(u32, 0xFFU, bbr_loss_thresh);
+	bbr->params.full_loss_cnt = min_t(u32, 0xFU, bbr_full_loss_cnt);
+	bbr->params.full_ecn_cnt = min_t(u32, 0x3U, bbr_full_ecn_cnt);
+	bbr->params.inflight_headroom =
+		min_t(u32, 0xFFU, bbr_inflight_headroom);
+	bbr->params.bw_probe_pif_gain =
+		min_t(u32, 0x1FFU, bbr_bw_probe_pif_gain);
+	bbr->params.bw_probe_reno_gain =
+		min_t(u32, 0x1FFU, bbr_bw_probe_reno_gain);
+	bbr->params.bw_probe_max_rounds =
+		min_t(u32, 0xFFU, bbr_bw_probe_max_rounds);
+	bbr->params.bw_probe_rand_rounds =
+		min_t(u32, 0xFU, bbr_bw_probe_rand_rounds);
+	bbr->params.bw_probe_base_us =
+		min_t(u32, (1 << 26) - 1, bbr_bw_probe_base_us);
+	bbr->params.bw_probe_rand_us =
+		min_t(u32, (1 << 26) - 1, bbr_bw_probe_rand_us);
+	bbr->params.undo = bbr_undo;
+	bbr->params.fast_path = bbr_fast_path ? 1 : 0;
+	bbr->params.refill_add_inc = min_t(u32, 0x3U, bbr_refill_add_inc);
+
+	/* BBR v2 state: */
+	bbr->initialized = 1;
+	/* Start sampling ECN mark rate after first full flight is ACKed: */
+	bbr->loss_round_delivered = tp->delivered + 1;
+	bbr->loss_round_start = 0;
+	bbr->undo_bw_lo = 0;
+	bbr->undo_inflight_lo = 0;
+	bbr->undo_inflight_hi = 0;
+	bbr->loss_events_in_round = 0;
+	bbr->startup_ecn_rounds = 0;
+	bbr2_reset_congestion_signals(sk);
+	bbr->bw_lo = ~0U;
+	bbr->bw_hi[0] = 0;
+	bbr->bw_hi[1] = 0;
+	bbr->inflight_lo = ~0U;
+	bbr->inflight_hi = ~0U;
+	bbr->bw_probe_up_cnt = ~0U;
+	bbr->bw_probe_up_acks = 0;
+	bbr->bw_probe_up_rounds = 0;
+	bbr->probe_wait_us = 0;
+	bbr->stopped_risky_probe = 0;
+	bbr->ack_phase = BBR_ACKS_INIT;
+	bbr->rounds_since_probe = 0;
+	bbr->bw_probe_samples = 0;
+	bbr->prev_probe_too_high = 0;
+	bbr->ecn_eligible = 0;
+	bbr->ecn_alpha = bbr->params.ecn_alpha_init;
+	bbr->alpha_last_delivered = 0;
+	bbr->alpha_last_delivered_ce = 0;
+
+	tp->fast_ack_mode = min_t(u32, 0x2U, bbr_fast_ack_mode);
+
+	if ((tp->ecn_flags & TCP_ECN_OK) && bbr_ecn_enable)
+		tp->ecn_flags |= TCP_ECN_ECT_PERMANENT;
+}
+
+/* Core TCP stack informs us that the given skb was just marked lost. */
+static void bbr2_skb_marked_lost(struct sock *sk, const struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+	struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+	struct rate_sample rs;
+
+	/* Capture "current" data over the full round trip of loss,
+	 * to have a better chance to see the full capacity of the path.
+	*/
+	if (!bbr->loss_in_round)  /* first loss in this round trip? */
+		bbr->loss_round_delivered = tp->delivered;  /* set round trip */
+	bbr->loss_in_round = 1;
+	bbr->loss_in_cycle = 1;
+
+	if (!bbr->bw_probe_samples)
+		return;  /* not an skb sent while probing for bandwidth */
+	if (unlikely(!scb->tx.delivered_mstamp))
+		return;  /* skb was SACKed, reneged, marked lost; ignore it */
+	/* We are probing for bandwidth. Construct a rate sample that
+	 * estimates what happened in the flight leading up to this lost skb,
+	 * then see if the loss rate went too high, and if so at which packet.
+	 */
+	memset(&rs, 0, sizeof(rs));
+	rs.tx_in_flight = scb->tx.in_flight;
+	rs.lost = tp->lost - scb->tx.lost;
+	rs.is_app_limited = scb->tx.is_app_limited;
+	if (bbr2_is_inflight_too_high(sk, &rs)) {
+		rs.tx_in_flight = bbr2_inflight_hi_from_lost_skb(sk, &rs, skb);
+		bbr2_handle_inflight_too_high(sk, &rs);
+	}
+}
+
+/* Revert short-term model if current loss recovery event was spurious. */
+static u32 bbr2_undo_cwnd(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr->debug.undo = 1;
+	bbr->full_bw = 0;   /* spurious slow-down; reset full pipe detection */
+	bbr->full_bw_cnt = 0;
+	bbr->loss_in_round = 0;
+
+	if (!bbr->params.undo)
+		return tp->snd_cwnd;
+
+	/* Revert to cwnd and other state saved before loss episode. */
+	bbr->bw_lo = max(bbr->bw_lo, bbr->undo_bw_lo);
+	bbr->inflight_lo = max(bbr->inflight_lo, bbr->undo_inflight_lo);
+	bbr->inflight_hi = max(bbr->inflight_hi, bbr->undo_inflight_hi);
+	return bbr->prior_cwnd;
+}
+
+/* Entering loss recovery, so save state for when we undo recovery. */
+static u32 bbr2_ssthresh(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	bbr_save_cwnd(sk);
+	/* For undo, save state that adapts based on loss signal. */
+	bbr->undo_bw_lo		= bbr->bw_lo;
+	bbr->undo_inflight_lo	= bbr->inflight_lo;
+	bbr->undo_inflight_hi	= bbr->inflight_hi;
+	return tcp_sk(sk)->snd_ssthresh;
+}
+
+static enum tcp_bbr2_phase bbr2_get_phase(struct bbr *bbr)
+{
+	switch (bbr->mode) {
+	case BBR_STARTUP:
+		return BBR2_PHASE_STARTUP;
+	case BBR_DRAIN:
+		return BBR2_PHASE_DRAIN;
+	case BBR_PROBE_BW:
+		break;
+	case BBR_PROBE_RTT:
+		return BBR2_PHASE_PROBE_RTT;
+	default:
+		return BBR2_PHASE_INVALID;
+	}
+	switch (bbr->cycle_idx) {
+	case BBR_BW_PROBE_UP:
+		return BBR2_PHASE_PROBE_BW_UP;
+	case BBR_BW_PROBE_DOWN:
+		return BBR2_PHASE_PROBE_BW_DOWN;
+	case BBR_BW_PROBE_CRUISE:
+		return BBR2_PHASE_PROBE_BW_CRUISE;
+	case BBR_BW_PROBE_REFILL:
+		return BBR2_PHASE_PROBE_BW_REFILL;
+	default:
+		return BBR2_PHASE_INVALID;
+	}
+}
+
+static size_t bbr2_get_info(struct sock *sk, u32 ext, int *attr,
+			    union tcp_cc_info *info)
+{
+	if (ext & (1 << (INET_DIAG_BBRINFO - 1)) ||
+	    ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
+		struct bbr *bbr = inet_csk_ca(sk);
+		u64 bw = bbr_bw_bytes_per_sec(sk, bbr_bw(sk));
+		u64 bw_hi = bbr_bw_bytes_per_sec(sk, bbr_max_bw(sk));
+		u64 bw_lo = bbr->bw_lo == ~0U ?
+			~0ULL : bbr_bw_bytes_per_sec(sk, bbr->bw_lo);
+
+		memset(&info->bbr2, 0, sizeof(info->bbr2));
+		info->bbr2.bbr_bw_lsb		= (u32)bw;
+		info->bbr2.bbr_bw_msb		= (u32)(bw >> 32);
+		info->bbr2.bbr_min_rtt		= bbr->min_rtt_us;
+		info->bbr2.bbr_pacing_gain	= bbr->pacing_gain;
+		info->bbr2.bbr_cwnd_gain	= bbr->cwnd_gain;
+		info->bbr2.bbr_bw_hi_lsb	= (u32)bw_hi;
+		info->bbr2.bbr_bw_hi_msb	= (u32)(bw_hi >> 32);
+		info->bbr2.bbr_bw_lo_lsb	= (u32)bw_lo;
+		info->bbr2.bbr_bw_lo_msb	= (u32)(bw_lo >> 32);
+		info->bbr2.bbr_mode		= bbr->mode;
+		info->bbr2.bbr_phase		= (__u8)bbr2_get_phase(bbr);
+		info->bbr2.bbr_version		= (__u8)2;
+		info->bbr2.bbr_inflight_lo	= bbr->inflight_lo;
+		info->bbr2.bbr_inflight_hi	= bbr->inflight_hi;
+		info->bbr2.bbr_extra_acked	= bbr_extra_acked(sk);
+		*attr = INET_DIAG_BBRINFO;
+		return sizeof(info->bbr2);
+	}
+	return 0;
+}
+
+static void bbr2_set_state(struct sock *sk, u8 new_state)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct bbr *bbr = inet_csk_ca(sk);
+
+	if (new_state == TCP_CA_Loss) {
+		struct rate_sample rs = { .losses = 1 };
+		struct bbr_context ctx = { 0 };
+
+		bbr->prev_ca_state = TCP_CA_Loss;
+		bbr->full_bw = 0;
+		if (!bbr2_is_probing_bandwidth(sk) && bbr->inflight_lo == ~0U) {
+			/* bbr_adapt_lower_bounds() needs cwnd before
+			 * we suffered an RTO, to update inflight_lo:
+			 */
+			bbr->inflight_lo =
+				max(tp->snd_cwnd, bbr->prior_cwnd);
+		}
+		bbr_debug(sk, 0, &rs, &ctx);
+	} else if (bbr->prev_ca_state == TCP_CA_Loss &&
+		   new_state != TCP_CA_Loss) {
+		tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd);
+		bbr->try_fast_path = 0; /* bound cwnd using latest model */
+	}
+}
+
+static struct tcp_congestion_ops tcp_bbr2_cong_ops __read_mostly = {
+	.flags		= TCP_CONG_NON_RESTRICTED | TCP_CONG_WANTS_CE_EVENTS,
+	.name		= "bbr2",
+	.owner		= THIS_MODULE,
+	.init		= bbr2_init,
+	.cong_control	= bbr2_main,
+	.sndbuf_expand	= bbr_sndbuf_expand,
+	.skb_marked_lost = bbr2_skb_marked_lost,
+	.undo_cwnd	= bbr2_undo_cwnd,
+	.cwnd_event	= bbr_cwnd_event,
+	.ssthresh	= bbr2_ssthresh,
+	.tso_segs	= bbr_tso_segs,
+	.get_info	= bbr2_get_info,
+	.set_state	= bbr2_set_state,
+};
+
+static int __init bbr_register(void)
+{
+	BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);
+	return tcp_register_congestion_control(&tcp_bbr2_cong_ops);
+}
+
+static void __exit bbr_unregister(void)
+{
+	tcp_unregister_congestion_control(&tcp_bbr2_cong_ops);
+}
+
+module_init(bbr_register);
+module_exit(bbr_unregister);
+
+MODULE_AUTHOR("Van Jacobson <vanj@google.com>");
+MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>");
+MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>");
+MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>");
+MODULE_AUTHOR("Priyaranjan Jha <priyarjha@google.com>");
+MODULE_AUTHOR("Yousuk Seung <ysseung@google.com>");
+MODULE_AUTHOR("Kevin Yang <yyd@google.com>");
+MODULE_AUTHOR("Arjun Roy <arjunroy@google.com>");
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index d3cae40749e8..0f268f2ff2e9 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -189,6 +189,7 @@ void tcp_init_congestion_control(struct sock *sk)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
 	tcp_sk(sk)->prior_ssthresh = 0;
+	tcp_sk(sk)->fast_ack_mode = 0;
 	if (icsk->icsk_ca_ops->init)
 		icsk->icsk_ca_ops->init(sk);
 	if (tcp_ca_needs_ecn(sk))
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0640453fce54..8a455eb0c552 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -349,7 +349,7 @@ static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 			tcp_enter_quickack_mode(sk, 2);
 		break;
 	case INET_ECN_CE:
-		if (tcp_ca_needs_ecn(sk))
+		if (tcp_ca_wants_ce_events(sk))
 			tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
 
 		if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
@@ -360,7 +360,7 @@ static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
 		tp->ecn_flags |= TCP_ECN_SEEN;
 		break;
 	default:
-		if (tcp_ca_needs_ecn(sk))
+		if (tcp_ca_wants_ce_events(sk))
 			tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
 		tp->ecn_flags |= TCP_ECN_SEEN;
 		break;
@@ -1079,7 +1079,12 @@ static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
  */
 static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb)
 {
+	struct sock *sk = (struct sock *)tp;
+	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
+
 	tp->lost += tcp_skb_pcount(skb);
+	if (ca_ops->skb_marked_lost)
+		ca_ops->skb_marked_lost(sk, skb);
 }
 
 void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
@@ -1460,6 +1465,17 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
 	WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount);
 	tcp_skb_pcount_add(skb, -pcount);
 
+	/* Adjust tx.in_flight as pcount is shifted from skb to prev. */
+	if (WARN_ONCE(TCP_SKB_CB(skb)->tx.in_flight < pcount,
+		      "prev in_flight: %u skb in_flight: %u pcount: %u",
+		      TCP_SKB_CB(prev)->tx.in_flight,
+		      TCP_SKB_CB(skb)->tx.in_flight,
+		      pcount))
+		TCP_SKB_CB(skb)->tx.in_flight = 0;
+	else
+		TCP_SKB_CB(skb)->tx.in_flight -= pcount;
+	TCP_SKB_CB(prev)->tx.in_flight += pcount;
+
 	/* When we're adding to gso_segs == 1, gso_size will be zero,
 	 * in theory this shouldn't be necessary but as long as DSACK
 	 * code can come after this skb later on it's better to keep
@@ -3812,6 +3828,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 
 	prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
 	rs.prior_in_flight = tcp_packets_in_flight(tp);
+	tcp_rate_check_app_limited(sk);
 
 	/* ts_recent update must be made after we are sure that the packet
 	 * is in window.
@@ -3910,6 +3927,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	delivered = tcp_newly_delivered(sk, delivered, flag);
 	lost = tp->lost - lost;			/* freshly marked lost */
 	rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
+	rs.is_ece = !!(flag & FLAG_ECE);
 	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
 	tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
 	tcp_xmit_recovery(sk, rexmit);
@@ -5509,13 +5527,14 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
 
 	    /* More than one full frame received... */
 	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
+	     (tp->fast_ack_mode == 1 ||
 	     /* ... and right edge of window advances far enough.
 	      * (tcp_recvmsg() will send ACK otherwise).
 	      * If application uses SO_RCVLOWAT, we want send ack now if
 	      * we have not received enough bytes to satisfy the condition.
 	      */
-	    (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
-	     __tcp_select_window(sk) >= tp->rcv_wnd)) ||
+	      (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
+	       __tcp_select_window(sk) >= tp->rcv_wnd))) ||
 	    /* We ACK each frame or... */
 	    tcp_in_quickack_mode(sk) ||
 	    /* Protocol state mandates a one-time immediate ACK */
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c69f4d966024..a9ceec2702b2 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -375,7 +375,8 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
 				th->cwr = 1;
 				skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
 			}
-		} else if (!tcp_ca_needs_ecn(sk)) {
+		} else if (!(tp->ecn_flags & TCP_ECN_ECT_PERMANENT) &&
+			!tcp_ca_needs_ecn(sk)) {
 			/* ACK or retransmitted segment: clear ECT|CE */
 			INET_ECN_dontxmit(sk);
 		}
@@ -1533,7 +1533,7 @@
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *buff;
-	int old_factor;
+	int old_factor, inflight_prev;
 	long limit;
 	int nlen;
 	u8 flags;
@@ -1610,6 +1611,15 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
 
 		if (diff)
 			tcp_adjust_pcount(sk, skb, diff);
+
+		/* Set buff tx.in_flight as if buff were sent by itself. */
+		inflight_prev = TCP_SKB_CB(skb)->tx.in_flight - old_factor;
+		if (WARN_ONCE(inflight_prev < 0,
+			      "inconsistent: tx.in_flight: %u old_factor: %d",
+			      TCP_SKB_CB(skb)->tx.in_flight, old_factor))
+			inflight_prev = 0;
+		TCP_SKB_CB(buff)->tx.in_flight = inflight_prev +
+						 tcp_skb_pcount(buff);
 	}
 
 	/* Link BUFF into the send queue. */
@@ -1993,13 +2003,12 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
 {
 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
-	u32 min_tso, tso_segs;
-
-	min_tso = ca_ops->min_tso_segs ?
-			ca_ops->min_tso_segs(sk) :
-			READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
+	u32 tso_segs;
 
-	tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
+	tso_segs = ca_ops->tso_segs ?
+		ca_ops->tso_segs(sk, mss_now) :
+		tcp_tso_autosize(sk, mss_now,
+				 READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs));
 	return min_t(u32, tso_segs, sk->sk_gso_max_segs);
 }
 
@@ -2635,6 +2644,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 			skb_set_delivery_time(skb, tp->tcp_wstamp_ns, true);
 			list_move_tail(&skb->tcp_tsorted_anchor, &tp->tsorted_sent_queue);
 			tcp_init_tso_segs(skb, mss_now);
+			tcp_set_tx_in_flight(sk, skb);
 			goto repair; /* Skip network transmission */
 		}
 
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index a8f6d9d06f2e..a8b4c9504570 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -34,6 +34,24 @@
  * ready to send in the write queue.
  */
 
+void tcp_set_tx_in_flight(struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 in_flight;
+
+	/* Check, sanitize, and record packets in flight after skb was sent. */
+	in_flight = tcp_packets_in_flight(tp) + tcp_skb_pcount(skb);
+	if (WARN_ONCE(in_flight > TCPCB_IN_FLIGHT_MAX,
+		      "insane in_flight %u cc %s mss %u "
+		      "cwnd %u pif %u %u %u %u\n",
+		      in_flight, inet_csk(sk)->icsk_ca_ops->name,
+		      tp->mss_cache, tp->snd_cwnd,
+		      tp->packets_out, tp->retrans_out,
+		      tp->sacked_out, tp->lost_out))
+		in_flight = TCPCB_IN_FLIGHT_MAX;
+	TCP_SKB_CB(skb)->tx.in_flight = in_flight;
+}
+
 /* Snapshot the current delivery information in the skb, to generate
  * a rate sample later when the skb is (s)acked in tcp_rate_skb_delivered().
  */
@@ -66,7 +84,9 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
 	TCP_SKB_CB(skb)->tx.delivered_mstamp	= tp->delivered_mstamp;
 	TCP_SKB_CB(skb)->tx.delivered		= tp->delivered;
 	TCP_SKB_CB(skb)->tx.delivered_ce	= tp->delivered_ce;
+	TCP_SKB_CB(skb)->tx.lost		= tp->lost;
 	TCP_SKB_CB(skb)->tx.is_app_limited	= tp->app_limited ? 1 : 0;
+	tcp_set_tx_in_flight(sk, skb);
 }
 
 /* When an skb is sacked or acked, we fill in the rate sample with the (prior)
@@ -91,18 +111,21 @@ void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 	if (!rs->prior_delivered ||
 	    tcp_skb_sent_after(tx_tstamp, tp->first_tx_mstamp,
 			       scb->end_seq, rs->last_end_seq)) {
+		rs->prior_lost	     = scb->tx.lost;
 		rs->prior_delivered_ce  = scb->tx.delivered_ce;
 		rs->prior_delivered  = scb->tx.delivered;
 		rs->prior_mstamp     = scb->tx.delivered_mstamp;
 		rs->is_app_limited   = scb->tx.is_app_limited;
 		rs->is_retrans	     = scb->sacked & TCPCB_RETRANS;
 		rs->last_end_seq     = scb->end_seq;
+		rs->tx_in_flight     = scb->tx.in_flight;
 
 		/* Record send time of most recently ACKed packet: */
 		tp->first_tx_mstamp  = tx_tstamp;
 		/* Find the duration of the "send phase" of this window: */
-		rs->interval_us = tcp_stamp_us_delta(tp->first_tx_mstamp,
-						     scb->tx.first_tx_mstamp);
+		rs->interval_us      = tcp_stamp32_us_delta(
+						tp->first_tx_mstamp,
+						scb->tx.first_tx_mstamp);
 
 	}
 	/* Mark off the skb delivered once it's sacked to avoid being
@@ -144,6 +167,7 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
 		return;
 	}
 	rs->delivered   = tp->delivered - rs->prior_delivered;
+	rs->lost        = tp->lost - rs->prior_lost;
 
 	rs->delivered_ce = tp->delivered_ce - rs->prior_delivered_ce;
 	/* delivered_ce occupies less than 32 bits in the skb control block */
@@ -155,7 +179,7 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
 	 * longer phase.
 	 */
 	snd_us = rs->interval_us;				/* send phase */
-	ack_us = tcp_stamp_us_delta(tp->tcp_mstamp,
+	ack_us = tcp_stamp32_us_delta(tp->tcp_mstamp,
 				    rs->prior_mstamp); /* ack phase */
 	rs->interval_us = max(snd_us, ack_us);
 
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index cb79127f45c3..70e4de876a7f 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -605,6 +605,7 @@ void tcp_write_timer_handler(struct sock *sk)
 		return;
 	}
 
+	tcp_rate_check_app_limited(sk);
 	tcp_mstamp_refresh(tcp_sk(sk));
 	event = icsk->icsk_pending;
 
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -287,7 +287,7 @@
 		icsk->icsk_ack.quick = quickacks;
 }
 
+void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
-static void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
@@ -295,6 +299,7 @@
 	inet_csk_exit_pingpong_mode(sk);
 	icsk->icsk_ack.ato = TCP_ATO_MIN;
 }
+EXPORT_SYMBOL(tcp_enter_quickack_mode);
 
 /* Send ACKs quickly, if "quick" count is not exhausted
  * and the session is not interactive.
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -350,6 +350,7 @@
 struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, gfp_t gfp,
 				     bool force_schedule);
 
+void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks);
 static inline void tcp_dec_quickack_mode(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);