convert_official_linux-4.14.x_src_to_bbrplus.patch

diff -ruaN a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
--- a/drivers/nvme/host/core.c	2022-10-26 19:17:14.000000000 +0800
+++ b/drivers/nvme/host/core.c	2022-11-12 21:11:01.891319293 +0800
@@ -34,13 +34,13 @@
 
 #define NVME_MINORS		(1U << MINORBITS)
 
-unsigned char admin_timeout = 60;
-module_param(admin_timeout, byte, 0644);
+unsigned int admin_timeout = 60;
+module_param(admin_timeout, uint, 0644);
 MODULE_PARM_DESC(admin_timeout, "timeout in seconds for admin commands");
 EXPORT_SYMBOL_GPL(admin_timeout);
 
-unsigned char nvme_io_timeout = 30;
-module_param_named(io_timeout, nvme_io_timeout, byte, 0644);
+unsigned int nvme_io_timeout = 30;
+module_param_named(io_timeout, nvme_io_timeout, uint, 0644);
 MODULE_PARM_DESC(io_timeout, "timeout in seconds for I/O");
 EXPORT_SYMBOL_GPL(nvme_io_timeout);
 
diff -ruaN a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
--- a/drivers/nvme/host/nvme.h	2022-10-26 19:17:14.000000000 +0800
+++ b/drivers/nvme/host/nvme.h	2022-11-12 21:11:01.891319293 +0800
@@ -21,10 +21,10 @@
 #include <linux/lightnvm.h>
 #include <linux/sed-opal.h>
 
-extern unsigned char nvme_io_timeout;
+extern unsigned int nvme_io_timeout;
 #define NVME_IO_TIMEOUT	(nvme_io_timeout * HZ)
 
-extern unsigned char admin_timeout;
+extern unsigned int admin_timeout;
 #define ADMIN_TIMEOUT	(admin_timeout * HZ)
 
 #define NVME_DEFAULT_KATO	5
diff -ruaN a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
--- a/include/net/inet_connection_sock.h	2022-10-26 19:17:14.000000000 +0800
+++ b/include/net/inet_connection_sock.h	2022-11-12 21:11:01.891319293 +0800
@@ -136,8 +136,8 @@
 	} icsk_mtup;
 	u32			  icsk_user_timeout;
 
-	u64			  icsk_ca_priv[88 / sizeof(u64)];
-#define ICSK_CA_PRIV_SIZE      (11 * sizeof(u64))
+	u64			  icsk_ca_priv[112 / sizeof(u64)];
+#define ICSK_CA_PRIV_SIZE      (14 * sizeof(u64))
 };
 
 #define ICSK_TIME_RETRANS	1	/* Retransmit timer */
diff -ruaN a/net/ipv4/Kconfig b/net/ipv4/Kconfig
--- a/net/ipv4/Kconfig	2022-10-26 19:17:14.000000000 +0800
+++ b/net/ipv4/Kconfig	2022-11-12 21:11:01.891319293 +0800
@@ -503,7 +503,7 @@
 
 config TCP_CONG_CUBIC
 	tristate "CUBIC TCP"
-	default y
+	default m
 	---help---
 	This is version 2.0 of BIC-TCP which uses a cubic growth function
 	among other techniques.
@@ -686,9 +686,18 @@
 	bufferbloat, policers, or AQM schemes that do not provide a delay
 	signal. It requires the fq ("Fair Queue") pacing packet scheduler.
 
+config TCP_CONG_BBRPLUS
+        tristate "BBRPLUS TCP"
+        default y
+        ---help---
+
+        BBRplus is an enhanced version of BBR (Bottleneck Bandwidth and RTT).
+        Originally introduced by dog250 & cx9208.
+        Same as BBR, requires the fq ("Fair Queue") pacing packet scheduler.
+
 choice
 	prompt "Default TCP congestion control"
-	default DEFAULT_CUBIC
+	default DEFAULT_BBRPLUS
 	help
 	  Select the TCP congestion control that will be used by default
 	  for all connections.
@@ -696,8 +705,8 @@
 	config DEFAULT_BIC
 		bool "Bic" if TCP_CONG_BIC=y
 
-	config DEFAULT_CUBIC
-		bool "Cubic" if TCP_CONG_CUBIC=y
+        config DEFAULT_CUBIC
+                bool "Cubic" if TCP_CONG_CUBIC=y
 
 	config DEFAULT_HTCP
 		bool "Htcp" if TCP_CONG_HTCP=y
@@ -723,6 +732,9 @@
 	config DEFAULT_BBR
 		bool "BBR" if TCP_CONG_BBR=y
 
+        config DEFAULT_BBRPLUS
+                bool "BBRPLUS" if TCP_CONG_BBRPLUS=y
+
 	config DEFAULT_RENO
 		bool "Reno"
 endchoice
@@ -737,7 +749,7 @@
 config DEFAULT_TCP_CONG
 	string
 	default "bic" if DEFAULT_BIC
-	default "cubic" if DEFAULT_CUBIC
+        default "cubic" if DEFAULT_CUBIC
 	default "htcp" if DEFAULT_HTCP
 	default "hybla" if DEFAULT_HYBLA
 	default "vegas" if DEFAULT_VEGAS
@@ -747,7 +759,8 @@
 	default "dctcp" if DEFAULT_DCTCP
 	default "cdg" if DEFAULT_CDG
 	default "bbr" if DEFAULT_BBR
-	default "cubic"
+        default "bbrplus" if DEFAULT_BBRPLUS
+	default "bbrplus"
 
 config TCP_MD5SIG
 	bool "TCP: MD5 Signature Option support (RFC2385)"
diff -ruaN a/net/ipv4/Makefile b/net/ipv4/Makefile
--- a/net/ipv4/Makefile	2022-10-26 19:17:14.000000000 +0800
+++ b/net/ipv4/Makefile	2022-11-12 21:11:01.891319293 +0800
@@ -45,6 +45,7 @@
 obj-$(CONFIG_INET_RAW_DIAG) += raw_diag.o
 obj-$(CONFIG_NET_TCPPROBE) += tcp_probe.o
 obj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o
+obj-$(CONFIG_TCP_CONG_BBRPLUS) += tcp_bbrplus.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 -ruaN a/net/ipv4/tcp_bbrplus.c b/net/ipv4/tcp_bbrplus.c
--- a/net/ipv4/tcp_bbrplus.c	1970-01-01 08:00:00.000000000 +0800
+++ b/net/ipv4/tcp_bbrplus.c	2022-11-12 21:11:01.891319293 +0800
@@ -0,0 +1,1187 @@
+/* Bottleneck Bandwidth and RTT (BBR) congestion control
+ *
+ * BBR congestion control computes the sending rate based on the delivery
+ * rate (throughput) estimated from ACKs. In a nutshell:
+ *
+ *   On each ACK, update our model of the network path:
+ *      bottleneck_bandwidth = windowed_max(delivered / elapsed, 10 round trips)
+ *      min_rtt = windowed_min(rtt, 10 seconds)
+ *   pacing_rate = pacing_gain * bottleneck_bandwidth
+ *   cwnd = max(cwnd_gain * bottleneck_bandwidth * min_rtt, 4)
+ *
+ * The core algorithm does not react directly to packet losses or delays,
+ * although BBR may adjust the size of next send per ACK when loss is
+ * observed, or adjust the sending rate if it estimates there is a
+ * traffic policer, in order to keep the drop rate reasonable.
+ *
+ * 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 <linux/win_minmax.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)
+
+/* 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 */
+};
+
+/* 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 */
+    struct minmax bw;   /* Max recent delivery rate in pkts/uS << 24 */
+    u32 rtt_cnt;        /* count of packet-timed rounds elapsed */
+    u32     next_rtt_delivered; /* scb->tx.delivered at end of round */
+    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? */
+        restore_cwnd:1,      /* decided to revert cwnd to old value */
+        round_start:1,       /* start of packet-timed tx->ack round? */
+        cycle_len:4,         /* phases in this PROBE_BW gain cycle */
+        tso_segs_goal:7,     /* segments we want in each skb we send */
+        idle_restart:1,      /* restarting after idle? */
+        probe_rtt_round_done:1,  /* a BBR_PROBE_RTT round at 4 pkts? */
+        unused:8,
+        lt_is_sampling:1,    /* taking long-term ("LT") samples now? */
+        lt_rtt_cnt:7,        /* round trips in long-term interval */
+        lt_use_bw:1;         /* use lt_bw as our bw estimate? */
+    u32 lt_bw;           /* LT est delivery rate in pkts/uS << 24 */
+    u32 lt_last_delivered;   /* LT intvl start: tp->delivered */
+    u32 lt_last_stamp;       /* LT intvl start: tp->delivered_mstamp */
+    u32 lt_last_lost;        /* LT intvl start: tp->lost */
+    u32 pacing_gain:10, /* current gain for setting pacing rate */
+        cwnd_gain:10,   /* 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 */
+        cycle_idx:3,    /* current index in pacing_gain cycle array */
+        has_seen_rtt:1, /* have we seen an RTT sample yet? */
+        unused_b:5;
+    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 */
+        unused1:6;
+};
+
+#define CYCLE_LEN   8   /* number of phases in a pacing gain cycle */
+
+/* Window length of bw filter (in rounds): */
+static const int bbr_bw_rtts = CYCLE_LEN + 2;
+/* Window length of min_rtt filter (in sec): */
+static const u32 bbr_min_rtt_win_sec = 10;
+/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */
+static const u32 bbr_probe_rtt_mode_ms = 200;
+/* Skip TSO below the following bandwidth (bits/sec): */
+static const int bbr_min_tso_rate = 1200000;
+
+/* 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:
+ */
+static const int bbr_high_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:
+ */
+static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885;
+/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */
+static const int bbr_cwnd_gain  = BBR_UNIT * 2;
+
+enum bbr_pacing_gain_phase {
+    BBR_BW_PROBE_UP     = 0,
+    BBR_BW_PROBE_DOWN   = 1,
+    BBR_BW_PROBE_CRUISE = 2,
+};
+
+/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */
+static const 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... */
+};
+/* Randomize the starting gain cycling phase over N phases: */
+static const u32 bbr_cycle_rand = 7;
+
+/* 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:
+ */
+static const u32 bbr_cwnd_min_target = 4;
+
+/* 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: */
+static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4;
+/* But after 3 rounds w/o significant bw growth, estimate pipe is full: */
+static const u32 bbr_full_bw_cnt = 3;
+
+/* "long-term" ("LT") bandwidth estimator parameters... */
+/* The minimum number of rounds in an LT bw sampling interval: */
+static const u32 bbr_lt_intvl_min_rtts = 4;
+/* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */
+static const u32 bbr_lt_loss_thresh = 50;
+/* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */
+static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8;
+/* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */
+static const u32 bbr_lt_bw_diff = 4000 / 8;
+/* If we estimate we're policed, use lt_bw for this many round trips: */
+static const u32 bbr_lt_bw_max_rtts = 48;
+
+/* Gain factor for adding extra_acked to target cwnd: */
+static const int bbr_extra_acked_gain = BBR_UNIT;
+/* Window length of extra_acked window. Max allowed val is 31. */
+static const u32 bbr_extra_acked_win_rtts = 10;
+/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */
+static const u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20;
+/* Time period for clamping cwnd increment due to ack aggregation */
+static const u32 bbr_extra_acked_max_us = 100 * 1000;
+
+/* Each cycle, try to hold sub-unity gain until inflight <= BDP. */
+static const bool bbr_drain_to_target = true;   /* default: enabled */
+
+static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
+                             const struct sk_buff *skb,
+                             unsigned int cur_mss)
+{
+        u32 end_seq = TCP_SKB_CB(skb)->end_seq;
+
+        if (skb->len > cur_mss)
+                end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
+
+        return !after(end_seq, tcp_wnd_end(tp));
+}
+
+/* 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;
+}
+
+static void bbr_set_cycle_idx(struct sock *sk, int cycle_idx)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+    bbr->cycle_idx = cycle_idx;
+    bbr->pacing_gain = bbr->lt_use_bw ?
+                            BBR_UNIT : bbr_pacing_gain[bbr->cycle_idx];
+}
+
+u32 bbr_max_bw(const struct sock *sk);
+u32 bbr_inflight(struct sock *sk, u32 bw, int gain);
+u32 bbr_max_bw(const struct sock *sk);
+
+static void bbr_drain_to_target_cycling(struct sock *sk,
+                                                    const struct rate_sample *rs)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    u32 elapsed_us =
+                tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp);
+    u32 inflight, bw;
+    if (bbr->mode != BBR_PROBE_BW)
+        return;
+
+    /* Always need to probe for bw before we forget good bw estimate. */
+    if (elapsed_us > bbr->cycle_len * bbr->min_rtt_us) {
+        /* Start a new PROBE_BW probing cycle of [2 to 8] x min_rtt. */
+        bbr->cycle_mstamp = tp->delivered_mstamp;
+        bbr->cycle_len = CYCLE_LEN - prandom_u32_max(bbr_cycle_rand);
+        bbr_set_cycle_idx(sk, BBR_BW_PROBE_UP);  /* probe bandwidth */
+        return;
+    }
+    /* The pacing_gain of 1.0 paces at the estimated bw to try to fully
+     * use the pipe without increasing the queue.
+     */
+    if (bbr->pacing_gain == BBR_UNIT)
+        return;
+    inflight = rs->prior_in_flight;  /* what was in-flight before ACK? */
+    bw = bbr_max_bw(sk);
+    /* A pacing_gain < 1.0 tries to drain extra queue we added if bw
+     * probing didn't find more bw. If inflight falls to match BDP then we
+     * estimate queue is drained; persisting would underutilize the pipe.
+     */
+    if (bbr->pacing_gain < BBR_UNIT) {
+        if (inflight <= bbr_inflight(sk, bw, BBR_UNIT))
+            bbr_set_cycle_idx(sk, BBR_BW_PROBE_CRUISE); /* cruise */
+        return;
+    }
+    /* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at
+     * least pacing_gain*BDP; this may take more than min_rtt if min_rtt is
+     * small (e.g. on a LAN). We do not persist if packets are lost, since
+     * a path with small buffers may not hold that much. Similarly we exit
+     * if we were prevented by app/recv-win from reaching the target.
+     */
+    if (elapsed_us > bbr->min_rtt_us &&
+            (inflight >= bbr_inflight(sk, bw, bbr->pacing_gain) ||
+            rs->losses ||         /* perhaps pacing_gain*BDP won't fit */
+            rs->is_app_limited || /* previously app-limited */
+            !tcp_send_head(sk) || /* currently app/rwin-limited */
+            !tcp_snd_wnd_test(tp, tcp_send_head(sk), tp->mss_cache))) {
+            bbr_set_cycle_idx(sk, BBR_BW_PROBE_DOWN);  /* drain queue */
+            return;
+    }
+}
+
+
+/* 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 the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */
+u32 bbr_max_bw(const struct sock *sk)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    return minmax_get(&bbr->bw);
+}
+
+/* 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 bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk);
+}
+
+/* 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)
+{
+    rate *= tcp_mss_to_mtu(sk, tcp_sk(sk)->mss_cache);
+    rate *= gain;
+    rate >>= BBR_SCALE;
+    rate *= USEC_PER_SEC;
+    return rate >> BW_SCALE;
+}
+
+/* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */
+static u32 bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)
+{
+    u64 rate = bw;
+
+    rate = bbr_rate_bytes_per_sec(sk, rate, gain);
+    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_high_gain);
+}
+
+/* Pace using current bw estimate and a gain factor. In order to help drive the
+ * network toward lower queues while maintaining high utilization and low
+ * latency, the average pacing rate aims to be slightly (~1%) lower than the
+ * estimated bandwidth. This is an important aspect of the design. In this
+ * implementation this slightly lower pacing rate is achieved implicitly by not
+ * including link-layer headers in the packet size used for the pacing rate.
+ */
+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);
+    u32 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;
+}
+
+/* Return count of segments we want in the skbs we send, or 0 for default. */
+static u32 bbr_tso_segs_goal(struct sock *sk)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    return bbr->tso_segs_goal;
+}
+
+static void bbr_set_tso_segs_goal(struct sock *sk)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    u32 min_segs;
+
+    min_segs = sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
+    bbr->tso_segs_goal = min(tcp_tso_autosize(sk, tp->mss_cache, min_segs),
+                 0x7FU);
+}
+
+/* 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);
+    }
+}
+
+/* Find target cwnd. Right-size the cwnd based on min RTT and the
+ * estimated bottleneck bandwidth:
+ *
+ * cwnd = bw * min_rtt * gain = BDP * 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.
+ *
+ * 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_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: TCP_INIT_CWND.
+     */
+    if (unlikely(bbr->min_rtt_us == ~0U))   /* no valid RTT samples yet? */
+        return TCP_INIT_CWND;  /* be safe: cap at default initial cwnd*/
+
+    w = (u64)bw * bbr->min_rtt_us;
+
+    /* Apply a gain to the given value, then remove the BW_SCALE shift. */
+    bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT;
+
+    return bdp;
+}
+
+static u32 bbr_quantization_budget(struct sock *sk, u32 cwnd, int gain)
+{
+
+    /* Allow enough full-sized skbs in flight to utilize end systems. */
+    cwnd += 3 * bbr_tso_segs_goal(sk);
+
+    return cwnd;
+}
+
+/* Find inflight based on min RTT and the estimated bottleneck bandwidth. */
+u32 bbr_inflight(struct sock *sk, u32 bw, int gain)
+{   
+    u32 inflight;
+    inflight = bbr_bdp(sk, bw, gain);
+    inflight = bbr_quantization_budget(sk, inflight, gain);
+    return inflight;
+
+}
+
+/* Find the cwnd increment based on estimate of ack aggregation */
+static u32 bbr_ack_aggregation_cwnd(struct sock *sk)
+{
+    u32 max_aggr_cwnd, aggr_cwnd = 0;
+    if (bbr_extra_acked_gain && bbr_full_bw_reached(sk)) {
+        max_aggr_cwnd = ((u64)bbr_bw(sk) * bbr_extra_acked_max_us)
+            / BW_UNIT;
+        aggr_cwnd = (bbr_extra_acked_gain * bbr_extra_acked(sk))
+            >> BBR_SCALE;
+        aggr_cwnd = min(aggr_cwnd, max_aggr_cwnd);
+    }
+    return aggr_cwnd;
+}
+
+
+/* An optimization in BBR to reduce losses: On the first round of recovery, we
+ * follow the packet conservation principle: send P packets per P packets acked.
+ * After that, we slow-start and send at most 2*P packets per P packets acked.
+ * After recovery finishes, or upon undo, we restore the cwnd we had when
+ * recovery started (capped by the target cwnd based on estimated BDP).
+ *
+ * TODO(ycheng/ncardwell): implement a rate-based approach.
+ */
+static bool bbr_set_cwnd_to_recover_or_restore(
+    struct sock *sk, const struct rate_sample *rs, u32 acked, u32 *new_cwnd)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state;
+    u32 cwnd = tp->snd_cwnd;
+
+    /* An ACK for P pkts should release at most 2*P packets. We do this
+     * in two steps. First, here we deduct the number of lost packets.
+     * Then, in bbr_set_cwnd() we slow start up toward the target cwnd.
+     */
+    if (rs->losses > 0)
+        cwnd = max_t(s32, cwnd - rs->losses, 1);
+
+    if (state == TCP_CA_Recovery && prev_state != TCP_CA_Recovery) {
+        /* Starting 1st round of Recovery, so do packet conservation. */
+        bbr->packet_conservation = 1;
+        bbr->next_rtt_delivered = tp->delivered;  /* start round now */
+        /* Cut unused cwnd from app behavior, TSQ, or TSO deferral: */
+        cwnd = tcp_packets_in_flight(tp) + acked;
+    } else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) {
+        /* Exiting loss recovery; restore cwnd saved before recovery. */
+        bbr->restore_cwnd = 1;
+        bbr->packet_conservation = 0;
+    }
+    bbr->prev_ca_state = state;
+
+    if (bbr->restore_cwnd) {
+        /* Restore cwnd after exiting loss recovery or PROBE_RTT. */
+        cwnd = max(cwnd, bbr->prior_cwnd);
+        bbr->restore_cwnd = 0;
+    }
+
+    if (bbr->packet_conservation) {
+        *new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked);
+        return true;    /* yes, using packet conservation */
+    }
+    *new_cwnd = cwnd;
+    return false;
+}
+
+/* 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)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    u32 cwnd = 0, target_cwnd = 0;
+
+    if (!acked)
+        return;
+
+    if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd))
+        goto done;
+
+    /* If we're below target cwnd, slow start cwnd toward target cwnd. */
+    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, gain);
+    if (bbr_full_bw_reached(sk))  /* only cut cwnd if we filled the pipe */
+        cwnd = min(cwnd + acked, target_cwnd);
+    else if (cwnd < target_cwnd || tp->delivered < TCP_INIT_CWND)
+        cwnd = cwnd + acked;
+    cwnd = max(cwnd, bbr_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(tp->snd_cwnd, bbr_cwnd_min_target);
+}
+
+/* End cycle phase if it's time and/or we hit the phase's in-flight target. */
+static bool bbr_is_next_cycle_phase(struct sock *sk,
+                    const struct rate_sample *rs)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    bool is_full_length =
+        tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp) >
+        bbr->min_rtt_us;
+    u32 inflight, bw;
+
+    /* The pacing_gain of 1.0 paces at the estimated bw to try to fully
+     * use the pipe without increasing the queue.
+     */
+    if (bbr->pacing_gain == BBR_UNIT)
+        return is_full_length;      /* just use wall clock time */
+
+    inflight = rs->prior_in_flight;  /* what was in-flight before ACK? */
+    bw = bbr_max_bw(sk);
+
+    /* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at
+     * least pacing_gain*BDP; this may take more than min_rtt if min_rtt is
+     * small (e.g. on a LAN). We do not persist if packets are lost, since
+     * a path with small buffers may not hold that much.
+     */
+    if (bbr->pacing_gain > BBR_UNIT)
+        return is_full_length &&
+            (rs->losses ||  /* perhaps pacing_gain*BDP won't fit */
+             inflight >= bbr_inflight(sk, bw, bbr->pacing_gain));
+
+    /* A pacing_gain < 1.0 tries to drain extra queue we added if bw
+     * probing didn't find more bw. If inflight falls to match BDP then we
+     * estimate queue is drained; persisting would underutilize the pipe.
+     */
+    return is_full_length ||
+        inflight <= bbr_inflight(sk, bw, BBR_UNIT);
+}
+
+static void bbr_advance_cycle_phase(struct sock *sk)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+
+
+    bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1);
+    bbr->cycle_mstamp = tp->delivered_mstamp;
+    bbr->pacing_gain = bbr->lt_use_bw ? BBR_UNIT :
+    			    					    					    bbr_pacing_gain[bbr->cycle_idx];
+}
+
+/* Gain cycling: cycle pacing gain to converge to fair share of available bw. */
+static void bbr_update_cycle_phase(struct sock *sk,
+                   const struct rate_sample *rs)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    if (bbr_drain_to_target) {
+        bbr_drain_to_target_cycling(sk, rs);
+        return;
+    }
+
+    if (bbr->mode == BBR_PROBE_BW && bbr_is_next_cycle_phase(sk, rs))
+        bbr_advance_cycle_phase(sk);
+}
+
+static void bbr_reset_startup_mode(struct sock *sk)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    bbr->mode = BBR_STARTUP;
+    bbr->pacing_gain = bbr_high_gain;
+    bbr->cwnd_gain   = bbr_high_gain;
+}
+
+static void bbr_reset_probe_bw_mode(struct sock *sk)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    bbr->mode = BBR_PROBE_BW;
+    bbr->pacing_gain = BBR_UNIT;
+    bbr->cwnd_gain = bbr_cwnd_gain;
+    bbr->cycle_idx = CYCLE_LEN - 1 - prandom_u32_max(bbr_cycle_rand);
+    bbr_advance_cycle_phase(sk);    /* flip to next phase of gain cycle */
+}
+
+static void bbr_reset_mode(struct sock *sk)
+{
+    if (!bbr_full_bw_reached(sk))
+        bbr_reset_startup_mode(sk);
+    else
+        bbr_reset_probe_bw_mode(sk);
+}
+
+/* Start a new long-term sampling interval. */
+static void bbr_reset_lt_bw_sampling_interval(struct sock *sk)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    bbr->lt_last_stamp = div_u64(tp->delivered_mstamp, USEC_PER_MSEC);
+    bbr->lt_last_delivered = tp->delivered;
+    bbr->lt_last_lost = tp->lost;
+    bbr->lt_rtt_cnt = 0;
+}
+
+/* Completely reset long-term bandwidth sampling. */
+static void bbr_reset_lt_bw_sampling(struct sock *sk)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    bbr->lt_bw = 0;
+    bbr->lt_use_bw = 0;
+    bbr->lt_is_sampling = false;
+    bbr_reset_lt_bw_sampling_interval(sk);
+}
+
+/* Long-term bw sampling interval is done. Estimate whether we're policed. */
+static void bbr_lt_bw_interval_done(struct sock *sk, u32 bw)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+    u32 diff;
+
+    if (bbr->lt_bw) {  /* do we have bw from a previous interval? */
+        /* Is new bw close to the lt_bw from the previous interval? */
+        diff = abs(bw - bbr->lt_bw);
+        if ((diff * BBR_UNIT <= bbr_lt_bw_ratio * bbr->lt_bw) ||
+            (bbr_rate_bytes_per_sec(sk, diff, BBR_UNIT) <=
+             bbr_lt_bw_diff)) {
+            /* All criteria are met; estimate we're policed. */
+            bbr->lt_bw = (bw + bbr->lt_bw) >> 1;  /* avg 2 intvls */
+            bbr->lt_use_bw = 1;
+            bbr->pacing_gain = BBR_UNIT;  /* try to avoid drops */
+            bbr->lt_rtt_cnt = 0;
+            return;
+        }
+    }
+    bbr->lt_bw = bw;
+    bbr_reset_lt_bw_sampling_interval(sk);
+}
+
+/* Token-bucket traffic policers are common (see "An Internet-Wide Analysis of
+ * Traffic Policing", SIGCOMM 2016). BBR detects token-bucket policers and
+ * explicitly models their policed rate, to reduce unnecessary losses. We
+ * estimate that we're policed if we see 2 consecutive sampling intervals with
+ * consistent throughput and high packet loss. If we think we're being policed,
+ * set lt_bw to the "long-term" average delivery rate from those 2 intervals.
+ */
+static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    u32 lost, delivered;
+    u64 bw;
+    u32 t;
+
+    if (bbr->lt_use_bw) {   /* already using long-term rate, lt_bw? */
+        if (bbr->mode == BBR_PROBE_BW && bbr->round_start &&
+            ++bbr->lt_rtt_cnt >= bbr_lt_bw_max_rtts) {
+            bbr_reset_lt_bw_sampling(sk);    /* stop using lt_bw */
+            bbr_reset_probe_bw_mode(sk);  /* restart gain cycling */
+        }
+        return;
+    }
+
+    /* Wait for the first loss before sampling, to let the policer exhaust
+     * its tokens and estimate the steady-state rate allowed by the policer.
+     * Starting samples earlier includes bursts that over-estimate the bw.
+     */
+    if (!bbr->lt_is_sampling) {
+        if (!rs->losses)
+            return;
+        bbr_reset_lt_bw_sampling_interval(sk);
+        bbr->lt_is_sampling = true;
+    }
+
+    /* To avoid underestimates, reset sampling if we run out of data. */
+    if (rs->is_app_limited) {
+        bbr_reset_lt_bw_sampling(sk);
+        return;
+    }
+
+    if (bbr->round_start)
+        bbr->lt_rtt_cnt++;  /* count round trips in this interval */
+    if (bbr->lt_rtt_cnt < bbr_lt_intvl_min_rtts)
+        return;     /* sampling interval needs to be longer */
+    if (bbr->lt_rtt_cnt > 4 * bbr_lt_intvl_min_rtts) {
+        bbr_reset_lt_bw_sampling(sk);  /* interval is too long */
+        return;
+    }
+
+    /* End sampling interval when a packet is lost, so we estimate the
+     * policer tokens were exhausted. Stopping the sampling before the
+     * tokens are exhausted under-estimates the policed rate.
+     */
+    if (!rs->losses)
+        return;
+
+    /* Calculate packets lost and delivered in sampling interval. */
+    lost = tp->lost - bbr->lt_last_lost;
+    delivered = tp->delivered - bbr->lt_last_delivered;
+    /* Is loss rate (lost/delivered) >= lt_loss_thresh? If not, wait. */
+    if (!delivered || (lost << BBR_SCALE) < bbr_lt_loss_thresh * delivered)
+        return;
+
+    /* Find average delivery rate in this sampling interval. */
+    t = div_u64(tp->delivered_mstamp, USEC_PER_MSEC) - bbr->lt_last_stamp;
+    if ((s32)t < 1)
+        return;     /* interval is less than one ms, so wait */
+    /* Check if can multiply without overflow */
+    if (t >= ~0U / USEC_PER_MSEC) {
+        bbr_reset_lt_bw_sampling(sk);  /* interval too long; reset */
+        return;
+    }
+    t *= USEC_PER_MSEC;
+    bw = (u64)delivered * BW_UNIT;
+    do_div(bw, t);
+    bbr_lt_bw_interval_done(sk, bw);
+}
+
+/* Estimate the bandwidth based on how fast packets are delivered */
+static void bbr_update_bw(struct sock *sk, const struct rate_sample *rs)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+    u64 bw;
+
+    bbr->round_start = 0;
+    if (rs->delivered < 0 || rs->interval_us <= 0)
+        return; /* Not a valid observation */
+
+    /* See if we've reached the next RTT */
+    if (!before(rs->prior_delivered, bbr->next_rtt_delivered)) {
+        bbr->next_rtt_delivered = tp->delivered;
+        bbr->rtt_cnt++;
+        bbr->round_start = 1;
+        bbr->packet_conservation = 0;
+    }
+
+    bbr_lt_bw_sampling(sk, rs);
+
+    /* 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.
+     */
+    bw = div64_long((u64)rs->delivered * BW_UNIT, rs->interval_us);
+
+    /* If this sample is application-limited, it is likely to have a very
+     * low delivered count that represents application behavior rather than
+     * the available network rate. Such a sample could drag down estimated
+     * bw, causing needless slow-down. Thus, to continue to send at the
+     * last measured network rate, we filter out app-limited samples unless
+     * they describe the path bw at least as well as our bw model.
+     *
+     * So the goal during app-limited phase is to proceed with the best
+     * network rate no matter how long. We automatically leave this
+     * phase when app writes faster than the network can deliver :)
+     */
+    if (!rs->is_app_limited || bw >= bbr_max_bw(sk)) {
+        /* Incorporate new sample into our max bw filter. */
+        minmax_running_max(&bbr->bw, bbr_bw_rtts, bbr->rtt_cnt, bw);
+    }
+}
+
+/* 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_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_full_bw_cnt;
+}
+
+/* If pipe is probably full, drain the queue and then enter steady-state. */
+static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs)
+{
+    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 */
+        bbr->pacing_gain = bbr_drain_gain;  /* pace slow to drain */
+        bbr->cwnd_gain = bbr_high_gain; /* maintain cwnd */
+    }   /* fall through to check if in-flight is already small: */
+    if (bbr->mode == BBR_DRAIN &&
+        tcp_packets_in_flight(tcp_sk(sk)) <= bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT))
+        bbr_reset_probe_bw_mode(sk);  /* we estimate queue is drained */
+}
+
+
+/* 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 10-20 (packet timed) round
+ * trips.
+ */
+ 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);
+    if (!bbr_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->extra_acked_win_rtts >= bbr_extra_acked_win_rtts) {
+            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(0xFFFFFU,
+                                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;
+}
+
+/* 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 filter_expired;
+
+    /* Track min RTT seen in the min_rtt_win_sec filter window: */
+    filter_expired = after(tcp_jiffies32,
+                   bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ);
+    if (rs->rtt_us >= 0 &&
+        (rs->rtt_us < bbr->min_rtt_us || filter_expired)) {
+        bbr->min_rtt_us = rs->rtt_us;
+        bbr->min_rtt_stamp = tcp_jiffies32;
+    }
+
+    if (bbr_probe_rtt_mode_ms > 0 && filter_expired &&
+        !bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) {
+        bbr->mode = BBR_PROBE_RTT;  /* dip, drain queue */
+        bbr->pacing_gain = BBR_UNIT;
+        bbr->cwnd_gain = BBR_UNIT;
+        bbr_save_cwnd(sk);  /* note cwnd so we can restore it */
+        bbr->probe_rtt_done_stamp = 0;
+    }
+
+    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_cwnd_min_target) {
+            bbr->probe_rtt_done_stamp = tcp_jiffies32 +
+                msecs_to_jiffies(bbr_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 &&
+                after(tcp_jiffies32, bbr->probe_rtt_done_stamp)) {
+                bbr->min_rtt_stamp = tcp_jiffies32;
+                bbr->restore_cwnd = 1;  /* snap to prior_cwnd */
+                bbr_reset_mode(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_model(struct sock *sk, const struct rate_sample *rs)
+{
+    bbr_update_bw(sk, rs);
+    bbr_update_ack_aggregation(sk, rs);
+    bbr_update_cycle_phase(sk, rs);
+    bbr_check_full_bw_reached(sk, rs);
+    bbr_check_drain(sk, rs);
+    bbr_update_min_rtt(sk, rs);
+}
+
+static void bbr_main(struct sock *sk, const struct rate_sample *rs)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+    u32 bw;
+
+    bbr_update_model(sk, rs);
+
+    bw = bbr_bw(sk);
+    bbr_set_pacing_rate(sk, bw, bbr->pacing_gain);
+    bbr_set_tso_segs_goal(sk);
+    bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain);
+}
+
+static void bbr_init(struct sock *sk)
+{
+    struct tcp_sock *tp = tcp_sk(sk);
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    bbr->prior_cwnd = 0;
+    bbr->tso_segs_goal = 0;  /* default segs per skb until first ACK */
+    bbr->rtt_cnt = 0;
+    bbr->next_rtt_delivered = tp->delivered;
+    bbr->prev_ca_state = TCP_CA_Open;
+    bbr->packet_conservation = 0;
+
+    bbr->probe_rtt_done_stamp = 0;
+    bbr->probe_rtt_round_done = 0;
+    bbr->min_rtt_us = tcp_min_rtt(tp);
+    bbr->min_rtt_stamp = tcp_jiffies32;
+
+    minmax_reset(&bbr->bw, bbr->rtt_cnt, 0);  /* init max bw to 0 */
+
+    bbr->has_seen_rtt = 0;
+    bbr_init_pacing_rate_from_rtt(sk);
+
+    bbr->restore_cwnd = 0;
+    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->cycle_len = 0;
+    bbr_reset_lt_bw_sampling(sk);
+    bbr_reset_startup_mode(sk);
+    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;
+
+    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;
+}
+
+/* In theory BBR does not need to undo the cwnd since it does not
+ * always reduce cwnd on losses (see bbr_main()). Keep it for now.
+ */
+static u32 bbr_undo_cwnd(struct sock *sk)
+{
+	struct bbr *bbr = inet_csk_ca(sk);
+	
+	bbr->full_bw = 0;   /* spurious slow-down; reset full pipe detection */
+	bbr->full_bw_cnt = 0;
+	bbr_reset_lt_bw_sampling(sk);
+    return tcp_sk(sk)->snd_cwnd;
+}
+
+/* Entering loss recovery, so save cwnd for when we exit or undo recovery. */
+static u32 bbr_ssthresh(struct sock *sk)
+{
+    bbr_save_cwnd(sk);
+    return TCP_INFINITE_SSTHRESH;    /* BBR does not use ssthresh */
+}
+
+static size_t bbr_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 tcp_sock *tp = tcp_sk(sk);
+        struct bbr *bbr = inet_csk_ca(sk);
+        u64 bw = bbr_bw(sk);
+
+        bw = bw * tp->mss_cache * USEC_PER_SEC >> BW_SCALE;
+        memset(&info->bbr, 0, sizeof(info->bbr));
+        info->bbr.bbr_bw_lo     = (u32)bw;
+        info->bbr.bbr_bw_hi     = (u32)(bw >> 32);
+        info->bbr.bbr_min_rtt       = bbr->min_rtt_us;
+        info->bbr.bbr_pacing_gain   = bbr->pacing_gain;
+        info->bbr.bbr_cwnd_gain     = bbr->cwnd_gain;
+        *attr = INET_DIAG_BBRINFO;
+        return sizeof(info->bbr);
+    }
+    return 0;
+}
+
+static void bbr_set_state(struct sock *sk, u8 new_state)
+{
+    struct bbr *bbr = inet_csk_ca(sk);
+
+    if (new_state == TCP_CA_Loss) {
+        struct rate_sample rs = { .losses = 1 };
+
+        bbr->prev_ca_state = TCP_CA_Loss;
+        bbr->full_bw = 0;
+        bbr->round_start = 1;   /* treat RTO like end of a round */
+        bbr_lt_bw_sampling(sk, &rs);
+    }
+}
+
+static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
+    .flags      = TCP_CONG_NON_RESTRICTED,
+    .name       = "bbrplus",
+    .owner      = THIS_MODULE,
+    .init       = bbr_init,
+    .cong_control   = bbr_main,
+    .sndbuf_expand  = bbr_sndbuf_expand,
+    .undo_cwnd  = bbr_undo_cwnd,
+    .cwnd_event = bbr_cwnd_event,
+    .ssthresh   = bbr_ssthresh,
+    .tso_segs_goal  = bbr_tso_segs_goal,
+    .get_info   = bbr_get_info,
+    .set_state  = bbr_set_state,
+};
+
+static int __init bbr_register(void)
+{
+    BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);
+    return tcp_register_congestion_control(&tcp_bbr_cong_ops);
+}
+
+static void __exit bbr_unregister(void)
+{
+    tcp_unregister_congestion_control(&tcp_bbr_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_LICENSE("Dual BSD/GPL");
+MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");