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openmptcprouter/patches/bbr2-5.15.patch
Ycarus (Yannick Chabanois) ceef6a6797 Update BBR patch
2022-09-11 19:25:49 +02:00

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diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index b06c2d02ec84e..2cdc5a0709fe0 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -134,8 +134,9 @@ struct inet_connection_sock {
u32 icsk_probes_tstamp;
u32 icsk_user_timeout;
- u64 icsk_ca_priv[104 / sizeof(u64)];
-#define ICSK_CA_PRIV_SIZE sizeof_field(struct inet_connection_sock, icsk_ca_priv)
+/* XXX inflated by temporary internal debugging info */
+#define ICSK_CA_PRIV_SIZE (216)
+ u64 icsk_ca_priv[ICSK_CA_PRIV_SIZE / sizeof(u64)];
};
#define ICSK_TIME_RETRANS 1 /* Retransmit timer */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 82389ead6304e..fa924be339a98 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -371,6 +371,7 @@ 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,
diff --git a/include/uapi/linux/inet_diag.h b/include/uapi/linux/inet_diag.h
index 20ee93f0f8761..96d52dd9c48ac 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 87983e70f03f3..a833a7a67ce79 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -669,6 +669,24 @@ 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
@@ -706,6 +724,9 @@ 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
@@ -730,6 +751,7 @@ 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 bbdd9c44f14e3..8dee1547d8202 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_bbr2.c b/net/ipv4/tcp_bbr2.c
new file mode 100644
index 0000000000000..fa49e17c47ca9
--- /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] */
+ (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, 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 =
+ prandom_u32_max(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 +
+ prandom_u32_max(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/include/net/tcp.h b/include/net/tcp.h
index c87291dd64a76..0c55d57e4b835 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -874,10 +874,11 @@ struct tcp_skb_cb {
__u32 ack_seq; /* Sequence number ACK'd */
union {
struct {
+#define TCPCB_DELIVERED_CE_MASK ((1U<<20) - 1)
/* There is space for up to 24 bytes */
- __u32 in_flight:30,/* Bytes in flight at transmit */
- is_app_limited:1, /* cwnd not fully used? */
+ __u32 is_app_limited:1, /* cwnd not fully used? */
- unused:1;
+ delivered_ce:20,
+ unused:11;
/* pkts S/ACKed so far upon tx of skb, incl retrans: */
__u32 delivered;
/* start of send pipeline phase */
@@ -1028,7 +1030,9 @@ struct ack_sample {
struct rate_sample {
u64 prior_mstamp; /* starting timestamp for interval */
u32 prior_delivered; /* tp->delivered at "prior_mstamp" */
+ u32 prior_delivered_ce;/* tp->delivered_ce at "prior_mstamp" */
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" */
u32 snd_interval_us; /* snd interval for delivered packets */
u32 rcv_interval_us; /* rcv interval for delivered packets */
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index 0de6935659635..fbab921670cc9 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -65,6 +65,7 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
TCP_SKB_CB(skb)->tx.first_tx_mstamp = tp->first_tx_mstamp;
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.is_app_limited = tp->app_limited ? 1 : 0;
}
@@ -138,6 +140,10 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
}
rs->delivered = tp->delivered - rs->prior_delivered;
+ rs->delivered_ce = tp->delivered_ce - rs->prior_delivered_ce;
+ /* delivered_ce occupies less than 32 bits in the skb control block */
+ rs->delivered_ce &= TCPCB_DELIVERED_CE_MASK;
+
/* Model sending data and receiving ACKs as separate pipeline phases
* for a window. Usually the ACK phase is longer, but with ACK
* compression the send phase can be longer. To be safe we use the
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3437789f10e93..da11fde1610fd 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -377,7 +377,8 @@ 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);
}
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index 7ac8aa4a0a367..c657923d2233d 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -111,17 +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->tx_in_flight = scb->tx.in_flight;
rs->last_end_seq = scb->end_seq;
/* 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
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0c55d57e4b835..65e39dc90c7ba 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -807,6 +807,11 @@ 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);
@@ -882,9 +887,9 @@ 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;
} tx; /* only used for outgoing skbs */
union {
struct inet_skb_parm h4;
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index fbab921670cc9..b64d82481ae93 100644
@@ -150,7 +151,7 @@ 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/include/net/tcp.h b/include/net/tcp.h
index 65e39dc90c7ba..b6f667a268ee9 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -890,6 +890,10 @@ struct tcp_skb_cb {
u32 first_tx_mstamp;
/* when we reached the "delivered" count */
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;
} tx; /* only used for outgoing skbs */
union {
struct inet_skb_parm h4;
@@ -1036,6 +1040,7 @@ struct rate_sample {
u64 prior_mstamp; /* starting timestamp for interval */
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 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" */
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index b64d82481ae93..3ecc831206b58 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -40,6 +40,7 @@
void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
+ u32 in_flight;
/* In general we need to start delivery rate samples from the
* time we received the most recent ACK, to ensure we include
@@ -67,6 +68,18 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
TCP_SKB_CB(skb)->tx.delivered = tp->delivered;
TCP_SKB_CB(skb)->tx.delivered_ce = tp->delivered_ce;
TCP_SKB_CB(skb)->tx.is_app_limited = tp->app_limited ? 1 : 0;
+
+ /* Check, sanitize, and record packets in flight after skb was sent. */
+ in_flight = tcp_packets_in_flight(tp) + tcp_skb_pcount(skb);
+ 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 = min(in_flight, TCPCB_IN_FLIGHT_MAX);
+ TCP_SKB_CB(skb)->tx.in_flight = in_flight;
}
/* When an skb is sacked or acked, we fill in the rate sample with the (prior)
#@@ -92,6 +105,7 @@ void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
# rs->prior_mstamp = scb->tx.delivered_mstamp;
# rs->is_app_limited = scb->tx.is_app_limited;
# rs->is_retrans = scb->sacked & TCPCB_RETRANS;
#+ rs->tx_in_flight = scb->tx.in_flight;
#
# /* Record send time of most recently ACKed packet: */
# tp->first_tx_mstamp = tcp_skb_timestamp_us(skb);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index b6f667a268ee9..61782eedb55de 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -894,6 +894,7 @@ struct tcp_skb_cb {
#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;
@@ -1038,11 +1039,13 @@ 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*/
+ s32 delivered_ce; /* packets delivered w/ CE mark over interval */
long interval_us; /* time for tp->delivered to incr "delivered" */
u32 snd_interval_us; /* snd interval for delivered packets */
u32 rcv_interval_us; /* rcv interval for delivered packets */
diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index 3ecc831206b58..f454fce5e1fd9 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -67,6 +67,7 @@ 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;
/* Check, sanitize, and record packets in flight after skb was sent. */
@@ -154,6 +156,7 @@ 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 */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 71e60a4e373cc..9580ef2b099c4 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1172,6 +1172,7 @@ static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
}
/* 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/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index f454fce5e1fd9..796fa6e5310ce 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -34,13 +34,30 @@
* 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().
*/
void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
- u32 in_flight;
/* In general we need to start delivery rate samples from the
* time we received the most recent ACK, to ensure we include
@@ -69,18 +86,7 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
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;
-
- /* Check, sanitize, and record packets in flight after skb was sent. */
- in_flight = tcp_packets_in_flight(tp) + tcp_skb_pcount(skb);
- 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 = min(in_flight, TCPCB_IN_FLIGHT_MAX);
- TCP_SKB_CB(skb)->tx.in_flight = in_flight;
+ tcp_set_tx_in_flight(sk, skb);
}
/* When an skb is sacked or acked, we fill in the rate sample with the (prior)
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 48d8a363319e5..1bd559c69e839 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -225,7 +225,8 @@ 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/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f5c336f8b0c8e..7de20f142443c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3044,6 +3044,7 @@ 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_cong.c b/net/ipv4/tcp_cong.c
index db5831e6c136a..153ed9010c0c2 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -179,6 +179,7 @@ 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 d85ce5cf94995..425014b2c9207 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5463,13 +5463,14 @@ 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/include/net/tcp.h b/include/net/tcp.h
index 61782eedb55de..244798d8dcac8 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1056,6 +1056,7 @@ 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 {
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 71e6baca8cf1c..10516595f379d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3878,6 +3878,7 @@ 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);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 9580ef2b099c4..f22999a698a28 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1019,7 +1019,11 @@ 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;
@@ -1147,6 +1151,14 @@ 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);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0b3db3ceee092..d85ce5cf94995 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;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 244798d8dcac8..71e60a4e373cc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1083,6 +1083,9 @@ struct tcp_congestion_ops {
/* override sysctl_tcp_min_tso_segs */
u32 (*min_tso_segs)(struct sock *sk);
+ /* 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)
*/
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 10516595f379d..94ad315d8ab94 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1071,7 +1071,12 @@ 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)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index f22999a698a28..82389ead6304e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1084,8 +1084,8 @@ 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);
diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
index 0dcee9df13268..503eb58c67870 100644
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -20,7 +20,7 @@ static u32 optional_ops[] = {
offsetof(struct tcp_congestion_ops, cwnd_event),
offsetof(struct tcp_congestion_ops, in_ack_event),
offsetof(struct tcp_congestion_ops, pkts_acked),
- offsetof(struct tcp_congestion_ops, min_tso_segs),
+ offsetof(struct tcp_congestion_ops, tso_segs),
offsetof(struct tcp_congestion_ops, sndbuf_expand),
offsetof(struct tcp_congestion_ops, cong_control),
};
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 6274462b86b4b..c0d5a4211fc18 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -292,26 +292,40 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
sk->sk_pacing_rate = rate;
}
-/* override sysctl_tcp_min_tso_segs */
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, 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_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_MAX_SIZE);
}
/* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
@@ -1147,7 +1161,7 @@ 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_output.c b/net/ipv4/tcp_output.c
index d9f1b83be6047..3437789f10e93 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1990,13 +1990,12 @@ 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;
+ u32 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);
-
- 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);
}
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