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linux-zen-desktop/net/ipv4/tcp_bbr.c

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/* BBR (Bottleneck Bandwidth and RTT) congestion control
*
* BBR 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 shallow-threshold 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/btf.h>
#include <linux/btf_ids.h>
#include <linux/module.h>
#include <net/tcp.h>
#include <linux/inet_diag.h>
#include <linux/inet.h>
#include <linux/random.h>
#include <linux/win_minmax.h>
#include <trace/events/tcp.h>
#include "tcp_dctcp.h"
#define BBR_VERSION 3
#define bbr_param(sk,name) (bbr_ ## name)
/* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth
* estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps.
* This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32.
* Since the minimum window is >=4 packets, the lower bound isn't
* an issue. The upper bound isn't an issue with existing technologies.
*/
#define BW_SCALE 24
#define BW_UNIT (1 << BW_SCALE)
#define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) */
#define BBR_UNIT (1 << BBR_SCALE)
/* BBR has the following modes for deciding how fast to send: */
enum bbr_mode {
BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */
BBR_DRAIN, /* drain any queue created during startup */
BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */
BBR_PROBE_RTT, /* cut inflight to min to probe min_rtt */
};
/* 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 probe_rtt_win_ms win */
u32 probe_rtt_min_stamp; /* timestamp of probe_rtt_min_us*/
u32 next_rtt_delivered; /* scb->tx.delivered at end of round */
u64 cycle_mstamp; /* time of this cycle phase start */
u32 mode:2, /* current bbr_mode in state machine */
prev_ca_state:3, /* CA state on previous ACK */
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? */
idle_restart:1, /* restarting after idle? */
probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */
init_cwnd:7, /* initial cwnd */
unused_1:10;
u32 pacing_gain:10, /* current gain for setting pacing rate */
cwnd_gain:10, /* current gain for setting cwnd */
full_bw_reached:1, /* reached full bw in Startup? */
full_bw_cnt:2, /* number of rounds without large bw gains */
cycle_idx:2, /* current index in pacing_gain cycle array */
has_seen_rtt:1, /* have we seen an RTT sample yet? */
unused_2:6;
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 v3 state: */
full_bw_now:1, /* recently reached full bw plateau? */
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? */
unused_3:1;
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]; /* max recent measured bw sample */
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 prior_rcv_nxt; /* tp->rcv_nxt when CE state last changed */
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 */
u8 unused_4; /* to preserve alignment */
struct tcp_plb_state plb;
};
struct bbr_context {
u32 sample_bw;
};
/* Window length of min_rtt filter (in sec): */
static const u32 bbr_min_rtt_win_sec = 10;
/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */
static const u32 bbr_probe_rtt_mode_ms = 200;
/* Window length of probe_rtt_min_us filter (in ms), and consequently the
* typical interval between PROBE_RTT mode entries. The default is 5000ms.
* Note that bbr_probe_rtt_win_ms must be <= bbr_min_rtt_win_sec * MSEC_PER_SEC
*/
static const u32 bbr_probe_rtt_win_ms = 5000;
/* Proportion of cwnd to estimated BDP in PROBE_RTT, in units of BBR_UNIT: */
static const u32 bbr_probe_rtt_cwnd_gain = BBR_UNIT * 1 / 2;
/* Use min_rtt to help adapt TSO burst size, with smaller min_rtt resulting
* in bigger TSO bursts. 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 const u32 bbr_tso_rtt_shift = 9;
/* 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 startup_pacing_gain of 4*ln(2) because it's the smallest value
* that will allow a smoothly increasing pacing rate that will double each RTT
* and send the same number of packets per RTT that an un-paced, slow-starting
* Reno or CUBIC flow would:
*/
static const int bbr_startup_pacing_gain = BBR_UNIT * 277 / 100 + 1;
/* The gain for deriving startup cwnd: */
static const int bbr_startup_cwnd_gain = BBR_UNIT * 2;
/* The pacing gain in BBR_DRAIN is calculated to typically drain
* the queue created in BBR_STARTUP in a single round:
*/
static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885;
/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */
static const int bbr_cwnd_gain = BBR_UNIT * 2;
/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */
static const int bbr_pacing_gain[] = {
BBR_UNIT * 5 / 4, /* UP: probe for more available bw */
BBR_UNIT * 91 / 100, /* DOWN: drain queue and/or yield bw */
BBR_UNIT, /* CRUISE: try to use pipe w/ some headroom */
BBR_UNIT, /* REFILL: refill pipe to estimated 100% */
};
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% */
};
/* Try to keep at least this many packets in flight, if things go smoothly. For
* smooth functioning, a sliding window protocol ACKing every other packet
* needs at least 4 packets in flight:
*/
static const u32 bbr_cwnd_min_target = 4;
/* To estimate if BBR_STARTUP or BBR_BW_PROBE_UP has filled pipe... */
/* If bw has increased significantly (1.25x), there may be more bw available: */
static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4;
/* But after 3 rounds w/o significant bw growth, estimate pipe is full: */
static const u32 bbr_full_bw_cnt = 3;
/* Gain factor for adding extra_acked to target cwnd: */
static const int bbr_extra_acked_gain = BBR_UNIT;
/* Window length of extra_acked window. */
static const u32 bbr_extra_acked_win_rtts = 5;
/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */
static const u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20;
/* Time period for clamping cwnd increment due to ack aggregation */
static const u32 bbr_extra_acked_max_us = 100 * 1000;
/* Flags to control BBR ECN-related behavior... */
/* Ensure ACKs only ACK packets with consistent ECN CE status? */
static const bool bbr_precise_ece_ack = true;
/* Max RTT (in usec) at which to use sender-side ECN logic.
* Disabled when 0 (ECN allowed at any RTT).
*/
static const u32 bbr_ecn_max_rtt_us = 5000;
/* On losses, scale down inflight and pacing rate by beta scaled by BBR_SCALE.
* No loss response when 0.
*/
static const u32 bbr_beta = BBR_UNIT * 30 / 100;
/* Gain factor for ECN mark ratio samples, scaled by BBR_SCALE (1/16 = 6.25%) */
static const u32 bbr_ecn_alpha_gain = BBR_UNIT * 1 / 16;
/* The initial value for ecn_alpha; 1.0 allows a flow to respond quickly
* to congestion if the bottleneck is congested when the flow starts up.
*/
static const u32 bbr_ecn_alpha_init = BBR_UNIT;
/* On ECN, cut inflight_lo to (1 - ecn_factor * ecn_alpha) scaled by BBR_SCALE.
* No ECN based bounding when 0.
*/
static const 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.
*/
static const u32 bbr_ecn_thresh = BBR_UNIT * 1 / 2; /* 1/2 = 50% */
/* If non-zero, if in a cycle with no losses but some ECN marks, after ECN
* clears then make the first round's increment to inflight_hi the following
* fraction of inflight_hi.
*/
static const u32 bbr_ecn_reprobe_gain = BBR_UNIT * 1 / 2;
/* Estimate bw probing has gone too far if loss rate exceeds this level. */
static const u32 bbr_loss_thresh = BBR_UNIT * 2 / 100; /* 2% loss */
/* Slow down for a packet loss recovered by TLP? */
static const bool bbr_loss_probe_recovery = true;
/* 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.
*/
static const u32 bbr_full_loss_cnt = 6;
/* Exit STARTUP if number of round trips with ECN mark rate above ecn_thresh
* meets this count.
*/
static const u32 bbr_full_ecn_cnt = 2;
/* Fraction of unutilized headroom to try to leave in path upon high loss. */
static const u32 bbr_inflight_headroom = BBR_UNIT * 15 / 100;
/* How much do we increase cwnd_gain when probing for bandwidth in
* BBR_BW_PROBE_UP? This specifies the increment in units of
* BBR_UNIT/4. The default is 1, meaning 0.25.
* The min value is 0 (meaning 0.0); max is 3 (meaning 0.75).
*/
static const u32 bbr_bw_probe_cwnd_gain = 1;
/* 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 const u32 bbr_bw_probe_max_rounds = 63;
/* Max amount of randomness to inject in round counting for Reno-coexistence.
*/
static const 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 const u32 bbr_bw_probe_base_us = 2 * USEC_PER_SEC; /* 2 secs */
/* Use BBR-native probes spread over this many usec: */
static const u32 bbr_bw_probe_rand_us = 1 * USEC_PER_SEC; /* 1 secs */
/* Use fast path if app-limited, no loss/ECN, and target cwnd was reached? */
static const bool bbr_fast_path = true;
/* Use fast ack mode? */
static const bool bbr_fast_ack_mode = true;
static u32 bbr_max_bw(const struct sock *sk);
static u32 bbr_bw(const struct sock *sk);
static void bbr_exit_probe_rtt(struct sock *sk);
static void bbr_reset_congestion_signals(struct sock *sk);
static void bbr_run_loss_probe_recovery(struct sock *sk);
static void bbr_check_probe_rtt_done(struct sock *sk);
/* This connection can use ECN if both endpoints have signaled ECN support in
* the handshake and the per-route settings indicated this is a
* shallow-threshold ECN environment, meaning both:
* (a) ECN CE marks indicate low-latency/shallow-threshold congestion, and
* (b) TCP endpoints provide precise ACKs that only ACK data segments
* with consistent ECN CE status
*/
static bool bbr_can_use_ecn(const struct sock *sk)
{
return (tcp_sk(sk)->ecn_flags & TCP_ECN_OK) &&
(tcp_sk(sk)->ecn_flags & TCP_ECN_LOW);
}
/* 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)
{
const 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)
{
const 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);
}
/* 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: startup_pacing_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)tcp_snd_cwnd(tp) * BW_UNIT;
do_div(bw, rtt_us);
sk->sk_pacing_rate =
bbr_bw_to_pacing_rate(sk, bw, bbr_param(sk, startup_pacing_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;
}
/* Return the number of segments BBR would like in a TSO/GSO skb, given a
* particular max gso size as a constraint. TODO: make this simpler and more
* consistent by switching bbr to just call tcp_tso_autosize().
*/
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_param(sk, tso_rtt_shift)) {
r = bbr->min_rtt_us >> bbr_param(sk, tso_rtt_shift);
if (r < BITS_PER_TYPE(u32)) /* prevent undefined behavior */
bytes += GSO_LEGACY_MAX_SIZE >> r;
}
bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
segs = max_t(u32, bytes / mss_now,
sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
return segs;
}
/* Custom tcp_tso_autosize() for BBR, used at transmit time to cap skb size. */
__bpf_kfunc 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_LEGACY_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 = tcp_snd_cwnd(tp); /* this cwnd is good enough */
else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */
bbr->prior_cwnd = max(bbr->prior_cwnd, tcp_snd_cwnd(tp));
}
__bpf_kfunc 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) {
if (!tp->app_limited)
return;
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_can_use_ecn(sk) &&
bbr_param(sk, precise_ece_ack)) {
u32 state = bbr->ce_state;
dctcp_ece_ack_update(sk, event, &bbr->prior_rcv_nxt, &state);
bbr->ce_state = state;
} else if (event == CA_EVENT_TLP_RECOVERY &&
bbr_param(sk, loss_probe_recovery)) {
bbr_run_loss_probe_recovery(sk);
}
}
/* 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 this won't bloat cwnd because
* in such cases tso_segs_goal is small. 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. */
cwnd = max_t(u32, cwnd, tso_segs_goal);
cwnd = max_t(u32, cwnd, bbr_param(sk, cwnd_min_target));
/* 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)
{
u32 max_aggr_cwnd, aggr_cwnd = 0;
if (bbr_param(sk, extra_acked_gain)) {
max_aggr_cwnd = ((u64)bbr_bw(sk) * bbr_extra_acked_max_us)
/ BW_UNIT;
aggr_cwnd = (bbr_param(sk, 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)
{
return max_t(u32, bbr_param(sk, cwnd_min_target),
bbr_bdp(sk, bbr_bw(sk), bbr_param(sk, 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;
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);
/* 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;
}
cwnd = max_t(u32, cwnd, bbr_param(sk, cwnd_min_target));
done:
tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp)); /* global cap */
if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */
tcp_snd_cwnd_set(tp, min_t(u32, tcp_snd_cwnd(tp),
bbr_probe_rtt_cwnd(sk)));
}
static void bbr_reset_startup_mode(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->mode = BBR_STARTUP;
}
/* See if we have reached next round trip. Upon start of the new round,
* returns packets delivered since previous round start plus this ACK.
*/
static u32 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);
u32 round_delivered = 0;
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)) {
round_delivered = tp->delivered - bbr->next_rtt_delivered;
bbr->next_rtt_delivered = tp->delivered;
bbr->round_start = 1;
}
return round_delivered;
}
/* 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)
{
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;
}
/* 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_param(sk, extra_acked_win_rtts);
if (!bbr_param(sk, 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_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, tcp_snd_cwnd(tp));
if (extra_acked > bbr->extra_acked[bbr->extra_acked_win_idx])
bbr->extra_acked[bbr->extra_acked_win_idx] = extra_acked;
}
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 */
tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp), bbr->prior_cwnd));
bbr_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_param(sk, 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_param(sk, 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_param(sk, 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_param(sk, 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_param(sk, startup_pacing_gain);
bbr->cwnd_gain = bbr_param(sk, startup_cwnd_gain);
break;
case BBR_DRAIN:
bbr->pacing_gain = bbr_param(sk, drain_gain); /* slow, to drain */
bbr->cwnd_gain = bbr_param(sk, startup_cwnd_gain); /* keep cwnd */
break;
case BBR_PROBE_BW:
bbr->pacing_gain = bbr_pacing_gain[bbr->cycle_idx];
bbr->cwnd_gain = bbr_param(sk, cwnd_gain);
if (bbr_param(sk, bw_probe_cwnd_gain) &&
bbr->cycle_idx == BBR_BW_PROBE_UP)
bbr->cwnd_gain +=
BBR_UNIT * bbr_param(sk, bw_probe_cwnd_gain) / 4;
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;
}
}
__bpf_kfunc static u32 bbr_sndbuf_expand(struct sock *sk)
{
/* Provision 3 * cwnd since BBR may slow-start even during recovery. */
return 3;
}
/* Incorporate a new bw sample into the current window of our max filter. */
static void bbr_take_max_bw_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 bbr_advance_max_bw_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;
}
/* Reset the estimator for reaching full bandwidth based on bw plateau. */
static void bbr_reset_full_bw(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->full_bw = 0;
bbr->full_bw_cnt = 0;
bbr->full_bw_now = 0;
}
/* How much do we want in flight? Our BDP, unless congestion cut cwnd. */
static u32 bbr_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 bbr_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 bbr_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 bbr_handle_queue_too_high_in_startup(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 bdp; /* estimated BDP in packets, with quantization budget */
bbr->full_bw_reached = 1;
bdp = bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT);
bbr->inflight_hi = max(bdp, bbr->inflight_latest);
}
/* Exit STARTUP upon N consecutive rounds with ECN mark rate > ecn_thresh. */
static void bbr_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_param(sk, full_ecn_cnt) || !bbr_param(sk, ecn_thresh))
return;
if (ce_ratio >= bbr_param(sk, ecn_thresh))
bbr->startup_ecn_rounds++;
else
bbr->startup_ecn_rounds = 0;
if (bbr->startup_ecn_rounds >= bbr_param(sk, full_ecn_cnt)) {
bbr_handle_queue_too_high_in_startup(sk);
return;
}
}
/* Updates ecn_alpha and returns ce_ratio. -1 if not available. */
static int bbr_update_ecn_alpha(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
struct bbr *bbr = inet_csk_ca(sk);
s32 delivered, delivered_ce;
u64 alpha, ce_ratio;
u32 gain;
bool want_ecn_alpha;
/* See if we should use ECN sender logic for this connection. */
if (!bbr->ecn_eligible && bbr_can_use_ecn(sk) &&
bbr_param(sk, ecn_factor) &&
(bbr->min_rtt_us <= bbr_ecn_max_rtt_us ||
!bbr_ecn_max_rtt_us))
bbr->ecn_eligible = 1;
/* Skip updating alpha only if not ECN-eligible and PLB is disabled. */
want_ecn_alpha = (bbr->ecn_eligible ||
(bbr_can_use_ecn(sk) &&
READ_ONCE(net->ipv4.sysctl_tcp_plb_enabled)));
if (!want_ecn_alpha)
return -1;
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 -1;
BUILD_BUG_ON(BBR_SCALE != TCP_PLB_SCALE);
ce_ratio = (u64)delivered_ce << BBR_SCALE;
do_div(ce_ratio, delivered);
gain = bbr_param(sk, 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;
bbr_check_ecn_too_high_in_startup(sk, ce_ratio);
return (int)ce_ratio;
}
/* Protective Load Balancing (PLB). PLB rehashes outgoing data (to a new IPv6
* flow label) if it encounters sustained congestion in the form of ECN marks.
*/
static void bbr_plb(struct sock *sk, const struct rate_sample *rs, int ce_ratio)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->round_start && ce_ratio >= 0)
tcp_plb_update_state(sk, &bbr->plb, ce_ratio);
tcp_plb_check_rehash(sk, &bbr->plb);
}
/* Each round trip of BBR_BW_PROBE_UP, double volume of probing data. */
static void bbr_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 = tcp_snd_cwnd(tp) / growth_this_round;
cnt = max(cnt, 1U);
bbr->bw_probe_up_cnt = cnt;
}
/* In BBR_BW_PROBE_UP, not seeing high loss/ECN/queue, so raise inflight_hi. */
static void bbr_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 || tcp_snd_cwnd(tp) < bbr->inflight_hi)
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->try_fast_path = 0; /* Need to update cwnd */
}
if (bbr->round_start)
bbr_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 bbr_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_param(sk, loss_thresh) >>
BBR_SCALE;
if (rs->lost > loss_thresh) {
return true;
}
}
if (rs->delivered_ce > 0 && rs->delivered > 0 &&
bbr->ecn_eligible && bbr_param(sk, ecn_thresh)) {
ecn_thresh = (u64)rs->delivered * bbr_param(sk, 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 bbr_inflight_hi_from_lost_skb(const struct sock *sk,
const struct rate_sample *rs,
const struct sk_buff *skb)
{
const struct tcp_sock *tp = tcp_sk(sk);
u32 loss_thresh = bbr_param(sk, 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 (inflight_prev < 0) {
WARN_ONCE(tcp_skb_tx_in_flight_is_suspicious(
pcount,
TCP_SKB_CB(skb)->sacked,
rs->tx_in_flight),
"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_ONCE(lost_prev < 0,
"cwnd: %u ca: %d out: %u lost: %u pif: %u "
"tx_in_flight: %u tx.lost: %u tp->lost: %u rs->lost: %d "
"lost_prev: %d pcount: %d seq: %u end_seq: %u reneg: %u",
tcp_snd_cwnd(tp), inet_csk(sk)->icsk_ca_state,
tp->packets_out, tp->lost_out, tcp_packets_in_flight(tp),
rs->tx_in_flight, TCP_SKB_CB(skb)->tx.lost, tp->lost,
rs->lost, lost_prev, pcount,
TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq,
tp->is_sack_reneg))
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 bbr_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_param(sk, inflight_headroom);
headroom = ((u64)bbr->inflight_hi * headroom_fraction) >> BBR_SCALE;
headroom = max(headroom, 1U);
return max_t(s32, bbr->inflight_hi - headroom,
bbr_param(sk, 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 bbr_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 = bbr_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_param(sk, cwnd_min_target));
tcp_snd_cwnd_set(tp, min(cap, tcp_snd_cwnd(tp)));
}
/* How should we multiplicatively cut bw or inflight limits based on ECN? */
u32 bbr_ecn_cut(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return BBR_UNIT -
((bbr->ecn_alpha * bbr_param(sk, ecn_factor)) >> BBR_SCALE);
}
/* Init lower bounds if have not inited yet. */
static void bbr_init_lower_bounds(struct sock *sk, bool init_bw)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (init_bw && bbr->bw_lo == ~0U)
bbr->bw_lo = bbr_max_bw(sk);
if (bbr->inflight_lo == ~0U)
bbr->inflight_lo = tcp_snd_cwnd(tp);
}
/* Reduce bw and inflight to (1 - beta). */
static void bbr_loss_lower_bounds(struct sock *sk, u32 *bw, u32 *inflight)
{
struct bbr* bbr = inet_csk_ca(sk);
u32 loss_cut = BBR_UNIT - bbr_param(sk, beta);
*bw = max_t(u32, bbr->bw_latest,
(u64)bbr->bw_lo * loss_cut >> BBR_SCALE);
*inflight = max_t(u32, bbr->inflight_latest,
(u64)bbr->inflight_lo * loss_cut >> BBR_SCALE);
}
/* Reduce inflight to (1 - alpha*ecn_factor). */
static void bbr_ecn_lower_bounds(struct sock *sk, u32 *inflight)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 ecn_cut = bbr_ecn_cut(sk);
*inflight = (u64)bbr->inflight_lo * ecn_cut >> BBR_SCALE;
}
/* 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 bbr_adapt_lower_bounds(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 ecn_inflight_lo = ~0U;
/* We only use lower-bound estimates when not probing bw.
* When probing we need to push inflight higher to probe bw.
*/
if (bbr_is_probing_bandwidth(sk))
return;
/* ECN response. */
if (bbr->ecn_in_round && bbr_param(sk, ecn_factor)) {
bbr_init_lower_bounds(sk, false);
bbr_ecn_lower_bounds(sk, &ecn_inflight_lo);
}
/* Loss response. */
if (bbr->loss_in_round) {
bbr_init_lower_bounds(sk, true);
bbr_loss_lower_bounds(sk, &bbr->bw_lo, &bbr->inflight_lo);
}
/* Adjust to the lower of the levels implied by loss/ECN. */
bbr->inflight_lo = min(bbr->inflight_lo, ecn_inflight_lo);
bbr->bw_lo = max(1U, bbr->bw_lo);
}
/* Reset any short-term lower-bound adaptation to congestion, so that we can
* push our inflight up.
*/
static void bbr_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 bbr_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;
}
static void bbr_exit_loss_recovery(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp), bbr->prior_cwnd));
bbr->try_fast_path = 0; /* bound cwnd using latest model */
}
/* Update rate and volume of delivered data from latest round trip. */
static void bbr_update_latest_delivery_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);
bbr->loss_round_start = 0;
if (rs->interval_us <= 0 || !rs->acked_sacked)
return; /* Not a valid observation */
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)) {
bbr->loss_round_delivered = tp->delivered;
bbr->loss_round_start = 1; /* mark start of new round trip */
}
}
/* Once per round, reset filter for latest rate and volume of delivered data. */
static void bbr_advance_latest_delivery_signals(
struct sock *sk, const struct rate_sample *rs, struct bbr_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
/* If ACK matches a TLP retransmit, persist the filter. If we detect
* that a TLP retransmit plugged a tail loss, we'll want to remember
* how much data the path delivered before the tail loss.
*/
if (bbr->loss_round_start && !rs->is_acking_tlp_retrans_seq) {
bbr->bw_latest = ctx->sample_bw;
bbr->inflight_latest = rs->delivered;
}
}
/* 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 bbr_update_congestion_signals(
struct sock *sk, const struct rate_sample *rs, struct bbr_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
u64 bw;
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))
bbr_take_max_bw_sample(sk, bw);
bbr->loss_in_round |= (rs->losses > 0);
if (!bbr->loss_round_start)
return; /* skip the per-round-trip updates */
/* Now do per-round-trip updates. */
bbr_adapt_lower_bounds(sk, rs);
bbr->loss_in_round = 0;
bbr->ecn_in_round = 0;
}
/* 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 bbr_is_reno_coexistence_probe_time(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 rounds;
/* Random loss can shave some small percentage off of our inflight
* in each round. To survive this, flows need robust periodic probes.
*/
rounds = min_t(u32, bbr_param(sk, bw_probe_max_rounds), bbr_target_inflight(sk));
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 bbr_pick_probe_wait(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
/* Decide the random round-trip bound for wait until probe: */
bbr->rounds_since_probe =
get_random_u32_below(bbr_param(sk, bw_probe_rand_rounds));
/* Decide the random wall clock bound for wait until probe: */
bbr->probe_wait_us = bbr_param(sk, bw_probe_base_us) +
get_random_u32_below(bbr_param(sk, bw_probe_rand_us));
}
static void bbr_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 bbr_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);
bbr_reset_lower_bounds(sk);
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;
bbr_set_cycle_idx(sk, BBR_BW_PROBE_REFILL);
}
/* Now probe max deliverable data rate and volume. */
static void bbr_start_bw_probe_up(struct sock *sk, struct bbr_context *ctx)
{
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;
bbr_reset_full_bw(sk);
bbr->full_bw = ctx->sample_bw;
bbr_set_cycle_idx(sk, BBR_BW_PROBE_UP);
bbr_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 bbr_start_bw_probe_down(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr_reset_congestion_signals(sk);
bbr->bw_probe_up_cnt = ~0U; /* not growing inflight_hi any more */
bbr_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;
bbr_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 bbr_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);
bbr_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 bbr_handle_inflight_too_high(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
const u32 beta = bbr_param(sk, beta);
bbr->prev_probe_too_high = 1;
bbr->bw_probe_samples = 0; /* only react once per probe */
/* 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)bbr_target_inflight(sk) *
(BBR_UNIT - beta) >> BBR_SCALE);
}
if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == BBR_BW_PROBE_UP)
bbr_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 bbr_adapt_upper_bounds(struct sock *sk,
const struct rate_sample *rs,
struct bbr_context *ctx)
{
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)
bbr_advance_max_bw_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_start_bw_probe_refill(sk, 0);
return true; /* yes, decided state transition */
}
}
if (bbr_is_inflight_too_high(sk, rs)) {
if (bbr->bw_probe_samples) /* sample is from bw probing? */
bbr_handle_inflight_too_high(sk, rs);
} else {
/* Loss/ECN rate is declared safe. Adjust upper bound upward. */
if (bbr->inflight_hi == ~0U)
return false; /* no excess queue signals yet */
/* To be resilient to random loss, we must raise bw/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;
}
if (bbr->mode == BBR_PROBE_BW &&
bbr->cycle_idx == BBR_BW_PROBE_UP)
bbr_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 bbr_check_time_to_probe_bw(struct sock *sk,
const struct rate_sample *rs)
{
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 cross-traffic has ceased and freed up bw).
*/
if (bbr_param(sk, ecn_reprobe_gain) && bbr->ecn_eligible &&
bbr->ecn_in_cycle && !bbr->loss_in_cycle &&
inet_csk(sk)->icsk_ca_state == TCP_CA_Open) {
/* Calculate n so that when bbr_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_param(sk, ecn_reprobe_gain)) >> BBR_SCALE));
bbr_start_bw_probe_refill(sk, n);
return true;
}
if (bbr_has_elapsed_in_phase(sk, bbr->probe_wait_us) ||
bbr_is_reno_coexistence_probe_time(sk)) {
bbr_start_bw_probe_refill(sk, 0);
return true;
}
return false;
}
/* Is it time to transition from PROBE_DOWN to PROBE_CRUISE? */
static bool bbr_check_time_to_cruise(struct sock *sk, u32 inflight, u32 bw)
{
/* Always need to pull inflight down to leave headroom in queue. */
if (inflight > bbr_inflight_with_headroom(sk))
return false;
return inflight <= bbr_inflight(sk, bw, BBR_UNIT);
}
/* PROBE_BW state machine: cruise, refill, probe for bw, or drain? */
static void bbr_update_cycle_phase(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);
bool is_bw_probe_done = false;
u32 inflight, bw;
if (!bbr_full_bw_reached(sk))
return;
/* In DRAIN, PROBE_BW, or PROBE_RTT, adjust upper bounds. */
if (bbr_adapt_upper_bounds(sk, rs, ctx))
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 (bbr_check_time_to_probe_bw(sk, rs))
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;
bbr_start_bw_probe_up(sk, ctx);
}
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.
* (2) If inflight_hi has not limited bandwidth growth recently, and
* yet delivered bandwidth has not increased much recently
* (bbr->full_bw_now).
* (3) Loss filter says loss rate is "too high".
* (4) ECN filter says ECN mark rate is "too high".
*
* (1) (2) checked here, (3) (4) 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_bw_probe_done = true;
} else {
if (tp->is_cwnd_limited &&
tcp_snd_cwnd(tp) >= bbr->inflight_hi) {
/* inflight_hi is limiting bw growth */
bbr_reset_full_bw(sk);
bbr->full_bw = ctx->sample_bw;
} else if (bbr->full_bw_now) {
/* Plateau in estimated bw. Pipe looks full. */
is_bw_probe_done = true;
}
}
if (is_bw_probe_done) {
bbr->prev_probe_too_high = 0; /* no loss/ECN (yet) */
bbr_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 (bbr_check_time_to_probe_bw(sk, rs))
return; /* already decided state transition */
if (bbr_check_time_to_cruise(sk, inflight, bw))
bbr_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 bbr_exit_probe_rtt(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr_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.
*/
bbr_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.
*/
bbr_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 bbr_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_param(sk, full_loss_cnt) && bbr->loss_round_start &&
inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery &&
bbr->loss_events_in_round >= bbr_param(sk, full_loss_cnt) &&
bbr_is_inflight_too_high(sk, rs)) {
bbr_handle_queue_too_high_in_startup(sk);
return;
}
if (bbr->loss_round_start)
bbr->loss_events_in_round = 0;
}
/* Estimate when the pipe is full, using the change in delivery rate: BBR
* estimates bw probing 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_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 bw_thresh, full_cnt, thresh;
if (bbr->full_bw_now || rs->is_app_limited)
return;
thresh = bbr_param(sk, full_bw_thresh);
full_cnt = bbr_param(sk, full_bw_cnt);
bw_thresh = (u64)bbr->full_bw * thresh >> BBR_SCALE;
if (ctx->sample_bw >= bw_thresh) {
bbr_reset_full_bw(sk);
bbr->full_bw = ctx->sample_bw;
return;
}
if (!bbr->round_start)
return;
++bbr->full_bw_cnt;
bbr->full_bw_now = bbr->full_bw_cnt >= full_cnt;
bbr->full_bw_reached |= bbr->full_bw_now;
}
/* If pipe is probably full, drain the queue and then enter steady-state. */
static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs,
struct bbr_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 */
/* Set ssthresh to export purely for monitoring, to signal
* completion of initial STARTUP by setting to a non-
* TCP_INFINITE_SSTHRESH value (ssthresh is not used by BBR).
*/
tcp_sk(sk)->snd_ssthresh =
bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT);
bbr_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)) {
bbr->mode = BBR_PROBE_BW;
bbr_start_bw_probe_down(sk);
}
}
static void bbr_update_model(struct sock *sk, const struct rate_sample *rs,
struct bbr_context *ctx)
{
bbr_update_congestion_signals(sk, rs, ctx);
bbr_update_ack_aggregation(sk, rs);
bbr_check_loss_too_high_in_startup(sk, rs);
bbr_check_full_bw_reached(sk, rs, ctx);
bbr_check_drain(sk, rs, ctx);
bbr_update_cycle_phase(sk, rs, ctx);
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 bbr_run_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_param(sk, 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;
bbr_check_drain(sk, rs, ctx);
bbr_update_cycle_phase(sk, rs, ctx);
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;
}
__bpf_kfunc void bbr_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, round_delivered;
int ce_ratio = -1;
round_delivered = bbr_update_round_start(sk, rs, &ctx);
if (bbr->round_start) {
bbr->rounds_since_probe =
min_t(s32, bbr->rounds_since_probe + 1, 0xFF);
ce_ratio = bbr_update_ecn_alpha(sk);
}
bbr_plb(sk, rs, ce_ratio);
bbr->ecn_in_round |= (bbr->ecn_eligible && rs->is_ece);
bbr_calculate_bw_sample(sk, rs, &ctx);
bbr_update_latest_delivery_signals(sk, rs, &ctx);
if (bbr_run_fast_path(sk, &update_model, rs, &ctx))
goto out;
if (update_model)
bbr_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,
tcp_snd_cwnd(tp), &ctx);
bbr_bound_cwnd_for_inflight_model(sk);
out:
bbr_advance_latest_delivery_signals(sk, rs, &ctx);
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;
}
__bpf_kfunc static void bbr_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr->initialized = 1;
bbr->init_cwnd = min(0x7FU, tcp_snd_cwnd(tp));
bbr->prior_cwnd = tp->prior_cwnd;
tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
bbr->next_rtt_delivered = tp->delivered;
bbr->prev_ca_state = TCP_CA_Open;
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_reset_startup_mode(sk);
bbr->ack_epoch_mstamp = tp->tcp_mstamp;
bbr->ack_epoch_acked = 0;
bbr->extra_acked_win_rtts = 0;
bbr->extra_acked_win_idx = 0;
bbr->extra_acked[0] = 0;
bbr->extra_acked[1] = 0;
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);
/* 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;
bbr_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_reset_full_bw(sk);
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_param(sk, ecn_alpha_init);
bbr->alpha_last_delivered = 0;
bbr->alpha_last_delivered_ce = 0;
bbr->plb.pause_until = 0;
tp->fast_ack_mode = bbr_fast_ack_mode ? 1 : 0;
if (bbr_can_use_ecn(sk))
tp->ecn_flags |= TCP_ECN_ECT_PERMANENT;
}
/* BBR marks the current round trip as a loss round. */
static void bbr_note_loss(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
/* Capture "current" data over the full round trip of loss, to
* have a better chance of observing 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;
}
/* Core TCP stack informs us that the given skb was just marked lost. */
__bpf_kfunc static void bbr_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 = {};
bbr_note_loss(sk);
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.
*/
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 (bbr_is_inflight_too_high(sk, &rs)) {
rs.tx_in_flight = bbr_inflight_hi_from_lost_skb(sk, &rs, skb);
bbr_handle_inflight_too_high(sk, &rs);
}
}
static void bbr_run_loss_probe_recovery(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
struct rate_sample rs = {0};
bbr_note_loss(sk);
if (!bbr->bw_probe_samples)
return; /* not sent while probing for bandwidth */
/* We are probing for bandwidth. Construct a rate sample that
* estimates what happened in the flight leading up to this
* loss, then see if the loss rate went too high.
*/
rs.lost = 1; /* TLP probe repaired loss of a single segment */
rs.tx_in_flight = bbr->inflight_latest + rs.lost;
rs.is_app_limited = tp->tlp_orig_data_app_limited;
if (bbr_is_inflight_too_high(sk, &rs))
bbr_handle_inflight_too_high(sk, &rs);
}
/* Revert short-term model if current loss recovery event was spurious. */
__bpf_kfunc static u32 bbr_undo_cwnd(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr_reset_full_bw(sk); /* spurious slow-down; reset full bw detector */
bbr->loss_in_round = 0;
/* 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);
bbr->try_fast_path = 0; /* take slow path to set proper cwnd, pacing */
return bbr->prior_cwnd;
}
/* Entering loss recovery, so save state for when we undo recovery. */
__bpf_kfunc static u32 bbr_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_bbr_phase bbr_get_phase(struct bbr *bbr)
{
switch (bbr->mode) {
case BBR_STARTUP:
return BBR_PHASE_STARTUP;
case BBR_DRAIN:
return BBR_PHASE_DRAIN;
case BBR_PROBE_BW:
break;
case BBR_PROBE_RTT:
return BBR_PHASE_PROBE_RTT;
default:
return BBR_PHASE_INVALID;
}
switch (bbr->cycle_idx) {
case BBR_BW_PROBE_UP:
return BBR_PHASE_PROBE_BW_UP;
case BBR_BW_PROBE_DOWN:
return BBR_PHASE_PROBE_BW_DOWN;
case BBR_BW_PROBE_CRUISE:
return BBR_PHASE_PROBE_BW_CRUISE;
case BBR_BW_PROBE_REFILL:
return BBR_PHASE_PROBE_BW_REFILL;
default:
return BBR_PHASE_INVALID;
}
}
static size_t bbr_get_info(struct sock *sk, u32 ext, int *attr,
union tcp_cc_info *info)
{
if (ext & (1 << (INET_DIAG_BBRINFO - 1)) ||
ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
struct 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);
struct tcp_bbr_info *bbr_info = &info->bbr;
memset(bbr_info, 0, sizeof(*bbr_info));
bbr_info->bbr_bw_lo = (u32)bw;
bbr_info->bbr_bw_hi = (u32)(bw >> 32);
bbr_info->bbr_min_rtt = bbr->min_rtt_us;
bbr_info->bbr_pacing_gain = bbr->pacing_gain;
bbr_info->bbr_cwnd_gain = bbr->cwnd_gain;
bbr_info->bbr_bw_hi_lsb = (u32)bw_hi;
bbr_info->bbr_bw_hi_msb = (u32)(bw_hi >> 32);
bbr_info->bbr_bw_lo_lsb = (u32)bw_lo;
bbr_info->bbr_bw_lo_msb = (u32)(bw_lo >> 32);
bbr_info->bbr_mode = bbr->mode;
bbr_info->bbr_phase = (__u8)bbr_get_phase(bbr);
bbr_info->bbr_version = (__u8)BBR_VERSION;
bbr_info->bbr_inflight_lo = bbr->inflight_lo;
bbr_info->bbr_inflight_hi = bbr->inflight_hi;
bbr_info->bbr_extra_acked = bbr_extra_acked(sk);
*attr = INET_DIAG_BBRINFO;
return sizeof(*bbr_info);
}
return 0;
}
__bpf_kfunc static void bbr_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) {
bbr->prev_ca_state = TCP_CA_Loss;
tcp_plb_update_state_upon_rto(sk, &bbr->plb);
/* The tcp_write_timeout() call to sk_rethink_txhash() likely
* repathed this flow, so re-learn the min network RTT on the
* new path:
*/
bbr_reset_full_bw(sk);
if (!bbr_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(tcp_snd_cwnd(tp), bbr->prior_cwnd);
}
} else if (bbr->prev_ca_state == TCP_CA_Loss &&
new_state != TCP_CA_Loss) {
bbr_exit_loss_recovery(sk);
}
}
static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
.flags = TCP_CONG_NON_RESTRICTED | TCP_CONG_WANTS_CE_EVENTS,
.name = "bbr",
.owner = THIS_MODULE,
.init = bbr_init,
.cong_control = bbr_main,
.sndbuf_expand = bbr_sndbuf_expand,
.skb_marked_lost = bbr_skb_marked_lost,
.undo_cwnd = bbr_undo_cwnd,
.cwnd_event = bbr_cwnd_event,
.ssthresh = bbr_ssthresh,
.tso_segs = bbr_tso_segs,
.get_info = bbr_get_info,
.set_state = bbr_set_state,
};
BTF_SET8_START(tcp_bbr_check_kfunc_ids)
#ifdef CONFIG_X86
#ifdef CONFIG_DYNAMIC_FTRACE
BTF_ID_FLAGS(func, bbr_init)
BTF_ID_FLAGS(func, bbr_main)
BTF_ID_FLAGS(func, bbr_sndbuf_expand)
BTF_ID_FLAGS(func, bbr_skb_marked_lost)
BTF_ID_FLAGS(func, bbr_undo_cwnd)
BTF_ID_FLAGS(func, bbr_cwnd_event)
BTF_ID_FLAGS(func, bbr_ssthresh)
BTF_ID_FLAGS(func, bbr_tso_segs)
BTF_ID_FLAGS(func, bbr_set_state)
#endif
#endif
BTF_SET8_END(tcp_bbr_check_kfunc_ids)
static const struct btf_kfunc_id_set tcp_bbr_kfunc_set = {
.owner = THIS_MODULE,
.set = &tcp_bbr_check_kfunc_ids,
};
static int __init bbr_register(void)
{
int ret;
BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);
ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_bbr_kfunc_set);
if (ret < 0)
return ret;
return tcp_register_congestion_control(&tcp_bbr_cong_ops);
}
static void __exit bbr_unregister(void)
{
tcp_unregister_congestion_control(&tcp_bbr_cong_ops);
}
module_init(bbr_register);
module_exit(bbr_unregister);
MODULE_AUTHOR("Van Jacobson <vanj@google.com>");
MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>");
MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>");
MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>");
MODULE_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_AUTHOR("David Morley <morleyd@google.com>");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");
MODULE_VERSION(__stringify(BBR_VERSION));
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