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linux-zen-server/net/ipv4/tcp_bbr2.c

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Initial commit
2023-08-30 17:53:23 +02:00
/* BBR (Bottleneck Bandwidth and RTT) congestion control, v2
*
* BBRv2 is a model-based congestion control algorithm that aims for low
* queues, low loss, and (bounded) Reno/CUBIC coexistence. To maintain a model
* of the network path, it uses measurements of bandwidth and RTT, as well as
* (if they occur) packet loss and/or DCTCP/L4S-style ECN signals. Note that
* although it can use ECN or loss signals explicitly, it does not require
* either; it can bound its in-flight data based on its estimate of the BDP.
*
* The model has both higher and lower bounds for the operating range:
* lo: bw_lo, inflight_lo: conservative short-term lower bound
* hi: bw_hi, inflight_hi: robust long-term upper bound
* The bandwidth-probing time scale is (a) extended dynamically based on
* estimated BDP to improve coexistence with Reno/CUBIC; (b) bounded by
* an interactive wall-clock time-scale to be more scalable and responsive
* than Reno and CUBIC.
*
* Here is a state transition diagram for BBR:
*
* |
* V
* +---> STARTUP ----+
* | | |
* | V |
* | DRAIN ----+
* | | |
* | V |
* +---> PROBE_BW ----+
* | ^ | |
* | | | |
* | +----+ |
* | |
* +---- PROBE_RTT <--+
*
* A BBR flow starts in STARTUP, and ramps up its sending rate quickly.
* When it estimates the pipe is full, it enters DRAIN to drain the queue.
* In steady state a BBR flow only uses PROBE_BW and PROBE_RTT.
* A long-lived BBR flow spends the vast majority of its time remaining
* (repeatedly) in PROBE_BW, fully probing and utilizing the pipe's bandwidth
* in a fair manner, with a small, bounded queue. *If* a flow has been
* continuously sending for the entire min_rtt window, and hasn't seen an RTT
* sample that matches or decreases its min_rtt estimate for 10 seconds, then
* it briefly enters PROBE_RTT to cut inflight to a minimum value to re-probe
* the path's two-way propagation delay (min_rtt). When exiting PROBE_RTT, if
* we estimated that we reached the full bw of the pipe then we enter PROBE_BW;
* otherwise we enter STARTUP to try to fill the pipe.
*
* BBR is described in detail in:
* "BBR: Congestion-Based Congestion Control",
* Neal Cardwell, Yuchung Cheng, C. Stephen Gunn, Soheil Hassas Yeganeh,
* Van Jacobson. ACM Queue, Vol. 14 No. 5, September-October 2016.
*
* There is a public e-mail list for discussing BBR development and testing:
* https://groups.google.com/forum/#!forum/bbr-dev
*
* NOTE: BBR might be used with the fq qdisc ("man tc-fq") with pacing enabled,
* otherwise TCP stack falls back to an internal pacing using one high
* resolution timer per TCP socket and may use more resources.
*/
#include <linux/module.h>
#include <net/tcp.h>
#include <linux/inet_diag.h>
#include <linux/inet.h>
#include <linux/random.h>
#include "tcp_dctcp.h"
/* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth
* estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps.
* This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32.
* Since the minimum window is >=4 packets, the lower bound isn't
* an issue. The upper bound isn't an issue with existing technologies.
*/
#define BW_SCALE 24
#define BW_UNIT (1 << BW_SCALE)
#define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) */
#define BBR_UNIT (1 << BBR_SCALE)
#define FLAG_DEBUG_VERBOSE 0x1 /* Verbose debugging messages */
#define FLAG_DEBUG_LOOPBACK 0x2 /* Do NOT skip loopback addr */
#define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */
/* BBR has the following modes for deciding how fast to send: */
enum bbr_mode {
BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */
BBR_DRAIN, /* drain any queue created during startup */
BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */
BBR_PROBE_RTT, /* cut inflight to min to probe min_rtt */
};
/* How does the incoming ACK stream relate to our bandwidth probing? */
enum bbr_ack_phase {
BBR_ACKS_INIT, /* not probing; not getting probe feedback */
BBR_ACKS_REFILLING, /* sending at est. bw to fill pipe */
BBR_ACKS_PROBE_STARTING, /* inflight rising to probe bw */
BBR_ACKS_PROBE_FEEDBACK, /* getting feedback from bw probing */
BBR_ACKS_PROBE_STOPPING, /* stopped probing; still getting feedback */
};
/* BBR congestion control block */
struct bbr {
u32 min_rtt_us; /* min RTT in min_rtt_win_sec window */
u32 min_rtt_stamp; /* timestamp of min_rtt_us */
u32 probe_rtt_done_stamp; /* end time for BBR_PROBE_RTT mode */
u32 probe_rtt_min_us; /* min RTT in bbr_probe_rtt_win_ms window */
u32 probe_rtt_min_stamp; /* timestamp of probe_rtt_min_us*/
u32 next_rtt_delivered; /* scb->tx.delivered at end of round */
u32 prior_rcv_nxt; /* tp->rcv_nxt when CE state last changed */
u64 cycle_mstamp; /* time of this cycle phase start */
u32 mode:3, /* current bbr_mode in state machine */
prev_ca_state:3, /* CA state on previous ACK */
packet_conservation:1, /* use packet conservation? */
round_start:1, /* start of packet-timed tx->ack round? */
ce_state:1, /* If most recent data has CE bit set */
bw_probe_up_rounds:5, /* cwnd-limited rounds in PROBE_UP */
try_fast_path:1, /* can we take fast path? */
unused2:11,
idle_restart:1, /* restarting after idle? */
probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */
cycle_idx:3, /* current index in pacing_gain cycle array */
has_seen_rtt:1; /* have we seen an RTT sample yet? */
u32 pacing_gain:11, /* current gain for setting pacing rate */
cwnd_gain:11, /* current gain for setting cwnd */
full_bw_reached:1, /* reached full bw in Startup? */
full_bw_cnt:2, /* number of rounds without large bw gains */
init_cwnd:7; /* initial cwnd */
u32 prior_cwnd; /* prior cwnd upon entering loss recovery */
u32 full_bw; /* recent bw, to estimate if pipe is full */
/* For tracking ACK aggregation: */
u64 ack_epoch_mstamp; /* start of ACK sampling epoch */
u16 extra_acked[2]; /* max excess data ACKed in epoch */
u32 ack_epoch_acked:20, /* packets (S)ACKed in sampling epoch */
extra_acked_win_rtts:5, /* age of extra_acked, in round trips */
extra_acked_win_idx:1, /* current index in extra_acked array */
/* BBR v2 state: */
unused1:2,
startup_ecn_rounds:2, /* consecutive hi ECN STARTUP rounds */
loss_in_cycle:1, /* packet loss in this cycle? */
ecn_in_cycle:1; /* ECN in this cycle? */
u32 loss_round_delivered; /* scb->tx.delivered ending loss round */
u32 undo_bw_lo; /* bw_lo before latest losses */
u32 undo_inflight_lo; /* inflight_lo before latest losses */
u32 undo_inflight_hi; /* inflight_hi before latest losses */
u32 bw_latest; /* max delivered bw in last round trip */
u32 bw_lo; /* lower bound on sending bandwidth */
u32 bw_hi[2]; /* upper bound of sending bandwidth range*/
u32 inflight_latest; /* max delivered data in last round trip */
u32 inflight_lo; /* lower bound of inflight data range */
u32 inflight_hi; /* upper bound of inflight data range */
u32 bw_probe_up_cnt; /* packets delivered per inflight_hi incr */
u32 bw_probe_up_acks; /* packets (S)ACKed since inflight_hi incr */
u32 probe_wait_us; /* PROBE_DOWN until next clock-driven probe */
u32 ecn_eligible:1, /* sender can use ECN (RTT, handshake)? */
ecn_alpha:9, /* EWMA delivered_ce/delivered; 0..256 */
bw_probe_samples:1, /* rate samples reflect bw probing? */
prev_probe_too_high:1, /* did last PROBE_UP go too high? */
stopped_risky_probe:1, /* last PROBE_UP stopped due to risk? */
rounds_since_probe:8, /* packet-timed rounds since probed bw */
loss_round_start:1, /* loss_round_delivered round trip? */
loss_in_round:1, /* loss marked in this round trip? */
ecn_in_round:1, /* ECN marked in this round trip? */
ack_phase:3, /* bbr_ack_phase: meaning of ACKs */
loss_events_in_round:4,/* losses in STARTUP round */
initialized:1; /* has bbr_init() been called? */
u32 alpha_last_delivered; /* tp->delivered at alpha update */
u32 alpha_last_delivered_ce; /* tp->delivered_ce at alpha update */
/* Params configurable using setsockopt. Refer to correspoding
* module param for detailed description of params.
*/
struct bbr_params {
u32 high_gain:11, /* max allowed value: 2047 */
drain_gain:10, /* max allowed value: 1023 */
cwnd_gain:11; /* max allowed value: 2047 */
u32 cwnd_min_target:4, /* max allowed value: 15 */
min_rtt_win_sec:5, /* max allowed value: 31 */
probe_rtt_mode_ms:9, /* max allowed value: 511 */
full_bw_cnt:3, /* max allowed value: 7 */
cwnd_tso_budget:1, /* allowed values: {0, 1} */
unused3:6,
drain_to_target:1, /* boolean */
precise_ece_ack:1, /* boolean */
extra_acked_in_startup:1, /* allowed values: {0, 1} */
fast_path:1; /* boolean */
u32 full_bw_thresh:10, /* max allowed value: 1023 */
startup_cwnd_gain:11, /* max allowed value: 2047 */
bw_probe_pif_gain:9, /* max allowed value: 511 */
usage_based_cwnd:1, /* boolean */
unused2:1;
u16 probe_rtt_win_ms:14, /* max allowed value: 16383 */
refill_add_inc:2; /* max allowed value: 3 */
u16 extra_acked_gain:11, /* max allowed value: 2047 */
extra_acked_win_rtts:5; /* max allowed value: 31*/
u16 pacing_gain[CYCLE_LEN]; /* max allowed value: 1023 */
/* Mostly BBR v2 parameters below here: */
u32 ecn_alpha_gain:8, /* max allowed value: 255 */
ecn_factor:8, /* max allowed value: 255 */
ecn_thresh:8, /* max allowed value: 255 */
beta:8; /* max allowed value: 255 */
u32 ecn_max_rtt_us:19, /* max allowed value: 524287 */
bw_probe_reno_gain:9, /* max allowed value: 511 */
full_loss_cnt:4; /* max allowed value: 15 */
u32 probe_rtt_cwnd_gain:8, /* max allowed value: 255 */
inflight_headroom:8, /* max allowed value: 255 */
loss_thresh:8, /* max allowed value: 255 */
bw_probe_max_rounds:8; /* max allowed value: 255 */
u32 bw_probe_rand_rounds:4, /* max allowed value: 15 */
bw_probe_base_us:26, /* usecs: 0..2^26-1 (67 secs) */
full_ecn_cnt:2; /* max allowed value: 3 */
u32 bw_probe_rand_us:26, /* usecs: 0..2^26-1 (67 secs) */
undo:1, /* boolean */
tso_rtt_shift:4, /* max allowed value: 15 */
unused5:1;
u32 ecn_reprobe_gain:9, /* max allowed value: 511 */
unused1:14,
ecn_alpha_init:9; /* max allowed value: 256 */
} params;
struct {
u32 snd_isn; /* Initial sequence number */
u32 rs_bw; /* last valid rate sample bw */
u32 target_cwnd; /* target cwnd, based on BDP */
u8 undo:1, /* Undo even happened but not yet logged */
unused:7;
char event; /* single-letter event debug codes */
u16 unused2;
} debug;
};
struct bbr_context {
u32 sample_bw;
u32 target_cwnd;
u32 log:1;
};
/* Window length of min_rtt filter (in sec). Max allowed value is 31 (0x1F) */
static u32 bbr_min_rtt_win_sec = 10;
/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode.
* Max allowed value is 511 (0x1FF).
*/
static u32 bbr_probe_rtt_mode_ms = 200;
/* Window length of probe_rtt_min_us filter (in ms), and consequently the
* typical interval between PROBE_RTT mode entries.
* Note that bbr_probe_rtt_win_ms must be <= bbr_min_rtt_win_sec * MSEC_PER_SEC
*/
static u32 bbr_probe_rtt_win_ms = 5000;
/* Skip TSO below the following bandwidth (bits/sec): */
static int bbr_min_tso_rate = 1200000;
/* Use min_rtt to help adapt TSO burst size, with smaller min_rtt resulting
* in bigger TSO bursts. By default we cut the RTT-based allowance in half
* for every 2^9 usec (aka 512 us) of RTT, so that the RTT-based allowance
* is below 1500 bytes after 6 * ~500 usec = 3ms.
*/
static u32 bbr_tso_rtt_shift = 9; /* halve allowance per 2^9 usecs, 512us */
/* Select cwnd TSO budget approach:
* 0: padding
* 1: flooring
*/
static uint bbr_cwnd_tso_budget = 1;
/* Pace at ~1% below estimated bw, on average, to reduce queue at bottleneck.
* In order to help drive the network toward lower queues and low latency while
* maintaining high utilization, the average pacing rate aims to be slightly
* lower than the estimated bandwidth. This is an important aspect of the
* design.
*/
static const int bbr_pacing_margin_percent = 1;
/* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain
* that will allow a smoothly increasing pacing rate that will double each RTT
* and send the same number of packets per RTT that an un-paced, slow-starting
* Reno or CUBIC flow would. Max allowed value is 2047 (0x7FF).
*/
static int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1;
/* The gain for deriving startup cwnd. Max allowed value is 2047 (0x7FF). */
static int bbr_startup_cwnd_gain = BBR_UNIT * 2885 / 1000 + 1;
/* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain
* the queue created in BBR_STARTUP in a single round. Max allowed value
* is 1023 (0x3FF).
*/
static int bbr_drain_gain = BBR_UNIT * 1000 / 2885;
/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs.
* Max allowed value is 2047 (0x7FF).
*/
static int bbr_cwnd_gain = BBR_UNIT * 2;
/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw.
* Max allowed value for each element is 1023 (0x3FF).
*/
enum bbr_pacing_gain_phase {
BBR_BW_PROBE_UP = 0, /* push up inflight to probe for bw/vol */
BBR_BW_PROBE_DOWN = 1, /* drain excess inflight from the queue */
BBR_BW_PROBE_CRUISE = 2, /* use pipe, w/ headroom in queue/pipe */
BBR_BW_PROBE_REFILL = 3, /* v2: refill the pipe again to 100% */
};
static int bbr_pacing_gain[] = {
BBR_UNIT * 5 / 4, /* probe for more available bw */
BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */
BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */
BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */
};
/* Try to keep at least this many packets in flight, if things go smoothly. For
* smooth functioning, a sliding window protocol ACKing every other packet
* needs at least 4 packets in flight. Max allowed value is 15 (0xF).
*/
static u32 bbr_cwnd_min_target = 4;
/* Cwnd to BDP proportion in PROBE_RTT mode scaled by BBR_UNIT. Default: 50%.
* Use 0 to disable. Max allowed value is 255.
*/
static u32 bbr_probe_rtt_cwnd_gain = BBR_UNIT * 1 / 2;
/* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */
/* If bw has increased significantly (1.25x), there may be more bw available.
* Max allowed value is 1023 (0x3FF).
*/
static u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4;
/* But after 3 rounds w/o significant bw growth, estimate pipe is full.
* Max allowed value is 7 (0x7).
*/
static u32 bbr_full_bw_cnt = 3;
static u32 bbr_flags; /* Debugging related stuff */
/* Whether to debug using printk.
*/
static bool bbr_debug_with_printk;
/* Whether to debug using ftrace event tcp:tcp_bbr_event.
* Ignored when bbr_debug_with_printk is set.
*/
static bool bbr_debug_ftrace;
/* Experiment: each cycle, try to hold sub-unity gain until inflight <= BDP. */
static bool bbr_drain_to_target = true; /* default: enabled */
/* Experiment: Flags to control BBR with ECN behavior.
*/
static bool bbr_precise_ece_ack = true; /* default: enabled */
/* The max rwin scaling shift factor is 14 (RFC 1323), so the max sane rwin is
* (2^(16+14) B)/(1024 B/packet) = 1M packets.
*/
static u32 bbr_cwnd_warn_val = 1U << 20;
static u16 bbr_debug_port_mask;
/* BBR module parameters. These are module parameters only in Google prod.
* Upstream these are intentionally not module parameters.
*/
static int bbr_pacing_gain_size = CYCLE_LEN;
/* Gain factor for adding extra_acked to target cwnd: */
static int bbr_extra_acked_gain = 256;
/* Window length of extra_acked window. Max allowed val is 31. */
static u32 bbr_extra_acked_win_rtts = 5;
/* Max allowed val for ack_epoch_acked, after which sampling epoch is reset */
static u32 bbr_ack_epoch_acked_reset_thresh = 1U << 20;
/* Time period for clamping cwnd increment due to ack aggregation */
static u32 bbr_extra_acked_max_us = 100 * 1000;
/* Use extra acked in startup ?
* 0: disabled
* 1: use latest extra_acked value from 1-2 rtt in startup
*/
static int bbr_extra_acked_in_startup = 1; /* default: enabled */
/* Experiment: don't grow cwnd beyond twice of what we just probed. */
static bool bbr_usage_based_cwnd; /* default: disabled */
/* For lab testing, researchers can enable BBRv2 ECN support with this flag,
* when they know that any ECN marks that the connections experience will be
* DCTCP/L4S-style ECN marks, rather than RFC3168 ECN marks.
* TODO(ncardwell): Production use of the BBRv2 ECN functionality depends on
* negotiation or configuration that is outside the scope of the BBRv2
* alpha release.
*/
static bool bbr_ecn_enable = false;
module_param_named(min_tso_rate, bbr_min_tso_rate, int, 0644);
module_param_named(tso_rtt_shift, bbr_tso_rtt_shift, int, 0644);
module_param_named(high_gain, bbr_high_gain, int, 0644);
module_param_named(drain_gain, bbr_drain_gain, int, 0644);
module_param_named(startup_cwnd_gain, bbr_startup_cwnd_gain, int, 0644);
module_param_named(cwnd_gain, bbr_cwnd_gain, int, 0644);
module_param_array_named(pacing_gain, bbr_pacing_gain, int,
&bbr_pacing_gain_size, 0644);
module_param_named(cwnd_min_target, bbr_cwnd_min_target, uint, 0644);
module_param_named(probe_rtt_cwnd_gain,
bbr_probe_rtt_cwnd_gain, uint, 0664);
module_param_named(cwnd_warn_val, bbr_cwnd_warn_val, uint, 0664);
module_param_named(debug_port_mask, bbr_debug_port_mask, ushort, 0644);
module_param_named(flags, bbr_flags, uint, 0644);
module_param_named(debug_ftrace, bbr_debug_ftrace, bool, 0644);
module_param_named(debug_with_printk, bbr_debug_with_printk, bool, 0644);
module_param_named(min_rtt_win_sec, bbr_min_rtt_win_sec, uint, 0644);
module_param_named(probe_rtt_mode_ms, bbr_probe_rtt_mode_ms, uint, 0644);
module_param_named(probe_rtt_win_ms, bbr_probe_rtt_win_ms, uint, 0644);
module_param_named(full_bw_thresh, bbr_full_bw_thresh, uint, 0644);
module_param_named(full_bw_cnt, bbr_full_bw_cnt, uint, 0644);
module_param_named(cwnd_tso_bduget, bbr_cwnd_tso_budget, uint, 0664);
module_param_named(extra_acked_gain, bbr_extra_acked_gain, int, 0664);
module_param_named(extra_acked_win_rtts,
bbr_extra_acked_win_rtts, uint, 0664);
module_param_named(extra_acked_max_us,
bbr_extra_acked_max_us, uint, 0664);
module_param_named(ack_epoch_acked_reset_thresh,
bbr_ack_epoch_acked_reset_thresh, uint, 0664);
module_param_named(drain_to_target, bbr_drain_to_target, bool, 0664);
module_param_named(precise_ece_ack, bbr_precise_ece_ack, bool, 0664);
module_param_named(extra_acked_in_startup,
bbr_extra_acked_in_startup, int, 0664);
module_param_named(usage_based_cwnd, bbr_usage_based_cwnd, bool, 0664);
module_param_named(ecn_enable, bbr_ecn_enable, bool, 0664);
static void bbr2_exit_probe_rtt(struct sock *sk);
static void bbr2_reset_congestion_signals(struct sock *sk);
static void bbr_check_probe_rtt_done(struct sock *sk);
/* Do we estimate that STARTUP filled the pipe? */
static bool bbr_full_bw_reached(const struct sock *sk)
{
const struct bbr *bbr = inet_csk_ca(sk);
return bbr->full_bw_reached;
}
/* Return the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */
static u32 bbr_max_bw(const struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return max(bbr->bw_hi[0], bbr->bw_hi[1]);
}
/* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */
static u32 bbr_bw(const struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return min(bbr_max_bw(sk), bbr->bw_lo);
}
/* Return maximum extra acked in past k-2k round trips,
* where k = bbr_extra_acked_win_rtts.
*/
static u16 bbr_extra_acked(const struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return max(bbr->extra_acked[0], bbr->extra_acked[1]);
}
/* Return rate in bytes per second, optionally with a gain.
* The order here is chosen carefully to avoid overflow of u64. This should
* work for input rates of up to 2.9Tbit/sec and gain of 2.89x.
*/
static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain,
int margin)
{
unsigned int mss = tcp_sk(sk)->mss_cache;
rate *= mss;
rate *= gain;
rate >>= BBR_SCALE;
rate *= USEC_PER_SEC / 100 * (100 - margin);
rate >>= BW_SCALE;
rate = max(rate, 1ULL);
return rate;
}
static u64 bbr_bw_bytes_per_sec(struct sock *sk, u64 rate)
{
return bbr_rate_bytes_per_sec(sk, rate, BBR_UNIT, 0);
}
static u64 bbr_rate_kbps(struct sock *sk, u64 rate)
{
rate = bbr_bw_bytes_per_sec(sk, rate);
rate *= 8;
do_div(rate, 1000);
return rate;
}
static u32 bbr_tso_segs_goal(struct sock *sk);
static void bbr_debug(struct sock *sk, u32 acked,
const struct rate_sample *rs, struct bbr_context *ctx)
{
static const char ca_states[] = {
[TCP_CA_Open] = 'O',
[TCP_CA_Disorder] = 'D',
[TCP_CA_CWR] = 'C',
[TCP_CA_Recovery] = 'R',
[TCP_CA_Loss] = 'L',
};
static const char mode[] = {
'G', /* Growing - BBR_STARTUP */
'D', /* Drain - BBR_DRAIN */
'W', /* Window - BBR_PROBE_BW */
'M', /* Min RTT - BBR_PROBE_RTT */
};
static const char ack_phase[] = { /* bbr_ack_phase strings */
'I', /* BBR_ACKS_INIT - 'Init' */
'R', /* BBR_ACKS_REFILLING - 'Refilling' */
'B', /* BBR_ACKS_PROBE_STARTING - 'Before' */
'F', /* BBR_ACKS_PROBE_FEEDBACK - 'Feedback' */
'A', /* BBR_ACKS_PROBE_STOPPING - 'After' */
};
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
const u32 una = tp->snd_una - bbr->debug.snd_isn;
const u32 fack = tcp_highest_sack_seq(tp);
const u16 dport = ntohs(inet_sk(sk)->inet_dport);
bool is_port_match = (bbr_debug_port_mask &&
((dport & bbr_debug_port_mask) == 0));
char debugmsg[320];
if (sk->sk_state == TCP_SYN_SENT)
return; /* no bbr_init() yet if SYN retransmit -> CA_Loss */
if (!tp->snd_cwnd || tp->snd_cwnd > bbr_cwnd_warn_val) {
char addr[INET6_ADDRSTRLEN + 10] = { 0 };
if (sk->sk_family == AF_INET)
snprintf(addr, sizeof(addr), "%pI4:%u",
&inet_sk(sk)->inet_daddr, dport);
else if (sk->sk_family == AF_INET6)
snprintf(addr, sizeof(addr), "%pI6:%u",
&sk->sk_v6_daddr, dport);
WARN_ONCE(1,
"BBR %s cwnd alert: %u "
"snd_una: %u ca: %d pacing_gain: %u cwnd_gain: %u "
"bw: %u rtt: %u min_rtt: %u "
"acked: %u tso_segs: %u "
"bw: %d %ld %d pif: %u\n",
addr, tp->snd_cwnd,
una, inet_csk(sk)->icsk_ca_state,
bbr->pacing_gain, bbr->cwnd_gain,
bbr_max_bw(sk), (tp->srtt_us >> 3), bbr->min_rtt_us,
acked, bbr_tso_segs_goal(sk),
rs->delivered, rs->interval_us, rs->is_retrans,
tcp_packets_in_flight(tp));
}
if (likely(!bbr_debug_with_printk && !bbr_debug_ftrace))
return;
if (!sock_flag(sk, SOCK_DBG) && !is_port_match)
return;
if (!ctx->log && !tp->app_limited && !(bbr_flags & FLAG_DEBUG_VERBOSE))
return;
if (ipv4_is_loopback(inet_sk(sk)->inet_daddr) &&
!(bbr_flags & FLAG_DEBUG_LOOPBACK))
return;
snprintf(debugmsg, sizeof(debugmsg) - 1,
"BBR %pI4:%-5u %5u,%03u:%-7u %c "
"%c %2u br %2u cr %2d rtt %5ld d %2d i %5ld mrtt %d %cbw %llu "
"bw %llu lb %llu ib %llu qb %llu "
"a %u if %2u %c %c dl %u l %u al %u # %u t %u %c %c "
"lr %d er %d ea %d bwl %lld il %d ih %d c %d "
"v %d %c %u %c %s\n",
&inet_sk(sk)->inet_daddr, dport,
una / 1000, una % 1000, fack - tp->snd_una,
ca_states[inet_csk(sk)->icsk_ca_state],
bbr->debug.undo ? '@' : mode[bbr->mode],
tp->snd_cwnd,
bbr_extra_acked(sk), /* br (legacy): extra_acked */
rs->tx_in_flight, /* cr (legacy): tx_inflight */
rs->rtt_us,
rs->delivered,
rs->interval_us,
bbr->min_rtt_us,
rs->is_app_limited ? '_' : 'l',
bbr_rate_kbps(sk, ctx->sample_bw), /* lbw: latest sample bw */
bbr_rate_kbps(sk, bbr_max_bw(sk)), /* bw: max bw */
0ULL, /* lb: [obsolete] */
0ULL, /* ib: [obsolete] */
div_u64((u64)sk->sk_pacing_rate * 8, 1000),
acked,
tcp_packets_in_flight(tp),
rs->is_ack_delayed ? 'd' : '.',
bbr->round_start ? '*' : '.',
tp->delivered, tp->lost,
tp->app_limited,
0, /* #: [obsolete] */
ctx->target_cwnd,
tp->reord_seen ? 'r' : '.', /* r: reordering seen? */
ca_states[bbr->prev_ca_state],
(rs->lost + rs->delivered) > 0 ?
(1000 * rs->lost /
(rs->lost + rs->delivered)) : 0, /* lr: loss rate x1000 */
(rs->delivered) > 0 ?
(1000 * rs->delivered_ce /
(rs->delivered)) : 0, /* er: ECN rate x1000 */
1000 * bbr->ecn_alpha >> BBR_SCALE, /* ea: ECN alpha x1000 */
bbr->bw_lo == ~0U ?
-1 : (s64)bbr_rate_kbps(sk, bbr->bw_lo), /* bwl */
bbr->inflight_lo, /* il */
bbr->inflight_hi, /* ih */
bbr->bw_probe_up_cnt, /* c */
2, /* v: version */
bbr->debug.event,
bbr->cycle_idx,
ack_phase[bbr->ack_phase],
bbr->bw_probe_samples ? "Y" : "N");
debugmsg[sizeof(debugmsg) - 1] = 0;
/* printk takes a higher precedence. */
if (bbr_debug_with_printk)
printk(KERN_DEBUG "%s", debugmsg);
if (unlikely(bbr->debug.undo))
bbr->debug.undo = 0;
}
/* Convert a BBR bw and gain factor to a pacing rate in bytes per second. */
static unsigned long bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)
{
u64 rate = bw;
rate = bbr_rate_bytes_per_sec(sk, rate, gain,
bbr_pacing_margin_percent);
rate = min_t(u64, rate, sk->sk_max_pacing_rate);
return rate;
}
/* Initialize pacing rate to: high_gain * init_cwnd / RTT. */
static void bbr_init_pacing_rate_from_rtt(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u64 bw;
u32 rtt_us;
if (tp->srtt_us) { /* any RTT sample yet? */
rtt_us = max(tp->srtt_us >> 3, 1U);
bbr->has_seen_rtt = 1;
} else { /* no RTT sample yet */
rtt_us = USEC_PER_MSEC; /* use nominal default RTT */
}
bw = (u64)tp->snd_cwnd * BW_UNIT;
do_div(bw, rtt_us);
sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr->params.high_gain);
}
/* Pace using current bw estimate and a gain factor. */
static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
unsigned long rate = bbr_bw_to_pacing_rate(sk, bw, gain);
if (unlikely(!bbr->has_seen_rtt && tp->srtt_us))
bbr_init_pacing_rate_from_rtt(sk);
if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate)
sk->sk_pacing_rate = rate;
}
static u32 bbr_min_tso_segs(struct sock *sk)
{
return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
}
/* Return the number of segments BBR would like in a TSO/GSO skb, given
* a particular max gso size as a constraint.
*/
static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now,
u32 gso_max_size)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 segs, r;
u64 bytes;
/* Budget a TSO/GSO burst size allowance based on bw (pacing_rate). */
bytes = sk->sk_pacing_rate >> sk->sk_pacing_shift;
/* Budget a TSO/GSO burst size allowance based on min_rtt. For every
* K = 2^tso_rtt_shift microseconds of min_rtt, halve the burst.
* The min_rtt-based burst allowance is: 64 KBytes / 2^(min_rtt/K)
*/
if (bbr->params.tso_rtt_shift) {
r = bbr->min_rtt_us >> bbr->params.tso_rtt_shift;
if (r < BITS_PER_TYPE(u32)) /* prevent undefined behavior */
bytes += GSO_MAX_SIZE >> r;
}
bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
segs = max_t(u32, div_u64(bytes, mss_now), bbr_min_tso_segs(sk));
return segs;
}
/* Custom tcp_tso_autosize() for BBR, used at transmit time to cap skb size. */
static u32 bbr_tso_segs(struct sock *sk, unsigned int mss_now)
{
return bbr_tso_segs_generic(sk, mss_now, sk->sk_gso_max_size);
}
/* Like bbr_tso_segs(), using mss_cache, ignoring driver's sk_gso_max_size. */
static u32 bbr_tso_segs_goal(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
return bbr_tso_segs_generic(sk, tp->mss_cache, GSO_MAX_SIZE);
}
/* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
static void bbr_save_cwnd(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT)
bbr->prior_cwnd = tp->snd_cwnd; /* this cwnd is good enough */
else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */
bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd);
}
static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (event == CA_EVENT_TX_START && tp->app_limited) {
bbr->idle_restart = 1;
bbr->ack_epoch_mstamp = tp->tcp_mstamp;
bbr->ack_epoch_acked = 0;
/* Avoid pointless buffer overflows: pace at est. bw if we don't
* need more speed (we're restarting from idle and app-limited).
*/
if (bbr->mode == BBR_PROBE_BW)
bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT);
else if (bbr->mode == BBR_PROBE_RTT)
bbr_check_probe_rtt_done(sk);
} else if ((event == CA_EVENT_ECN_IS_CE ||
event == CA_EVENT_ECN_NO_CE) &&
bbr_ecn_enable &&
bbr->params.precise_ece_ack) {
u32 state = bbr->ce_state;
dctcp_ece_ack_update(sk, event, &bbr->prior_rcv_nxt, &state);
bbr->ce_state = state;
if (tp->fast_ack_mode == 2 && event == CA_EVENT_ECN_IS_CE)
tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
}
}
/* Calculate bdp based on min RTT and the estimated bottleneck bandwidth:
*
* bdp = ceil(bw * min_rtt * gain)
*
* The key factor, gain, controls the amount of queue. While a small gain
* builds a smaller queue, it becomes more vulnerable to noise in RTT
* measurements (e.g., delayed ACKs or other ACK compression effects). This
* noise may cause BBR to under-estimate the rate.
*/
static u32 bbr_bdp(struct sock *sk, u32 bw, int gain)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 bdp;
u64 w;
/* If we've never had a valid RTT sample, cap cwnd at the initial
* default. This should only happen when the connection is not using TCP
* timestamps and has retransmitted all of the SYN/SYNACK/data packets
* ACKed so far. In this case, an RTO can cut cwnd to 1, in which
* case we need to slow-start up toward something safe: initial cwnd.
*/
if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */
return bbr->init_cwnd; /* be safe: cap at initial cwnd */
w = (u64)bw * bbr->min_rtt_us;
/* Apply a gain to the given value, remove the BW_SCALE shift, and
* round the value up to avoid a negative feedback loop.
*/
bdp = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT;
return bdp;
}
/* To achieve full performance in high-speed paths, we budget enough cwnd to
* fit full-sized skbs in-flight on both end hosts to fully utilize the path:
* - one skb in sending host Qdisc,
* - one skb in sending host TSO/GSO engine
* - one skb being received by receiver host LRO/GRO/delayed-ACK engine
* Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because
* in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets,
* which allows 2 outstanding 2-packet sequences, to try to keep pipe
* full even with ACK-every-other-packet delayed ACKs.
*/
static u32 bbr_quantization_budget(struct sock *sk, u32 cwnd)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 tso_segs_goal;
tso_segs_goal = 3 * bbr_tso_segs_goal(sk);
/* Allow enough full-sized skbs in flight to utilize end systems. */
if (bbr->params.cwnd_tso_budget == 1) {
cwnd = max_t(u32, cwnd, tso_segs_goal);
cwnd = max_t(u32, cwnd, bbr->params.cwnd_min_target);
} else {
cwnd += tso_segs_goal;
cwnd = (cwnd + 1) & ~1U;
}
/* Ensure gain cycling gets inflight above BDP even for small BDPs. */
if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == BBR_BW_PROBE_UP)
cwnd += 2;
return cwnd;
}
/* Find inflight based on min RTT and the estimated bottleneck bandwidth. */
static u32 bbr_inflight(struct sock *sk, u32 bw, int gain)
{
u32 inflight;
inflight = bbr_bdp(sk, bw, gain);
inflight = bbr_quantization_budget(sk, inflight);
return inflight;
}
/* With pacing at lower layers, there's often less data "in the network" than
* "in flight". With TSQ and departure time pacing at lower layers (e.g. fq),
* we often have several skbs queued in the pacing layer with a pre-scheduled
* earliest departure time (EDT). BBR adapts its pacing rate based on the
* inflight level that it estimates has already been "baked in" by previous
* departure time decisions. We calculate a rough estimate of the number of our
* packets that might be in the network at the earliest departure time for the
* next skb scheduled:
* in_network_at_edt = inflight_at_edt - (EDT - now) * bw
* If we're increasing inflight, then we want to know if the transmit of the
* EDT skb will push inflight above the target, so inflight_at_edt includes
* bbr_tso_segs_goal() from the skb departing at EDT. If decreasing inflight,
* then estimate if inflight will sink too low just before the EDT transmit.
*/
static u32 bbr_packets_in_net_at_edt(struct sock *sk, u32 inflight_now)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u64 now_ns, edt_ns, interval_us;
u32 interval_delivered, inflight_at_edt;
now_ns = tp->tcp_clock_cache;
edt_ns = max(tp->tcp_wstamp_ns, now_ns);
interval_us = div_u64(edt_ns - now_ns, NSEC_PER_USEC);
interval_delivered = (u64)bbr_bw(sk) * interval_us >> BW_SCALE;
inflight_at_edt = inflight_now;
if (bbr->pacing_gain > BBR_UNIT) /* increasing inflight */
inflight_at_edt += bbr_tso_segs_goal(sk); /* include EDT skb */
if (interval_delivered >= inflight_at_edt)
return 0;
return inflight_at_edt - interval_delivered;
}
/* Find the cwnd increment based on estimate of ack aggregation */
static u32 bbr_ack_aggregation_cwnd(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 max_aggr_cwnd, aggr_cwnd = 0;
if (bbr->params.extra_acked_gain &&
(bbr_full_bw_reached(sk) || bbr->params.extra_acked_in_startup)) {
max_aggr_cwnd = ((u64)bbr_bw(sk) * bbr_extra_acked_max_us)
/ BW_UNIT;
aggr_cwnd = (bbr->params.extra_acked_gain * bbr_extra_acked(sk))
>> BBR_SCALE;
aggr_cwnd = min(aggr_cwnd, max_aggr_cwnd);
}
return aggr_cwnd;
}
/* Returns the cwnd for PROBE_RTT mode. */
static u32 bbr_probe_rtt_cwnd(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->params.probe_rtt_cwnd_gain == 0)
return bbr->params.cwnd_min_target;
return max_t(u32, bbr->params.cwnd_min_target,
bbr_bdp(sk, bbr_bw(sk), bbr->params.probe_rtt_cwnd_gain));
}
/* Slow-start up toward target cwnd (if bw estimate is growing, or packet loss
* has drawn us down below target), or snap down to target if we're above it.
*/
static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs,
u32 acked, u32 bw, int gain, u32 cwnd,
struct bbr_context *ctx)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 target_cwnd = 0, prev_cwnd = tp->snd_cwnd, max_probe;
if (!acked)
goto done; /* no packet fully ACKed; just apply caps */
target_cwnd = bbr_bdp(sk, bw, gain);
/* Increment the cwnd to account for excess ACKed data that seems
* due to aggregation (of data and/or ACKs) visible in the ACK stream.
*/
target_cwnd += bbr_ack_aggregation_cwnd(sk);
target_cwnd = bbr_quantization_budget(sk, target_cwnd);
/* If we're below target cwnd, slow start cwnd toward target cwnd. */
bbr->debug.target_cwnd = target_cwnd;
/* Update cwnd and enable fast path if cwnd reaches target_cwnd. */
bbr->try_fast_path = 0;
if (bbr_full_bw_reached(sk)) { /* only cut cwnd if we filled the pipe */
cwnd += acked;
if (cwnd >= target_cwnd) {
cwnd = target_cwnd;
bbr->try_fast_path = 1;
}
} else if (cwnd < target_cwnd || cwnd < 2 * bbr->init_cwnd) {
cwnd += acked;
} else {
bbr->try_fast_path = 1;
}
/* When growing cwnd, don't grow beyond twice what we just probed. */
if (bbr->params.usage_based_cwnd) {
max_probe = max(2 * tp->max_packets_out, tp->snd_cwnd);
cwnd = min(cwnd, max_probe);
}
cwnd = max_t(u32, cwnd, bbr->params.cwnd_min_target);
done:
tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); /* apply global cap */
if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */
tp->snd_cwnd = min_t(u32, tp->snd_cwnd, bbr_probe_rtt_cwnd(sk));
ctx->target_cwnd = target_cwnd;
ctx->log = (tp->snd_cwnd != prev_cwnd);
}
/* See if we have reached next round trip */
static void bbr_update_round_start(struct sock *sk,
const struct rate_sample *rs, struct bbr_context *ctx)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr->round_start = 0;
/* See if we've reached the next RTT */
if (rs->interval_us > 0 &&
!before(rs->prior_delivered, bbr->next_rtt_delivered)) {
bbr->next_rtt_delivered = tp->delivered;
bbr->round_start = 1;
}
}
/* Calculate the bandwidth based on how fast packets are delivered */
static void bbr_calculate_bw_sample(struct sock *sk,
const struct rate_sample *rs, struct bbr_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
u64 bw = 0;
/* Divide delivered by the interval to find a (lower bound) bottleneck
* bandwidth sample. Delivered is in packets and interval_us in uS and
* ratio will be <<1 for most connections. So delivered is first scaled.
* Round up to allow growth at low rates, even with integer division.
*/
if (rs->interval_us > 0) {
if (WARN_ONCE(rs->delivered < 0,
"negative delivered: %d interval_us: %ld\n",
rs->delivered, rs->interval_us))
return;
bw = DIV_ROUND_UP_ULL((u64)rs->delivered * BW_UNIT, rs->interval_us);
}
ctx->sample_bw = bw;
bbr->debug.rs_bw = bw;
}
/* Estimates the windowed max degree of ack aggregation.
* This is used to provision extra in-flight data to keep sending during
* inter-ACK silences.
*
* Degree of ack aggregation is estimated as extra data acked beyond expected.
*
* max_extra_acked = "maximum recent excess data ACKed beyond max_bw * interval"
* cwnd += max_extra_acked
*
* Max extra_acked is clamped by cwnd and bw * bbr_extra_acked_max_us (100 ms).
* Max filter is an approximate sliding window of 5-10 (packet timed) round
* trips for non-startup phase, and 1-2 round trips for startup.
*/
static void bbr_update_ack_aggregation(struct sock *sk,
const struct rate_sample *rs)
{
u32 epoch_us, expected_acked, extra_acked;
struct bbr *bbr = inet_csk_ca(sk);
struct tcp_sock *tp = tcp_sk(sk);
u32 extra_acked_win_rtts_thresh = bbr->params.extra_acked_win_rtts;
if (!bbr->params.extra_acked_gain || rs->acked_sacked <= 0 ||
rs->delivered < 0 || rs->interval_us <= 0)
return;
if (bbr->round_start) {
bbr->extra_acked_win_rtts = min(0x1F,
bbr->extra_acked_win_rtts + 1);
if (bbr->params.extra_acked_in_startup &&
!bbr_full_bw_reached(sk))
extra_acked_win_rtts_thresh = 1;
if (bbr->extra_acked_win_rtts >=
extra_acked_win_rtts_thresh) {
bbr->extra_acked_win_rtts = 0;
bbr->extra_acked_win_idx = bbr->extra_acked_win_idx ?
0 : 1;
bbr->extra_acked[bbr->extra_acked_win_idx] = 0;
}
}
/* Compute how many packets we expected to be delivered over epoch. */
epoch_us = tcp_stamp_us_delta(tp->delivered_mstamp,
bbr->ack_epoch_mstamp);
expected_acked = ((u64)bbr_bw(sk) * epoch_us) / BW_UNIT;
/* Reset the aggregation epoch if ACK rate is below expected rate or
* significantly large no. of ack received since epoch (potentially
* quite old epoch).
*/
if (bbr->ack_epoch_acked <= expected_acked ||
(bbr->ack_epoch_acked + rs->acked_sacked >=
bbr_ack_epoch_acked_reset_thresh)) {
bbr->ack_epoch_acked = 0;
bbr->ack_epoch_mstamp = tp->delivered_mstamp;
expected_acked = 0;
}
/* Compute excess data delivered, beyond what was expected. */
bbr->ack_epoch_acked = min_t(u32, 0xFFFFF,
bbr->ack_epoch_acked + rs->acked_sacked);
extra_acked = bbr->ack_epoch_acked - expected_acked;
extra_acked = min(extra_acked, tp->snd_cwnd);
if (extra_acked > bbr->extra_acked[bbr->extra_acked_win_idx])
bbr->extra_acked[bbr->extra_acked_win_idx] = extra_acked;
}
/* Estimate when the pipe is full, using the change in delivery rate: BBR
* estimates that STARTUP filled the pipe if the estimated bw hasn't changed by
* at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) non-app-limited
* rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill the
* higher rwin, 3: we get higher delivery rate samples. Or transient
* cross-traffic or radio noise can go away. CUBIC Hystart shares a similar
* design goal, but uses delay and inter-ACK spacing instead of bandwidth.
*/
static void bbr_check_full_bw_reached(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 bw_thresh;
if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited)
return;
bw_thresh = (u64)bbr->full_bw * bbr->params.full_bw_thresh >> BBR_SCALE;
if (bbr_max_bw(sk) >= bw_thresh) {
bbr->full_bw = bbr_max_bw(sk);
bbr->full_bw_cnt = 0;
return;
}
++bbr->full_bw_cnt;
bbr->full_bw_reached = bbr->full_bw_cnt >= bbr->params.full_bw_cnt;
}
/* If pipe is probably full, drain the queue and then enter steady-state. */
static bool bbr_check_drain(struct sock *sk, const struct rate_sample *rs,
struct bbr_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) {
bbr->mode = BBR_DRAIN; /* drain queue we created */
tcp_sk(sk)->snd_ssthresh =
bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT);
bbr2_reset_congestion_signals(sk);
} /* fall through to check if in-flight is already small: */
if (bbr->mode == BBR_DRAIN &&
bbr_packets_in_net_at_edt(sk, tcp_packets_in_flight(tcp_sk(sk))) <=
bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT))
return true; /* exiting DRAIN now */
return false;
}
static void bbr_check_probe_rtt_done(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (!(bbr->probe_rtt_done_stamp &&
after(tcp_jiffies32, bbr->probe_rtt_done_stamp)))
return;
bbr->probe_rtt_min_stamp = tcp_jiffies32; /* schedule next PROBE_RTT */
tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd);
bbr2_exit_probe_rtt(sk);
}
/* The goal of PROBE_RTT mode is to have BBR flows cooperatively and
* periodically drain the bottleneck queue, to converge to measure the true
* min_rtt (unloaded propagation delay). This allows the flows to keep queues
* small (reducing queuing delay and packet loss) and achieve fairness among
* BBR flows.
*
* The min_rtt filter window is 10 seconds. When the min_rtt estimate expires,
* we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 packets.
* After at least bbr_probe_rtt_mode_ms=200ms and at least one packet-timed
* round trip elapsed with that flight size <= 4, we leave PROBE_RTT mode and
* re-enter the previous mode. BBR uses 200ms to approximately bound the
* performance penalty of PROBE_RTT's cwnd capping to roughly 2% (200ms/10s).
*
* Note that flows need only pay 2% if they are busy sending over the last 10
* seconds. Interactive applications (e.g., Web, RPCs, video chunks) often have
* natural silences or low-rate periods within 10 seconds where the rate is low
* enough for long enough to drain its queue in the bottleneck. We pick up
* these min RTT measurements opportunistically with our min_rtt filter. :-)
*/
static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bool probe_rtt_expired, min_rtt_expired;
u32 expire;
/* Track min RTT in probe_rtt_win_ms to time next PROBE_RTT state. */
expire = bbr->probe_rtt_min_stamp +
msecs_to_jiffies(bbr->params.probe_rtt_win_ms);
probe_rtt_expired = after(tcp_jiffies32, expire);
if (rs->rtt_us >= 0 &&
(rs->rtt_us <= bbr->probe_rtt_min_us ||
(probe_rtt_expired && !rs->is_ack_delayed))) {
bbr->probe_rtt_min_us = rs->rtt_us;
bbr->probe_rtt_min_stamp = tcp_jiffies32;
}
/* Track min RTT seen in the min_rtt_win_sec filter window: */
expire = bbr->min_rtt_stamp + bbr->params.min_rtt_win_sec * HZ;
min_rtt_expired = after(tcp_jiffies32, expire);
if (bbr->probe_rtt_min_us <= bbr->min_rtt_us ||
min_rtt_expired) {
bbr->min_rtt_us = bbr->probe_rtt_min_us;
bbr->min_rtt_stamp = bbr->probe_rtt_min_stamp;
}
if (bbr->params.probe_rtt_mode_ms > 0 && probe_rtt_expired &&
!bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) {
bbr->mode = BBR_PROBE_RTT; /* dip, drain queue */
bbr_save_cwnd(sk); /* note cwnd so we can restore it */
bbr->probe_rtt_done_stamp = 0;
bbr->ack_phase = BBR_ACKS_PROBE_STOPPING;
bbr->next_rtt_delivered = tp->delivered;
}
if (bbr->mode == BBR_PROBE_RTT) {
/* Ignore low rate samples during this mode. */
tp->app_limited =
(tp->delivered + tcp_packets_in_flight(tp)) ? : 1;
/* Maintain min packets in flight for max(200 ms, 1 round). */
if (!bbr->probe_rtt_done_stamp &&
tcp_packets_in_flight(tp) <= bbr_probe_rtt_cwnd(sk)) {
bbr->probe_rtt_done_stamp = tcp_jiffies32 +
msecs_to_jiffies(bbr->params.probe_rtt_mode_ms);
bbr->probe_rtt_round_done = 0;
bbr->next_rtt_delivered = tp->delivered;
} else if (bbr->probe_rtt_done_stamp) {
if (bbr->round_start)
bbr->probe_rtt_round_done = 1;
if (bbr->probe_rtt_round_done)
bbr_check_probe_rtt_done(sk);
}
}
/* Restart after idle ends only once we process a new S/ACK for data */
if (rs->delivered > 0)
bbr->idle_restart = 0;
}
static void bbr_update_gains(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
switch (bbr->mode) {
case BBR_STARTUP:
bbr->pacing_gain = bbr->params.high_gain;
bbr->cwnd_gain = bbr->params.startup_cwnd_gain;
break;
case BBR_DRAIN:
bbr->pacing_gain = bbr->params.drain_gain; /* slow, to drain */
bbr->cwnd_gain = bbr->params.startup_cwnd_gain; /* keep cwnd */
break;
case BBR_PROBE_BW:
bbr->pacing_gain = bbr->params.pacing_gain[bbr->cycle_idx];
bbr->cwnd_gain = bbr->params.cwnd_gain;
break;
case BBR_PROBE_RTT:
bbr->pacing_gain = BBR_UNIT;
bbr->cwnd_gain = BBR_UNIT;
break;
default:
WARN_ONCE(1, "BBR bad mode: %u\n", bbr->mode);
break;
}
}
static void bbr_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
int i;
WARN_ON_ONCE(tp->snd_cwnd >= bbr_cwnd_warn_val);
bbr->initialized = 1;
bbr->params.high_gain = min(0x7FF, bbr_high_gain);
bbr->params.drain_gain = min(0x3FF, bbr_drain_gain);
bbr->params.startup_cwnd_gain = min(0x7FF, bbr_startup_cwnd_gain);
bbr->params.cwnd_gain = min(0x7FF, bbr_cwnd_gain);
bbr->params.cwnd_tso_budget = min(0x1U, bbr_cwnd_tso_budget);
bbr->params.cwnd_min_target = min(0xFU, bbr_cwnd_min_target);
bbr->params.min_rtt_win_sec = min(0x1FU, bbr_min_rtt_win_sec);
bbr->params.probe_rtt_mode_ms = min(0x1FFU, bbr_probe_rtt_mode_ms);
bbr->params.full_bw_cnt = min(0x7U, bbr_full_bw_cnt);
bbr->params.full_bw_thresh = min(0x3FFU, bbr_full_bw_thresh);
bbr->params.extra_acked_gain = min(0x7FF, bbr_extra_acked_gain);
bbr->params.extra_acked_win_rtts = min(0x1FU, bbr_extra_acked_win_rtts);
bbr->params.drain_to_target = bbr_drain_to_target ? 1 : 0;
bbr->params.precise_ece_ack = bbr_precise_ece_ack ? 1 : 0;
bbr->params.extra_acked_in_startup = bbr_extra_acked_in_startup ? 1 : 0;
bbr->params.probe_rtt_cwnd_gain = min(0xFFU, bbr_probe_rtt_cwnd_gain);
bbr->params.probe_rtt_win_ms =
min(0x3FFFU,
min_t(u32, bbr_probe_rtt_win_ms,
bbr->params.min_rtt_win_sec * MSEC_PER_SEC));
for (i = 0; i < CYCLE_LEN; i++)
bbr->params.pacing_gain[i] = min(0x3FF, bbr_pacing_gain[i]);
bbr->params.usage_based_cwnd = bbr_usage_based_cwnd ? 1 : 0;
bbr->params.tso_rtt_shift = min(0xFU, bbr_tso_rtt_shift);
bbr->debug.snd_isn = tp->snd_una;
bbr->debug.target_cwnd = 0;
bbr->debug.undo = 0;
bbr->init_cwnd = min(0x7FU, tp->snd_cwnd);
bbr->prior_cwnd = tp->prior_cwnd;
tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
bbr->next_rtt_delivered = 0;
bbr->prev_ca_state = TCP_CA_Open;
bbr->packet_conservation = 0;
bbr->probe_rtt_done_stamp = 0;
bbr->probe_rtt_round_done = 0;
bbr->probe_rtt_min_us = tcp_min_rtt(tp);
bbr->probe_rtt_min_stamp = tcp_jiffies32;
bbr->min_rtt_us = tcp_min_rtt(tp);
bbr->min_rtt_stamp = tcp_jiffies32;
bbr->has_seen_rtt = 0;
bbr_init_pacing_rate_from_rtt(sk);
bbr->round_start = 0;
bbr->idle_restart = 0;
bbr->full_bw_reached = 0;
bbr->full_bw = 0;
bbr->full_bw_cnt = 0;
bbr->cycle_mstamp = 0;
bbr->cycle_idx = 0;
bbr->mode = BBR_STARTUP;
bbr->debug.rs_bw = 0;
bbr->ack_epoch_mstamp = tp->tcp_mstamp;
bbr->ack_epoch_acked = 0;
bbr->extra_acked_win_rtts = 0;
bbr->extra_acked_win_idx = 0;
bbr->extra_acked[0] = 0;
bbr->extra_acked[1] = 0;
bbr->ce_state = 0;
bbr->prior_rcv_nxt = tp->rcv_nxt;
bbr->try_fast_path = 0;
cmpxchg(&sk->sk_pacing_status, SK_PACING_NONE, SK_PACING_NEEDED);
}
static u32 bbr_sndbuf_expand(struct sock *sk)
{
/* Provision 3 * cwnd since BBR may slow-start even during recovery. */
return 3;
}
/* __________________________________________________________________________
*
* Functions new to BBR v2 ("bbr") congestion control are below here.
* __________________________________________________________________________
*/
/* Incorporate a new bw sample into the current window of our max filter. */
static void bbr2_take_bw_hi_sample(struct sock *sk, u32 bw)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->bw_hi[1] = max(bw, bbr->bw_hi[1]);
}
/* Keep max of last 1-2 cycles. Each PROBE_BW cycle, flip filter window. */
static void bbr2_advance_bw_hi_filter(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
if (!bbr->bw_hi[1])
return; /* no samples in this window; remember old window */
bbr->bw_hi[0] = bbr->bw_hi[1];
bbr->bw_hi[1] = 0;
}
/* How much do we want in flight? Our BDP, unless congestion cut cwnd. */
static u32 bbr2_target_inflight(struct sock *sk)
{
u32 bdp = bbr_inflight(sk, bbr_bw(sk), BBR_UNIT);
return min(bdp, tcp_sk(sk)->snd_cwnd);
}
static bool bbr2_is_probing_bandwidth(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return (bbr->mode == BBR_STARTUP) ||
(bbr->mode == BBR_PROBE_BW &&
(bbr->cycle_idx == BBR_BW_PROBE_REFILL ||
bbr->cycle_idx == BBR_BW_PROBE_UP));
}
/* Has the given amount of time elapsed since we marked the phase start? */
static bool bbr2_has_elapsed_in_phase(const struct sock *sk, u32 interval_us)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct bbr *bbr = inet_csk_ca(sk);
return tcp_stamp_us_delta(tp->tcp_mstamp,
bbr->cycle_mstamp + interval_us) > 0;
}
static void bbr2_handle_queue_too_high_in_startup(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->full_bw_reached = 1;
bbr->inflight_hi = bbr_inflight(sk, bbr_max_bw(sk), BBR_UNIT);
}
/* Exit STARTUP upon N consecutive rounds with ECN mark rate > ecn_thresh. */
static void bbr2_check_ecn_too_high_in_startup(struct sock *sk, u32 ce_ratio)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr_full_bw_reached(sk) || !bbr->ecn_eligible ||
!bbr->params.full_ecn_cnt || !bbr->params.ecn_thresh)
return;
if (ce_ratio >= bbr->params.ecn_thresh)
bbr->startup_ecn_rounds++;
else
bbr->startup_ecn_rounds = 0;
if (bbr->startup_ecn_rounds >= bbr->params.full_ecn_cnt) {
bbr->debug.event = 'E'; /* ECN caused STARTUP exit */
bbr2_handle_queue_too_high_in_startup(sk);
return;
}
}
static void bbr2_update_ecn_alpha(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
s32 delivered, delivered_ce;
u64 alpha, ce_ratio;
u32 gain;
if (bbr->params.ecn_factor == 0)
return;
delivered = tp->delivered - bbr->alpha_last_delivered;
delivered_ce = tp->delivered_ce - bbr->alpha_last_delivered_ce;
if (delivered == 0 || /* avoid divide by zero */
WARN_ON_ONCE(delivered < 0 || delivered_ce < 0)) /* backwards? */
return;
/* See if we should use ECN sender logic for this connection. */
if (!bbr->ecn_eligible && bbr_ecn_enable &&
(bbr->min_rtt_us <= bbr->params.ecn_max_rtt_us ||
!bbr->params.ecn_max_rtt_us))
bbr->ecn_eligible = 1;
ce_ratio = (u64)delivered_ce << BBR_SCALE;
do_div(ce_ratio, delivered);
gain = bbr->params.ecn_alpha_gain;
alpha = ((BBR_UNIT - gain) * bbr->ecn_alpha) >> BBR_SCALE;
alpha += (gain * ce_ratio) >> BBR_SCALE;
bbr->ecn_alpha = min_t(u32, alpha, BBR_UNIT);
bbr->alpha_last_delivered = tp->delivered;
bbr->alpha_last_delivered_ce = tp->delivered_ce;
bbr2_check_ecn_too_high_in_startup(sk, ce_ratio);
}
/* Each round trip of BBR_BW_PROBE_UP, double volume of probing data. */
static void bbr2_raise_inflight_hi_slope(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 growth_this_round, cnt;
/* Calculate "slope": packets S/Acked per inflight_hi increment. */
growth_this_round = 1 << bbr->bw_probe_up_rounds;
bbr->bw_probe_up_rounds = min(bbr->bw_probe_up_rounds + 1, 30);
cnt = tp->snd_cwnd / growth_this_round;
cnt = max(cnt, 1U);
bbr->bw_probe_up_cnt = cnt;
bbr->debug.event = 'G'; /* Grow inflight_hi slope */
}
/* In BBR_BW_PROBE_UP, not seeing high loss/ECN/queue, so raise inflight_hi. */
static void bbr2_probe_inflight_hi_upward(struct sock *sk,
const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 delta;
if (!tp->is_cwnd_limited || tp->snd_cwnd < bbr->inflight_hi) {
bbr->bw_probe_up_acks = 0; /* don't accmulate unused credits */
return; /* not fully using inflight_hi, so don't grow it */
}
/* For each bw_probe_up_cnt packets ACKed, increase inflight_hi by 1. */
bbr->bw_probe_up_acks += rs->acked_sacked;
if (bbr->bw_probe_up_acks >= bbr->bw_probe_up_cnt) {
delta = bbr->bw_probe_up_acks / bbr->bw_probe_up_cnt;
bbr->bw_probe_up_acks -= delta * bbr->bw_probe_up_cnt;
bbr->inflight_hi += delta;
bbr->debug.event = 'I'; /* Increment inflight_hi */
}
if (bbr->round_start)
bbr2_raise_inflight_hi_slope(sk);
}
/* Does loss/ECN rate for this sample say inflight is "too high"?
* This is used by both the bbr_check_loss_too_high_in_startup() function,
* which can be used in either v1 or v2, and the PROBE_UP phase of v2, which
* uses it to notice when loss/ECN rates suggest inflight is too high.
*/
static bool bbr2_is_inflight_too_high(const struct sock *sk,
const struct rate_sample *rs)
{
const struct bbr *bbr = inet_csk_ca(sk);
u32 loss_thresh, ecn_thresh;
if (rs->lost > 0 && rs->tx_in_flight) {
loss_thresh = (u64)rs->tx_in_flight * bbr->params.loss_thresh >>
BBR_SCALE;
if (rs->lost > loss_thresh)
return true;
}
if (rs->delivered_ce > 0 && rs->delivered > 0 &&
bbr->ecn_eligible && bbr->params.ecn_thresh) {
ecn_thresh = (u64)rs->delivered * bbr->params.ecn_thresh >>
BBR_SCALE;
if (rs->delivered_ce >= ecn_thresh)
return true;
}
return false;
}
/* Calculate the tx_in_flight level that corresponded to excessive loss.
* We find "lost_prefix" segs of the skb where loss rate went too high,
* by solving for "lost_prefix" in the following equation:
* lost / inflight >= loss_thresh
* (lost_prev + lost_prefix) / (inflight_prev + lost_prefix) >= loss_thresh
* Then we take that equation, convert it to fixed point, and
* round up to the nearest packet.
*/
static u32 bbr2_inflight_hi_from_lost_skb(const struct sock *sk,
const struct rate_sample *rs,
const struct sk_buff *skb)
{
const struct bbr *bbr = inet_csk_ca(sk);
u32 loss_thresh = bbr->params.loss_thresh;
u32 pcount, divisor, inflight_hi;
s32 inflight_prev, lost_prev;
u64 loss_budget, lost_prefix;
pcount = tcp_skb_pcount(skb);
/* How much data was in flight before this skb? */
inflight_prev = rs->tx_in_flight - pcount;
if (WARN_ONCE(inflight_prev < 0,
"tx_in_flight: %u pcount: %u reneg: %u",
rs->tx_in_flight, pcount, tcp_sk(sk)->is_sack_reneg))
return ~0U;
/* How much inflight data was marked lost before this skb? */
lost_prev = rs->lost - pcount;
if (WARN_ON_ONCE(lost_prev < 0))
return ~0U;
/* At what prefix of this lost skb did losss rate exceed loss_thresh? */
loss_budget = (u64)inflight_prev * loss_thresh + BBR_UNIT - 1;
loss_budget >>= BBR_SCALE;
if (lost_prev >= loss_budget) {
lost_prefix = 0; /* previous losses crossed loss_thresh */
} else {
lost_prefix = loss_budget - lost_prev;
lost_prefix <<= BBR_SCALE;
divisor = BBR_UNIT - loss_thresh;
if (WARN_ON_ONCE(!divisor)) /* loss_thresh is 8 bits */
return ~0U;
do_div(lost_prefix, divisor);
}
inflight_hi = inflight_prev + lost_prefix;
return inflight_hi;
}
/* If loss/ECN rates during probing indicated we may have overfilled a
* buffer, return an operating point that tries to leave unutilized headroom in
* the path for other flows, for fairness convergence and lower RTTs and loss.
*/
static u32 bbr2_inflight_with_headroom(const struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 headroom, headroom_fraction;
if (bbr->inflight_hi == ~0U)
return ~0U;
headroom_fraction = bbr->params.inflight_headroom;
headroom = ((u64)bbr->inflight_hi * headroom_fraction) >> BBR_SCALE;
headroom = max(headroom, 1U);
return max_t(s32, bbr->inflight_hi - headroom,
bbr->params.cwnd_min_target);
}
/* Bound cwnd to a sensible level, based on our current probing state
* machine phase and model of a good inflight level (inflight_lo, inflight_hi).
*/
static void bbr2_bound_cwnd_for_inflight_model(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 cap;
/* tcp_rcv_synsent_state_process() currently calls tcp_ack()
* and thus cong_control() without first initializing us(!).
*/
if (!bbr->initialized)
return;
cap = ~0U;
if (bbr->mode == BBR_PROBE_BW &&
bbr->cycle_idx != BBR_BW_PROBE_CRUISE) {
/* Probe to see if more packets fit in the path. */
cap = bbr->inflight_hi;
} else {
if (bbr->mode == BBR_PROBE_RTT ||
(bbr->mode == BBR_PROBE_BW &&
bbr->cycle_idx == BBR_BW_PROBE_CRUISE))
cap = bbr2_inflight_with_headroom(sk);
}
/* Adapt to any loss/ECN since our last bw probe. */
cap = min(cap, bbr->inflight_lo);
cap = max_t(u32, cap, bbr->params.cwnd_min_target);
tp->snd_cwnd = min(cap, tp->snd_cwnd);
}
/* Estimate a short-term lower bound on the capacity available now, based
* on measurements of the current delivery process and recent history. When we
* are seeing loss/ECN at times when we are not probing bw, then conservatively
* move toward flow balance by multiplicatively cutting our short-term
* estimated safe rate and volume of data (bw_lo and inflight_lo). We use a
* multiplicative decrease in order to converge to a lower capacity in time
* logarithmic in the magnitude of the decrease.
*
* However, we do not cut our short-term estimates lower than the current rate
* and volume of delivered data from this round trip, since from the current
* delivery process we can estimate the measured capacity available now.
*
* Anything faster than that approach would knowingly risk high loss, which can
* cause low bw for Reno/CUBIC and high loss recovery latency for
* request/response flows using any congestion control.
*/
static void bbr2_adapt_lower_bounds(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 ecn_cut, ecn_inflight_lo, beta;
/* We only use lower-bound estimates when not probing bw.
* When probing we need to push inflight higher to probe bw.
*/
if (bbr2_is_probing_bandwidth(sk))
return;
/* ECN response. */
if (bbr->ecn_in_round && bbr->ecn_eligible && bbr->params.ecn_factor) {
/* Reduce inflight to (1 - alpha*ecn_factor). */
ecn_cut = (BBR_UNIT -
((bbr->ecn_alpha * bbr->params.ecn_factor) >>
BBR_SCALE));
if (bbr->inflight_lo == ~0U)
bbr->inflight_lo = tp->snd_cwnd;
ecn_inflight_lo = (u64)bbr->inflight_lo * ecn_cut >> BBR_SCALE;
} else {
ecn_inflight_lo = ~0U;
}
/* Loss response. */
if (bbr->loss_in_round) {
/* Reduce bw and inflight to (1 - beta). */
if (bbr->bw_lo == ~0U)
bbr->bw_lo = bbr_max_bw(sk);
if (bbr->inflight_lo == ~0U)
bbr->inflight_lo = tp->snd_cwnd;
beta = bbr->params.beta;
bbr->bw_lo =
max_t(u32, bbr->bw_latest,
(u64)bbr->bw_lo *
(BBR_UNIT - beta) >> BBR_SCALE);
bbr->inflight_lo =
max_t(u32, bbr->inflight_latest,
(u64)bbr->inflight_lo *
(BBR_UNIT - beta) >> BBR_SCALE);
}
/* Adjust to the lower of the levels implied by loss or ECN. */
bbr->inflight_lo = min(bbr->inflight_lo, ecn_inflight_lo);
}
/* Reset any short-term lower-bound adaptation to congestion, so that we can
* push our inflight up.
*/
static void bbr2_reset_lower_bounds(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->bw_lo = ~0U;
bbr->inflight_lo = ~0U;
}
/* After bw probing (STARTUP/PROBE_UP), reset signals before entering a state
* machine phase where we adapt our lower bound based on congestion signals.
*/
static void bbr2_reset_congestion_signals(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->loss_in_round = 0;
bbr->ecn_in_round = 0;
bbr->loss_in_cycle = 0;
bbr->ecn_in_cycle = 0;
bbr->bw_latest = 0;
bbr->inflight_latest = 0;
}
/* Update (most of) our congestion signals: track the recent rate and volume of
* delivered data, presence of loss, and EWMA degree of ECN marking.
*/
static void bbr2_update_congestion_signals(
struct sock *sk, const struct rate_sample *rs, struct bbr_context *ctx)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u64 bw;
bbr->loss_round_start = 0;
if (rs->interval_us <= 0 || !rs->acked_sacked)
return; /* Not a valid observation */
bw = ctx->sample_bw;
if (!rs->is_app_limited || bw >= bbr_max_bw(sk))
bbr2_take_bw_hi_sample(sk, bw);
bbr->loss_in_round |= (rs->losses > 0);
/* Update rate and volume of delivered data from latest round trip: */
bbr->bw_latest = max_t(u32, bbr->bw_latest, ctx->sample_bw);
bbr->inflight_latest = max_t(u32, bbr->inflight_latest, rs->delivered);
if (before(rs->prior_delivered, bbr->loss_round_delivered))
return; /* skip the per-round-trip updates */
/* Now do per-round-trip updates. */
bbr->loss_round_delivered = tp->delivered; /* mark round trip */
bbr->loss_round_start = 1;
bbr2_adapt_lower_bounds(sk);
/* Update windowed "latest" (single-round-trip) filters. */
bbr->loss_in_round = 0;
bbr->ecn_in_round = 0;
bbr->bw_latest = ctx->sample_bw;
bbr->inflight_latest = rs->delivered;
}
/* Bandwidth probing can cause loss. To help coexistence with loss-based
* congestion control we spread out our probing in a Reno-conscious way. Due to
* the shape of the Reno sawtooth, the time required between loss epochs for an
* idealized Reno flow is a number of round trips that is the BDP of that
* flow. We count packet-timed round trips directly, since measured RTT can
* vary widely, and Reno is driven by packet-timed round trips.
*/
static bool bbr2_is_reno_coexistence_probe_time(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 inflight, rounds, reno_gain, reno_rounds;
/* Random loss can shave some small percentage off of our inflight
* in each round. To survive this, flows need robust periodic probes.
*/
rounds = bbr->params.bw_probe_max_rounds;
reno_gain = bbr->params.bw_probe_reno_gain;
if (reno_gain) {
inflight = bbr2_target_inflight(sk);
reno_rounds = ((u64)inflight * reno_gain) >> BBR_SCALE;
rounds = min(rounds, reno_rounds);
}
return bbr->rounds_since_probe >= rounds;
}
/* How long do we want to wait before probing for bandwidth (and risking
* loss)? We randomize the wait, for better mixing and fairness convergence.
*
* We bound the Reno-coexistence inter-bw-probe time to be 62-63 round trips.
* This is calculated to allow fairness with a 25Mbps, 30ms Reno flow,
* (eg 4K video to a broadband user):
* BDP = 25Mbps * .030sec /(1514bytes) = 61.9 packets
*
* We bound the BBR-native inter-bw-probe wall clock time to be:
* (a) higher than 2 sec: to try to avoid causing loss for a long enough time
* to allow Reno at 30ms to get 4K video bw, the inter-bw-probe time must
* be at least: 25Mbps * .030sec / (1514bytes) * 0.030sec = 1.9secs
* (b) lower than 3 sec: to ensure flows can start probing in a reasonable
* amount of time to discover unutilized bw on human-scale interactive
* time-scales (e.g. perhaps traffic from a web page download that we
* were competing with is now complete).
*/
static void bbr2_pick_probe_wait(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
/* Decide the random round-trip bound for wait until probe: */
bbr->rounds_since_probe =
get_random_u32_below(bbr->params.bw_probe_rand_rounds);
/* Decide the random wall clock bound for wait until probe: */
bbr->probe_wait_us = bbr->params.bw_probe_base_us +
get_random_u32_below(bbr->params.bw_probe_rand_us);
}
static void bbr2_set_cycle_idx(struct sock *sk, int cycle_idx)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->cycle_idx = cycle_idx;
/* New phase, so need to update cwnd and pacing rate. */
bbr->try_fast_path = 0;
}
/* Send at estimated bw to fill the pipe, but not queue. We need this phase
* before PROBE_UP, because as soon as we send faster than the available bw
* we will start building a queue, and if the buffer is shallow we can cause
* loss. If we do not fill the pipe before we cause this loss, our bw_hi and
* inflight_hi estimates will underestimate.
*/
static void bbr2_start_bw_probe_refill(struct sock *sk, u32 bw_probe_up_rounds)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr2_reset_lower_bounds(sk);
if (bbr->inflight_hi != ~0U)
bbr->inflight_hi += bbr->params.refill_add_inc;
bbr->bw_probe_up_rounds = bw_probe_up_rounds;
bbr->bw_probe_up_acks = 0;
bbr->stopped_risky_probe = 0;
bbr->ack_phase = BBR_ACKS_REFILLING;
bbr->next_rtt_delivered = tp->delivered;
bbr2_set_cycle_idx(sk, BBR_BW_PROBE_REFILL);
}
/* Now probe max deliverable data rate and volume. */
static void bbr2_start_bw_probe_up(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr->ack_phase = BBR_ACKS_PROBE_STARTING;
bbr->next_rtt_delivered = tp->delivered;
bbr->cycle_mstamp = tp->tcp_mstamp;
bbr2_set_cycle_idx(sk, BBR_BW_PROBE_UP);
bbr2_raise_inflight_hi_slope(sk);
}
/* Start a new PROBE_BW probing cycle of some wall clock length. Pick a wall
* clock time at which to probe beyond an inflight that we think to be
* safe. This will knowingly risk packet loss, so we want to do this rarely, to
* keep packet loss rates low. Also start a round-trip counter, to probe faster
* if we estimate a Reno flow at our BDP would probe faster.
*/
static void bbr2_start_bw_probe_down(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr2_reset_congestion_signals(sk);
bbr->bw_probe_up_cnt = ~0U; /* not growing inflight_hi any more */
bbr2_pick_probe_wait(sk);
bbr->cycle_mstamp = tp->tcp_mstamp; /* start wall clock */
bbr->ack_phase = BBR_ACKS_PROBE_STOPPING;
bbr->next_rtt_delivered = tp->delivered;
bbr2_set_cycle_idx(sk, BBR_BW_PROBE_DOWN);
}
/* Cruise: maintain what we estimate to be a neutral, conservative
* operating point, without attempting to probe up for bandwidth or down for
* RTT, and only reducing inflight in response to loss/ECN signals.
*/
static void bbr2_start_bw_probe_cruise(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->inflight_lo != ~0U)
bbr->inflight_lo = min(bbr->inflight_lo, bbr->inflight_hi);
bbr2_set_cycle_idx(sk, BBR_BW_PROBE_CRUISE);
}
/* Loss and/or ECN rate is too high while probing.
* Adapt (once per bw probe) by cutting inflight_hi and then restarting cycle.
*/
static void bbr2_handle_inflight_too_high(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
const u32 beta = bbr->params.beta;
bbr->prev_probe_too_high = 1;
bbr->bw_probe_samples = 0; /* only react once per probe */
bbr->debug.event = 'L'; /* Loss/ECN too high */
/* If we are app-limited then we are not robustly
* probing the max volume of inflight data we think
* might be safe (analogous to how app-limited bw
* samples are not known to be robustly probing bw).
*/
if (!rs->is_app_limited)
bbr->inflight_hi = max_t(u32, rs->tx_in_flight,
(u64)bbr2_target_inflight(sk) *
(BBR_UNIT - beta) >> BBR_SCALE);
if (bbr->mode == BBR_PROBE_BW && bbr->cycle_idx == BBR_BW_PROBE_UP)
bbr2_start_bw_probe_down(sk);
}
/* If we're seeing bw and loss samples reflecting our bw probing, adapt
* using the signals we see. If loss or ECN mark rate gets too high, then adapt
* inflight_hi downward. If we're able to push inflight higher without such
* signals, push higher: adapt inflight_hi upward.
*/
static bool bbr2_adapt_upper_bounds(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
/* Track when we'll see bw/loss samples resulting from our bw probes. */
if (bbr->ack_phase == BBR_ACKS_PROBE_STARTING && bbr->round_start)
bbr->ack_phase = BBR_ACKS_PROBE_FEEDBACK;
if (bbr->ack_phase == BBR_ACKS_PROBE_STOPPING && bbr->round_start) {
/* End of samples from bw probing phase. */
bbr->bw_probe_samples = 0;
bbr->ack_phase = BBR_ACKS_INIT;
/* At this point in the cycle, our current bw sample is also
* our best recent chance at finding the highest available bw
* for this flow. So now is the best time to forget the bw
* samples from the previous cycle, by advancing the window.
*/
if (bbr->mode == BBR_PROBE_BW && !rs->is_app_limited)
bbr2_advance_bw_hi_filter(sk);
/* If we had an inflight_hi, then probed and pushed inflight all
* the way up to hit that inflight_hi without seeing any
* high loss/ECN in all the resulting ACKs from that probing,
* then probe up again, this time letting inflight persist at
* inflight_hi for a round trip, then accelerating beyond.
*/
if (bbr->mode == BBR_PROBE_BW &&
bbr->stopped_risky_probe && !bbr->prev_probe_too_high) {
bbr->debug.event = 'R'; /* reprobe */
bbr2_start_bw_probe_refill(sk, 0);
return true; /* yes, decided state transition */
}
}
if (bbr2_is_inflight_too_high(sk, rs)) {
if (bbr->bw_probe_samples) /* sample is from bw probing? */
bbr2_handle_inflight_too_high(sk, rs);
} else {
/* Loss/ECN rate is declared safe. Adjust upper bound upward. */
if (bbr->inflight_hi == ~0U) /* no excess queue signals yet? */
return false;
/* To be resilient to random loss, we must raise inflight_hi
* if we observe in any phase that a higher level is safe.
*/
if (rs->tx_in_flight > bbr->inflight_hi) {
bbr->inflight_hi = rs->tx_in_flight;
bbr->debug.event = 'U'; /* raise up inflight_hi */
}
if (bbr->mode == BBR_PROBE_BW &&
bbr->cycle_idx == BBR_BW_PROBE_UP)
bbr2_probe_inflight_hi_upward(sk, rs);
}
return false;
}
/* Check if it's time to probe for bandwidth now, and if so, kick it off. */
static bool bbr2_check_time_to_probe_bw(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 n;
/* If we seem to be at an operating point where we are not seeing loss
* but we are seeing ECN marks, then when the ECN marks cease we reprobe
* quickly (in case a burst of cross-traffic has ceased and freed up bw,
* or in case we are sharing with multiplicatively probing traffic).
*/
if (bbr->params.ecn_reprobe_gain && bbr->ecn_eligible &&
bbr->ecn_in_cycle && !bbr->loss_in_cycle &&
inet_csk(sk)->icsk_ca_state == TCP_CA_Open) {
bbr->debug.event = 'A'; /* *A*ll clear to probe *A*gain */
/* Calculate n so that when bbr2_raise_inflight_hi_slope()
* computes growth_this_round as 2^n it will be roughly the
* desired volume of data (inflight_hi*ecn_reprobe_gain).
*/
n = ilog2((((u64)bbr->inflight_hi *
bbr->params.ecn_reprobe_gain) >> BBR_SCALE));
bbr2_start_bw_probe_refill(sk, n);
return true;
}
if (bbr2_has_elapsed_in_phase(sk, bbr->probe_wait_us) ||
bbr2_is_reno_coexistence_probe_time(sk)) {
bbr2_start_bw_probe_refill(sk, 0);
return true;
}
return false;
}
/* Is it time to transition from PROBE_DOWN to PROBE_CRUISE? */
static bool bbr2_check_time_to_cruise(struct sock *sk, u32 inflight, u32 bw)
{
struct bbr *bbr = inet_csk_ca(sk);
bool is_under_bdp, is_long_enough;
/* Always need to pull inflight down to leave headroom in queue. */
if (inflight > bbr2_inflight_with_headroom(sk))
return false;
is_under_bdp = inflight <= bbr_inflight(sk, bw, BBR_UNIT);
if (bbr->params.drain_to_target)
return is_under_bdp;
is_long_enough = bbr2_has_elapsed_in_phase(sk, bbr->min_rtt_us);
return is_under_bdp || is_long_enough;
}
/* PROBE_BW state machine: cruise, refill, probe for bw, or drain? */
static void bbr2_update_cycle_phase(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
bool is_risky = false, is_queuing = false;
u32 inflight, bw;
if (!bbr_full_bw_reached(sk))
return;
/* In DRAIN, PROBE_BW, or PROBE_RTT, adjust upper bounds. */
if (bbr2_adapt_upper_bounds(sk, rs))
return; /* already decided state transition */
if (bbr->mode != BBR_PROBE_BW)
return;
inflight = bbr_packets_in_net_at_edt(sk, rs->prior_in_flight);
bw = bbr_max_bw(sk);
switch (bbr->cycle_idx) {
/* First we spend most of our time cruising with a pacing_gain of 1.0,
* which paces at the estimated bw, to try to fully use the pipe
* without building queue. If we encounter loss/ECN marks, we adapt
* by slowing down.
*/
case BBR_BW_PROBE_CRUISE:
if (bbr2_check_time_to_probe_bw(sk))
return; /* already decided state transition */
break;
/* After cruising, when it's time to probe, we first "refill": we send
* at the estimated bw to fill the pipe, before probing higher and
* knowingly risking overflowing the bottleneck buffer (causing loss).
*/
case BBR_BW_PROBE_REFILL:
if (bbr->round_start) {
/* After one full round trip of sending in REFILL, we
* start to see bw samples reflecting our REFILL, which
* may be putting too much data in flight.
*/
bbr->bw_probe_samples = 1;
bbr2_start_bw_probe_up(sk);
}
break;
/* After we refill the pipe, we probe by using a pacing_gain > 1.0, to
* probe for bw. If we have not seen loss/ECN, we try to raise inflight
* to at least pacing_gain*BDP; note that this may take more than
* min_rtt if min_rtt is small (e.g. on a LAN).
*
* We terminate PROBE_UP bandwidth probing upon any of the following:
*
* (1) We've pushed inflight up to hit the inflight_hi target set in the
* most recent previous bw probe phase. Thus we want to start
* draining the queue immediately because it's very likely the most
* recently sent packets will fill the queue and cause drops.
* (checked here)
* (2) We have probed for at least 1*min_rtt_us, and the
* estimated queue is high enough (inflight > 1.25 * estimated_bdp).
* (checked here)
* (3) Loss filter says loss rate is "too high".
* (checked in bbr_is_inflight_too_high())
* (4) ECN filter says ECN mark rate is "too high".
* (checked in bbr_is_inflight_too_high())
*/
case BBR_BW_PROBE_UP:
if (bbr->prev_probe_too_high &&
inflight >= bbr->inflight_hi) {
bbr->stopped_risky_probe = 1;
is_risky = true;
bbr->debug.event = 'D'; /* D for danger */
} else if (bbr2_has_elapsed_in_phase(sk, bbr->min_rtt_us) &&
inflight >=
bbr_inflight(sk, bw,
bbr->params.bw_probe_pif_gain)) {
is_queuing = true;
bbr->debug.event = 'Q'; /* building Queue */
}
if (is_risky || is_queuing) {
bbr->prev_probe_too_high = 0; /* no loss/ECN (yet) */
bbr2_start_bw_probe_down(sk); /* restart w/ down */
}
break;
/* After probing in PROBE_UP, we have usually accumulated some data in
* the bottleneck buffer (if bw probing didn't find more bw). We next
* enter PROBE_DOWN to try to drain any excess data from the queue. To
* do this, we use a pacing_gain < 1.0. We hold this pacing gain until
* our inflight is less then that target cruising point, which is the
* minimum of (a) the amount needed to leave headroom, and (b) the
* estimated BDP. Once inflight falls to match the target, we estimate
* the queue is drained; persisting would underutilize the pipe.
*/
case BBR_BW_PROBE_DOWN:
if (bbr2_check_time_to_probe_bw(sk))
return; /* already decided state transition */
if (bbr2_check_time_to_cruise(sk, inflight, bw))
bbr2_start_bw_probe_cruise(sk);
break;
default:
WARN_ONCE(1, "BBR invalid cycle index %u\n", bbr->cycle_idx);
}
}
/* Exiting PROBE_RTT, so return to bandwidth probing in STARTUP or PROBE_BW. */
static void bbr2_exit_probe_rtt(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr2_reset_lower_bounds(sk);
if (bbr_full_bw_reached(sk)) {
bbr->mode = BBR_PROBE_BW;
/* Raising inflight after PROBE_RTT may cause loss, so reset
* the PROBE_BW clock and schedule the next bandwidth probe for
* a friendly and randomized future point in time.
*/
bbr2_start_bw_probe_down(sk);
/* Since we are exiting PROBE_RTT, we know inflight is
* below our estimated BDP, so it is reasonable to cruise.
*/
bbr2_start_bw_probe_cruise(sk);
} else {
bbr->mode = BBR_STARTUP;
}
}
/* Exit STARTUP based on loss rate > 1% and loss gaps in round >= N. Wait until
* the end of the round in recovery to get a good estimate of how many packets
* have been lost, and how many we need to drain with a low pacing rate.
*/
static void bbr2_check_loss_too_high_in_startup(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr_full_bw_reached(sk))
return;
/* For STARTUP exit, check the loss rate at the end of each round trip
* of Recovery episodes in STARTUP. We check the loss rate at the end
* of the round trip to filter out noisy/low loss and have a better
* sense of inflight (extent of loss), so we can drain more accurately.
*/
if (rs->losses && bbr->loss_events_in_round < 0xf)
bbr->loss_events_in_round++; /* update saturating counter */
if (bbr->params.full_loss_cnt && bbr->loss_round_start &&
inet_csk(sk)->icsk_ca_state == TCP_CA_Recovery &&
bbr->loss_events_in_round >= bbr->params.full_loss_cnt &&
bbr2_is_inflight_too_high(sk, rs)) {
bbr->debug.event = 'P'; /* Packet loss caused STARTUP exit */
bbr2_handle_queue_too_high_in_startup(sk);
return;
}
if (bbr->loss_round_start)
bbr->loss_events_in_round = 0;
}
/* If we are done draining, advance into steady state operation in PROBE_BW. */
static void bbr2_check_drain(struct sock *sk, const struct rate_sample *rs,
struct bbr_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr_check_drain(sk, rs, ctx)) {
bbr->mode = BBR_PROBE_BW;
bbr2_start_bw_probe_down(sk);
}
}
static void bbr2_update_model(struct sock *sk, const struct rate_sample *rs,
struct bbr_context *ctx)
{
bbr2_update_congestion_signals(sk, rs, ctx);
bbr_update_ack_aggregation(sk, rs);
bbr2_check_loss_too_high_in_startup(sk, rs);
bbr_check_full_bw_reached(sk, rs);
bbr2_check_drain(sk, rs, ctx);
bbr2_update_cycle_phase(sk, rs);
bbr_update_min_rtt(sk, rs);
}
/* Fast path for app-limited case.
*
* On each ack, we execute bbr state machine, which primarily consists of:
* 1) update model based on new rate sample, and
* 2) update control based on updated model or state change.
*
* There are certain workload/scenarios, e.g. app-limited case, where
* either we can skip updating model or we can skip update of both model
* as well as control. This provides signifcant softirq cpu savings for
* processing incoming acks.
*
* In case of app-limited, if there is no congestion (loss/ecn) and
* if observed bw sample is less than current estimated bw, then we can
* skip some of the computation in bbr state processing:
*
* - if there is no rtt/mode/phase change: In this case, since all the
* parameters of the network model are constant, we can skip model
* as well control update.
*
* - else we can skip rest of the model update. But we still need to
* update the control to account for the new rtt/mode/phase.
*
* Returns whether we can take fast path or not.
*/
static bool bbr2_fast_path(struct sock *sk, bool *update_model,
const struct rate_sample *rs, struct bbr_context *ctx)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 prev_min_rtt_us, prev_mode;
if (bbr->params.fast_path && bbr->try_fast_path &&
rs->is_app_limited && ctx->sample_bw < bbr_max_bw(sk) &&
!bbr->loss_in_round && !bbr->ecn_in_round) {
prev_mode = bbr->mode;
prev_min_rtt_us = bbr->min_rtt_us;
bbr2_check_drain(sk, rs, ctx);
bbr2_update_cycle_phase(sk, rs);
bbr_update_min_rtt(sk, rs);
if (bbr->mode == prev_mode &&
bbr->min_rtt_us == prev_min_rtt_us &&
bbr->try_fast_path)
return true;
/* Skip model update, but control still needs to be updated */
*update_model = false;
}
return false;
}
static void bbr2_main(struct sock *sk, const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
struct bbr_context ctx = { 0 };
bool update_model = true;
u32 bw;
bbr->debug.event = '.'; /* init to default NOP (no event yet) */
bbr_update_round_start(sk, rs, &ctx);
if (bbr->round_start) {
bbr->rounds_since_probe =
min_t(s32, bbr->rounds_since_probe + 1, 0xFF);
bbr2_update_ecn_alpha(sk);
}
bbr->ecn_in_round |= rs->is_ece;
bbr_calculate_bw_sample(sk, rs, &ctx);
if (bbr2_fast_path(sk, &update_model, rs, &ctx))
goto out;
if (update_model)
bbr2_update_model(sk, rs, &ctx);
bbr_update_gains(sk);
bw = bbr_bw(sk);
bbr_set_pacing_rate(sk, bw, bbr->pacing_gain);
bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain,
tp->snd_cwnd, &ctx);
bbr2_bound_cwnd_for_inflight_model(sk);
out:
bbr->prev_ca_state = inet_csk(sk)->icsk_ca_state;
bbr->loss_in_cycle |= rs->lost > 0;
bbr->ecn_in_cycle |= rs->delivered_ce > 0;
bbr_debug(sk, rs->acked_sacked, rs, &ctx);
}
/* Module parameters that are settable by TCP_CONGESTION_PARAMS are declared
* down here, so that the algorithm functions that use the parameters must use
* the per-socket parameters; if they accidentally use the global version
* then there will be a compile error.
* TODO(ncardwell): move all per-socket parameters down to this section.
*/
/* On losses, scale down inflight and pacing rate by beta scaled by BBR_SCALE.
* No loss response when 0. Max allwed value is 255.
*/
static u32 bbr_beta = BBR_UNIT * 30 / 100;
/* Gain factor for ECN mark ratio samples, scaled by BBR_SCALE.
* Max allowed value is 255.
*/
static u32 bbr_ecn_alpha_gain = BBR_UNIT * 1 / 16; /* 1/16 = 6.25% */
/* The initial value for the ecn_alpha state variable. Default and max
* BBR_UNIT (256), representing 1.0. This allows a flow to respond quickly
* to congestion if the bottleneck is congested when the flow starts up.
*/
static u32 bbr_ecn_alpha_init = BBR_UNIT; /* 1.0, to respond quickly */
/* On ECN, cut inflight_lo to (1 - ecn_factor * ecn_alpha) scaled by BBR_SCALE.
* No ECN based bounding when 0. Max allwed value is 255.
*/
static u32 bbr_ecn_factor = BBR_UNIT * 1 / 3; /* 1/3 = 33% */
/* Estimate bw probing has gone too far if CE ratio exceeds this threshold.
* Scaled by BBR_SCALE. Disabled when 0. Max allowed is 255.
*/
static u32 bbr_ecn_thresh = BBR_UNIT * 1 / 2; /* 1/2 = 50% */
/* Max RTT (in usec) at which to use sender-side ECN logic.
* Disabled when 0 (ECN allowed at any RTT).
* Max allowed for the parameter is 524287 (0x7ffff) us, ~524 ms.
*/
static u32 bbr_ecn_max_rtt_us = 5000;
/* If non-zero, if in a cycle with no losses but some ECN marks, after ECN
* clears then use a multiplicative increase to quickly reprobe bw by
* starting inflight probing at the given multiple of inflight_hi.
* Default for this experimental knob is 0 (disabled).
* Planned value for experiments: BBR_UNIT * 1 / 2 = 128, representing 0.5.
*/
static u32 bbr_ecn_reprobe_gain;
/* Estimate bw probing has gone too far if loss rate exceeds this level. */
static u32 bbr_loss_thresh = BBR_UNIT * 2 / 100; /* 2% loss */
/* Exit STARTUP if number of loss marking events in a Recovery round is >= N,
* and loss rate is higher than bbr_loss_thresh.
* Disabled if 0. Max allowed value is 15 (0xF).
*/
static u32 bbr_full_loss_cnt = 8;
/* Exit STARTUP if number of round trips with ECN mark rate above ecn_thresh
* meets this count. Max allowed value is 3.
*/
static u32 bbr_full_ecn_cnt = 2;
/* Fraction of unutilized headroom to try to leave in path upon high loss. */
static u32 bbr_inflight_headroom = BBR_UNIT * 15 / 100;
/* Multiplier to get target inflight (as multiple of BDP) for PROBE_UP phase.
* Default is 1.25x, as in BBR v1. Max allowed is 511.
*/
static u32 bbr_bw_probe_pif_gain = BBR_UNIT * 5 / 4;
/* Multiplier to get Reno-style probe epoch duration as: k * BDP round trips.
* If zero, disables this BBR v2 Reno-style BDP-scaled coexistence mechanism.
* Max allowed is 511.
*/
static u32 bbr_bw_probe_reno_gain = BBR_UNIT;
/* Max number of packet-timed rounds to wait before probing for bandwidth. If
* we want to tolerate 1% random loss per round, and not have this cut our
* inflight too much, we must probe for bw periodically on roughly this scale.
* If low, limits Reno/CUBIC coexistence; if high, limits loss tolerance.
* We aim to be fair with Reno/CUBIC up to a BDP of at least:
* BDP = 25Mbps * .030sec /(1514bytes) = 61.9 packets
*/
static u32 bbr_bw_probe_max_rounds = 63;
/* Max amount of randomness to inject in round counting for Reno-coexistence.
* Max value is 15.
*/
static u32 bbr_bw_probe_rand_rounds = 2;
/* Use BBR-native probe time scale starting at this many usec.
* We aim to be fair with Reno/CUBIC up to an inter-loss time epoch of at least:
* BDP*RTT = 25Mbps * .030sec /(1514bytes) * 0.030sec = 1.9 secs
*/
static u32 bbr_bw_probe_base_us = 2 * USEC_PER_SEC; /* 2 secs */
/* Use BBR-native probes spread over this many usec: */
static u32 bbr_bw_probe_rand_us = 1 * USEC_PER_SEC; /* 1 secs */
/* Undo the model changes made in loss recovery if recovery was spurious? */
static bool bbr_undo = true;
/* Use fast path if app-limited, no loss/ECN, and target cwnd was reached? */
static bool bbr_fast_path = true; /* default: enabled */
/* Use fast ack mode ? */
static int bbr_fast_ack_mode = 1; /* default: rwnd check off */
/* How much to additively increase inflight_hi when entering REFILL? */
static u32 bbr_refill_add_inc; /* default: disabled */
module_param_named(beta, bbr_beta, uint, 0644);
module_param_named(ecn_alpha_gain, bbr_ecn_alpha_gain, uint, 0644);
module_param_named(ecn_alpha_init, bbr_ecn_alpha_init, uint, 0644);
module_param_named(ecn_factor, bbr_ecn_factor, uint, 0644);
module_param_named(ecn_thresh, bbr_ecn_thresh, uint, 0644);
module_param_named(ecn_max_rtt_us, bbr_ecn_max_rtt_us, uint, 0644);
module_param_named(ecn_reprobe_gain, bbr_ecn_reprobe_gain, uint, 0644);
module_param_named(loss_thresh, bbr_loss_thresh, uint, 0664);
module_param_named(full_loss_cnt, bbr_full_loss_cnt, uint, 0664);
module_param_named(full_ecn_cnt, bbr_full_ecn_cnt, uint, 0664);
module_param_named(inflight_headroom, bbr_inflight_headroom, uint, 0664);
module_param_named(bw_probe_pif_gain, bbr_bw_probe_pif_gain, uint, 0664);
module_param_named(bw_probe_reno_gain, bbr_bw_probe_reno_gain, uint, 0664);
module_param_named(bw_probe_max_rounds, bbr_bw_probe_max_rounds, uint, 0664);
module_param_named(bw_probe_rand_rounds, bbr_bw_probe_rand_rounds, uint, 0664);
module_param_named(bw_probe_base_us, bbr_bw_probe_base_us, uint, 0664);
module_param_named(bw_probe_rand_us, bbr_bw_probe_rand_us, uint, 0664);
module_param_named(undo, bbr_undo, bool, 0664);
module_param_named(fast_path, bbr_fast_path, bool, 0664);
module_param_named(fast_ack_mode, bbr_fast_ack_mode, uint, 0664);
module_param_named(refill_add_inc, bbr_refill_add_inc, uint, 0664);
static void bbr2_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr_init(sk); /* run shared init code for v1 and v2 */
/* BBR v2 parameters: */
bbr->params.beta = min_t(u32, 0xFFU, bbr_beta);
bbr->params.ecn_alpha_gain = min_t(u32, 0xFFU, bbr_ecn_alpha_gain);
bbr->params.ecn_alpha_init = min_t(u32, BBR_UNIT, bbr_ecn_alpha_init);
bbr->params.ecn_factor = min_t(u32, 0xFFU, bbr_ecn_factor);
bbr->params.ecn_thresh = min_t(u32, 0xFFU, bbr_ecn_thresh);
bbr->params.ecn_max_rtt_us = min_t(u32, 0x7ffffU, bbr_ecn_max_rtt_us);
bbr->params.ecn_reprobe_gain = min_t(u32, 0x1FF, bbr_ecn_reprobe_gain);
bbr->params.loss_thresh = min_t(u32, 0xFFU, bbr_loss_thresh);
bbr->params.full_loss_cnt = min_t(u32, 0xFU, bbr_full_loss_cnt);
bbr->params.full_ecn_cnt = min_t(u32, 0x3U, bbr_full_ecn_cnt);
bbr->params.inflight_headroom =
min_t(u32, 0xFFU, bbr_inflight_headroom);
bbr->params.bw_probe_pif_gain =
min_t(u32, 0x1FFU, bbr_bw_probe_pif_gain);
bbr->params.bw_probe_reno_gain =
min_t(u32, 0x1FFU, bbr_bw_probe_reno_gain);
bbr->params.bw_probe_max_rounds =
min_t(u32, 0xFFU, bbr_bw_probe_max_rounds);
bbr->params.bw_probe_rand_rounds =
min_t(u32, 0xFU, bbr_bw_probe_rand_rounds);
bbr->params.bw_probe_base_us =
min_t(u32, (1 << 26) - 1, bbr_bw_probe_base_us);
bbr->params.bw_probe_rand_us =
min_t(u32, (1 << 26) - 1, bbr_bw_probe_rand_us);
bbr->params.undo = bbr_undo;
bbr->params.fast_path = bbr_fast_path ? 1 : 0;
bbr->params.refill_add_inc = min_t(u32, 0x3U, bbr_refill_add_inc);
/* BBR v2 state: */
bbr->initialized = 1;
/* Start sampling ECN mark rate after first full flight is ACKed: */
bbr->loss_round_delivered = tp->delivered + 1;
bbr->loss_round_start = 0;
bbr->undo_bw_lo = 0;
bbr->undo_inflight_lo = 0;
bbr->undo_inflight_hi = 0;
bbr->loss_events_in_round = 0;
bbr->startup_ecn_rounds = 0;
bbr2_reset_congestion_signals(sk);
bbr->bw_lo = ~0U;
bbr->bw_hi[0] = 0;
bbr->bw_hi[1] = 0;
bbr->inflight_lo = ~0U;
bbr->inflight_hi = ~0U;
bbr->bw_probe_up_cnt = ~0U;
bbr->bw_probe_up_acks = 0;
bbr->bw_probe_up_rounds = 0;
bbr->probe_wait_us = 0;
bbr->stopped_risky_probe = 0;
bbr->ack_phase = BBR_ACKS_INIT;
bbr->rounds_since_probe = 0;
bbr->bw_probe_samples = 0;
bbr->prev_probe_too_high = 0;
bbr->ecn_eligible = 0;
bbr->ecn_alpha = bbr->params.ecn_alpha_init;
bbr->alpha_last_delivered = 0;
bbr->alpha_last_delivered_ce = 0;
tp->fast_ack_mode = min_t(u32, 0x2U, bbr_fast_ack_mode);
if ((tp->ecn_flags & TCP_ECN_OK) && bbr_ecn_enable)
tp->ecn_flags |= TCP_ECN_ECT_PERMANENT;
}
/* Core TCP stack informs us that the given skb was just marked lost. */
static void bbr2_skb_marked_lost(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
struct rate_sample rs;
/* Capture "current" data over the full round trip of loss,
* to have a better chance to see the full capacity of the path.
*/
if (!bbr->loss_in_round) /* first loss in this round trip? */
bbr->loss_round_delivered = tp->delivered; /* set round trip */
bbr->loss_in_round = 1;
bbr->loss_in_cycle = 1;
if (!bbr->bw_probe_samples)
return; /* not an skb sent while probing for bandwidth */
if (unlikely(!scb->tx.delivered_mstamp))
return; /* skb was SACKed, reneged, marked lost; ignore it */
/* We are probing for bandwidth. Construct a rate sample that
* estimates what happened in the flight leading up to this lost skb,
* then see if the loss rate went too high, and if so at which packet.
*/
memset(&rs, 0, sizeof(rs));
rs.tx_in_flight = scb->tx.in_flight;
rs.lost = tp->lost - scb->tx.lost;
rs.is_app_limited = scb->tx.is_app_limited;
if (bbr2_is_inflight_too_high(sk, &rs)) {
rs.tx_in_flight = bbr2_inflight_hi_from_lost_skb(sk, &rs, skb);
bbr2_handle_inflight_too_high(sk, &rs);
}
}
/* Revert short-term model if current loss recovery event was spurious. */
static u32 bbr2_undo_cwnd(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr->debug.undo = 1;
bbr->full_bw = 0; /* spurious slow-down; reset full pipe detection */
bbr->full_bw_cnt = 0;
bbr->loss_in_round = 0;
if (!bbr->params.undo)
return tp->snd_cwnd;
/* Revert to cwnd and other state saved before loss episode. */
bbr->bw_lo = max(bbr->bw_lo, bbr->undo_bw_lo);
bbr->inflight_lo = max(bbr->inflight_lo, bbr->undo_inflight_lo);
bbr->inflight_hi = max(bbr->inflight_hi, bbr->undo_inflight_hi);
return bbr->prior_cwnd;
}
/* Entering loss recovery, so save state for when we undo recovery. */
static u32 bbr2_ssthresh(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr_save_cwnd(sk);
/* For undo, save state that adapts based on loss signal. */
bbr->undo_bw_lo = bbr->bw_lo;
bbr->undo_inflight_lo = bbr->inflight_lo;
bbr->undo_inflight_hi = bbr->inflight_hi;
return tcp_sk(sk)->snd_ssthresh;
}
static enum tcp_bbr2_phase bbr2_get_phase(struct bbr *bbr)
{
switch (bbr->mode) {
case BBR_STARTUP:
return BBR2_PHASE_STARTUP;
case BBR_DRAIN:
return BBR2_PHASE_DRAIN;
case BBR_PROBE_BW:
break;
case BBR_PROBE_RTT:
return BBR2_PHASE_PROBE_RTT;
default:
return BBR2_PHASE_INVALID;
}
switch (bbr->cycle_idx) {
case BBR_BW_PROBE_UP:
return BBR2_PHASE_PROBE_BW_UP;
case BBR_BW_PROBE_DOWN:
return BBR2_PHASE_PROBE_BW_DOWN;
case BBR_BW_PROBE_CRUISE:
return BBR2_PHASE_PROBE_BW_CRUISE;
case BBR_BW_PROBE_REFILL:
return BBR2_PHASE_PROBE_BW_REFILL;
default:
return BBR2_PHASE_INVALID;
}
}
static size_t bbr2_get_info(struct sock *sk, u32 ext, int *attr,
union tcp_cc_info *info)
{
if (ext & (1 << (INET_DIAG_BBRINFO - 1)) ||
ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
struct bbr *bbr = inet_csk_ca(sk);
u64 bw = bbr_bw_bytes_per_sec(sk, bbr_bw(sk));
u64 bw_hi = bbr_bw_bytes_per_sec(sk, bbr_max_bw(sk));
u64 bw_lo = bbr->bw_lo == ~0U ?
~0ULL : bbr_bw_bytes_per_sec(sk, bbr->bw_lo);
memset(&info->bbr2, 0, sizeof(info->bbr2));
info->bbr2.bbr_bw_lsb = (u32)bw;
info->bbr2.bbr_bw_msb = (u32)(bw >> 32);
info->bbr2.bbr_min_rtt = bbr->min_rtt_us;
info->bbr2.bbr_pacing_gain = bbr->pacing_gain;
info->bbr2.bbr_cwnd_gain = bbr->cwnd_gain;
info->bbr2.bbr_bw_hi_lsb = (u32)bw_hi;
info->bbr2.bbr_bw_hi_msb = (u32)(bw_hi >> 32);
info->bbr2.bbr_bw_lo_lsb = (u32)bw_lo;
info->bbr2.bbr_bw_lo_msb = (u32)(bw_lo >> 32);
info->bbr2.bbr_mode = bbr->mode;
info->bbr2.bbr_phase = (__u8)bbr2_get_phase(bbr);
info->bbr2.bbr_version = (__u8)2;
info->bbr2.bbr_inflight_lo = bbr->inflight_lo;
info->bbr2.bbr_inflight_hi = bbr->inflight_hi;
info->bbr2.bbr_extra_acked = bbr_extra_acked(sk);
*attr = INET_DIAG_BBRINFO;
return sizeof(info->bbr2);
}
return 0;
}
static void bbr2_set_state(struct sock *sk, u8 new_state)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (new_state == TCP_CA_Loss) {
struct rate_sample rs = { .losses = 1 };
struct bbr_context ctx = { 0 };
bbr->prev_ca_state = TCP_CA_Loss;
bbr->full_bw = 0;
if (!bbr2_is_probing_bandwidth(sk) && bbr->inflight_lo == ~0U) {
/* bbr_adapt_lower_bounds() needs cwnd before
* we suffered an RTO, to update inflight_lo:
*/
bbr->inflight_lo =
max(tp->snd_cwnd, bbr->prior_cwnd);
}
bbr_debug(sk, 0, &rs, &ctx);
} else if (bbr->prev_ca_state == TCP_CA_Loss &&
new_state != TCP_CA_Loss) {
tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd);
bbr->try_fast_path = 0; /* bound cwnd using latest model */
}
}
static struct tcp_congestion_ops tcp_bbr2_cong_ops __read_mostly = {
.flags = TCP_CONG_NON_RESTRICTED | TCP_CONG_WANTS_CE_EVENTS,
.name = "bbr2",
.owner = THIS_MODULE,
.init = bbr2_init,
.cong_control = bbr2_main,
.sndbuf_expand = bbr_sndbuf_expand,
.skb_marked_lost = bbr2_skb_marked_lost,
.undo_cwnd = bbr2_undo_cwnd,
.cwnd_event = bbr_cwnd_event,
.ssthresh = bbr2_ssthresh,
.tso_segs = bbr_tso_segs,
.get_info = bbr2_get_info,
.set_state = bbr2_set_state,
};
static int __init bbr_register(void)
{
BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&tcp_bbr2_cong_ops);
}
static void __exit bbr_unregister(void)
{
tcp_unregister_congestion_control(&tcp_bbr2_cong_ops);
}
module_init(bbr_register);
module_exit(bbr_unregister);
MODULE_AUTHOR("Van Jacobson <vanj@google.com>");
MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>");
MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>");
MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>");
MODULE_AUTHOR("Priyaranjan Jha <priyarjha@google.com>");
MODULE_AUTHOR("Yousuk Seung <ysseung@google.com>");
MODULE_AUTHOR("Kevin Yang <yyd@google.com>");
MODULE_AUTHOR("Arjun Roy <arjunroy@google.com>");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");