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/*
* ngtcp2
*
* Copyright (c) 2021 ngtcp2 contributors
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include "ngtcp2_bbr.h"
#include <assert.h>
#include <string.h>
#include "ngtcp2_log.h"
#include "ngtcp2_macro.h"
#include "ngtcp2_mem.h"
#include "ngtcp2_rcvry.h"
#include "ngtcp2_rst.h"
#include "ngtcp2_conn_stat.h"
#define NGTCP2_BBR_MAX_BW_FILTERLEN 2
#define NGTCP2_BBR_EXTRA_ACKED_FILTERLEN 10
#define NGTCP2_BBR_STARTUP_PACING_GAIN_H 277
#define NGTCP2_BBR_STARTUP_CWND_GAIN_H 200
#define NGTCP2_BBR_PROBE_RTT_CWND_GAIN_H 50
#define NGTCP2_BBR_BETA_NUMER 7
#define NGTCP2_BBR_BETA_DENOM 10
#define NGTCP2_BBR_LOSS_THRESH_NUMER 2
#define NGTCP2_BBR_LOSS_THRESH_DENOM 100
#define NGTCP2_BBR_HEADROOM_NUMER 15
#define NGTCP2_BBR_HEADROOM_DENOM 100
#define NGTCP2_BBR_PROBE_RTT_INTERVAL (5 * NGTCP2_SECONDS)
#define NGTCP2_BBR_MIN_RTT_FILTERLEN (10 * NGTCP2_SECONDS)
#define NGTCP2_BBR_PROBE_RTT_DURATION (200 * NGTCP2_MILLISECONDS)
#define NGTCP2_BBR_PACING_MARGIN_PERCENT 1
static void bbr_on_init(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp initial_ts);
static void bbr_on_transmit(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_reset_congestion_signals(ngtcp2_cc_bbr *bbr);
static void bbr_reset_lower_bounds(ngtcp2_cc_bbr *bbr);
static void bbr_init_round_counting(ngtcp2_cc_bbr *bbr);
static void bbr_init_full_pipe(ngtcp2_cc_bbr *bbr);
static void bbr_init_pacing_rate(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static void bbr_set_pacing_rate_with_gain(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
uint64_t pacing_gain_h);
static void bbr_set_pacing_rate(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static void bbr_enter_startup(ngtcp2_cc_bbr *bbr);
static void bbr_check_startup_done(ngtcp2_cc_bbr *bbr,
const ngtcp2_cc_ack *ack);
static void bbr_update_on_ack(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
static void bbr_update_model_and_state(ngtcp2_cc_bbr *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts);
static void bbr_update_control_parameters(ngtcp2_cc_bbr *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_update_on_loss(ngtcp2_cc_bbr *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts);
static void bbr_update_latest_delivery_signals(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_advance_latest_delivery_signals(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_update_congestion_signals(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_adapt_lower_bounds_from_congestion(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_init_lower_bounds(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static void bbr_loss_lower_bounds(ngtcp2_cc_bbr *bbr);
static void bbr_bound_bw_for_model(ngtcp2_cc_bbr *bbr);
static void bbr_update_max_bw(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_update_round(ngtcp2_cc_bbr *bbr, const ngtcp2_cc_ack *ack);
static void bbr_start_round(ngtcp2_cc_bbr *bbr);
static int bbr_is_in_probe_bw_state(ngtcp2_cc_bbr *bbr);
static void bbr_update_ack_aggregation(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts);
static void bbr_enter_drain(ngtcp2_cc_bbr *bbr);
static void bbr_check_drain(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_enter_probe_bw(ngtcp2_cc_bbr *bbr, ngtcp2_tstamp ts);
static void bbr_start_probe_bw_down(ngtcp2_cc_bbr *bbr, ngtcp2_tstamp ts);
static void bbr_start_probe_bw_cruise(ngtcp2_cc_bbr *bbr);
static void bbr_start_probe_bw_refill(ngtcp2_cc_bbr *bbr);
static void bbr_start_probe_bw_up(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_update_probe_bw_cycle_phase(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts);
static int bbr_check_time_to_cruise(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static int bbr_has_elapsed_in_phase(ngtcp2_cc_bbr *bbr,
ngtcp2_duration interval, ngtcp2_tstamp ts);
static uint64_t bbr_inflight_with_headroom(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_raise_inflight_hi_slope(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_probe_inflight_hi_upward(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_adapt_upper_bounds(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
static int bbr_check_time_to_probe_bw(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_pick_probe_wait(ngtcp2_cc_bbr *bbr);
static int bbr_is_reno_coexistence_probe_time(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static uint64_t bbr_target_inflight(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static int bbr_check_inflight_too_high(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static int is_inflight_too_high(const ngtcp2_rs *rs);
static void bbr_handle_inflight_too_high(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_rs *rs, ngtcp2_tstamp ts);
static void bbr_handle_lost_packet(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts);
static uint64_t bbr_inflight_hi_from_lost_packet(ngtcp2_cc_bbr *bbr,
const ngtcp2_rs *rs,
const ngtcp2_cc_pkt *pkt);
static void bbr_update_min_rtt(ngtcp2_cc_bbr *bbr, const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts);
static void bbr_check_probe_rtt(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_enter_probe_rtt(ngtcp2_cc_bbr *bbr);
static void bbr_handle_probe_rtt(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_check_probe_rtt_done(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat, ngtcp2_tstamp ts);
static void bbr_mark_connection_app_limited(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_exit_probe_rtt(ngtcp2_cc_bbr *bbr, ngtcp2_tstamp ts);
static void bbr_handle_restart_from_idle(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static uint64_t bbr_bdp_multiple(ngtcp2_cc_bbr *bbr, uint64_t bw,
uint64_t gain_h);
static uint64_t bbr_quantization_budget(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
uint64_t inflight);
static uint64_t bbr_inflight(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
uint64_t bw, uint64_t gain_h);
static void bbr_update_max_inflight(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_update_offload_budget(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static uint64_t min_pipe_cwnd(size_t max_udp_payload_size);
static void bbr_advance_max_bw_filter(ngtcp2_cc_bbr *bbr);
static void bbr_modulate_cwnd_for_recovery(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_save_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static void bbr_restore_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static uint64_t bbr_probe_rtt_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static void bbr_bound_cwnd_for_probe_rtt(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_set_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_bound_cwnd_for_model(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat);
static void bbr_set_send_quantum(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat);
static int in_congestion_recovery(const ngtcp2_conn_stat *cstat,
ngtcp2_tstamp sent_time);
static void bbr_handle_recovery(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
static void bbr_on_init(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp initial_ts) {
ngtcp2_window_filter_init(&bbr->max_bw_filter, NGTCP2_BBR_MAX_BW_FILTERLEN);
ngtcp2_window_filter_init(&bbr->extra_acked_filter,
NGTCP2_BBR_EXTRA_ACKED_FILTERLEN);
bbr->min_rtt = UINT64_MAX;
bbr->min_rtt_stamp = initial_ts;
/* remark: Use UINT64_MAX instead of 0 for consistency. */
bbr->probe_rtt_done_stamp = UINT64_MAX;
bbr->probe_rtt_round_done = 0;
bbr->prior_cwnd = 0;
bbr->idle_restart = 0;
bbr->extra_acked_interval_start = initial_ts;
bbr->extra_acked_delivered = 0;
bbr_reset_congestion_signals(bbr);
bbr_reset_lower_bounds(bbr);
bbr_init_round_counting(bbr);
bbr_init_full_pipe(bbr);
bbr_init_pacing_rate(bbr, cstat);
bbr_enter_startup(bbr);
cstat->send_quantum = cstat->max_tx_udp_payload_size * 10;
/* Missing in documentation */
bbr->loss_round_start = 0;
bbr->loss_round_delivered = UINT64_MAX;
bbr->rounds_since_bw_probe = 0;
bbr->max_bw = 0;
bbr->bw = 0;
bbr->cycle_count = 0;
bbr->extra_acked = 0;
bbr->bytes_lost_in_round = 0;
bbr->loss_events_in_round = 0;
bbr->offload_budget = 0;
bbr->probe_up_cnt = UINT64_MAX;
bbr->cycle_stamp = UINT64_MAX;
bbr->ack_phase = 0;
bbr->bw_probe_wait = 0;
bbr->bw_probe_samples = 0;
bbr->bw_probe_up_rounds = 0;
bbr->bw_probe_up_acks = 0;
bbr->inflight_hi = UINT64_MAX;
bbr->bw_hi = UINT64_MAX;
bbr->probe_rtt_expired = 0;
bbr->probe_rtt_min_delay = UINT64_MAX;
bbr->probe_rtt_min_stamp = initial_ts;
bbr->in_loss_recovery = 0;
bbr->packet_conservation = 0;
bbr->max_inflight = 0;
bbr->congestion_recovery_start_ts = UINT64_MAX;
bbr->congestion_recovery_next_round_delivered = 0;
bbr->prior_inflight_lo = 0;
bbr->prior_inflight_hi = 0;
bbr->prior_bw_lo = 0;
}
static void bbr_reset_congestion_signals(ngtcp2_cc_bbr *bbr) {
bbr->loss_in_round = 0;
bbr->bw_latest = 0;
bbr->inflight_latest = 0;
}
static void bbr_reset_lower_bounds(ngtcp2_cc_bbr *bbr) {
bbr->bw_lo = UINT64_MAX;
bbr->inflight_lo = UINT64_MAX;
}
static void bbr_init_round_counting(ngtcp2_cc_bbr *bbr) {
bbr->next_round_delivered = 0;
bbr->round_start = 0;
bbr->round_count = 0;
}
static void bbr_init_full_pipe(ngtcp2_cc_bbr *bbr) {
bbr->filled_pipe = 0;
bbr->full_bw = 0;
bbr->full_bw_count = 0;
}
static void bbr_check_startup_full_bandwidth(ngtcp2_cc_bbr *bbr) {
if (bbr->filled_pipe || !bbr->round_start || bbr->rst->rs.is_app_limited) {
return;
}
if (bbr->max_bw * 100 >= bbr->full_bw * 125) {
bbr->full_bw = bbr->max_bw;
bbr->full_bw_count = 0;
}
++bbr->full_bw_count;
if (bbr->full_bw_count >= 3) {
bbr->filled_pipe = 1;
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA,
"bbr filled pipe, full_bw=%" PRIu64, bbr->full_bw);
}
}
static void bbr_check_startup_high_loss(ngtcp2_cc_bbr *bbr,
const ngtcp2_cc_ack *ack) {
if (bbr->filled_pipe || !bbr->round_start || bbr->rst->rs.is_app_limited) {
return;
}
if (bbr->loss_events_in_round <= 3) {
return;
}
/* loss_thresh = 2% */
if (bbr->bytes_lost_in_round * 100 <= ack->prior_bytes_in_flight * 2) {
return;
}
bbr->filled_pipe = 1;
}
static void bbr_init_pacing_rate(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat) {
cstat->pacing_interval = NGTCP2_MILLISECONDS * 100 /
NGTCP2_BBR_STARTUP_PACING_GAIN_H / bbr->initial_cwnd;
}
static void bbr_set_pacing_rate_with_gain(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
uint64_t pacing_gain_h) {
ngtcp2_duration interval;
if (bbr->bw == 0) {
return;
}
interval = NGTCP2_SECONDS * 100 * 100 / pacing_gain_h / bbr->bw /
(100 - NGTCP2_BBR_PACING_MARGIN_PERCENT);
if (bbr->filled_pipe || interval < cstat->pacing_interval) {
cstat->pacing_interval = interval;
}
}
static void bbr_set_pacing_rate(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat) {
bbr_set_pacing_rate_with_gain(bbr, cstat, bbr->pacing_gain_h);
}
static void bbr_enter_startup(ngtcp2_cc_bbr *bbr) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA, "bbr enter Startup");
bbr->state = NGTCP2_BBR_STATE_STARTUP;
bbr->pacing_gain_h = NGTCP2_BBR_STARTUP_PACING_GAIN_H;
bbr->cwnd_gain_h = NGTCP2_BBR_STARTUP_CWND_GAIN_H;
}
static void bbr_check_startup_done(ngtcp2_cc_bbr *bbr,
const ngtcp2_cc_ack *ack) {
bbr_check_startup_full_bandwidth(bbr);
bbr_check_startup_high_loss(bbr, ack);
if (bbr->state == NGTCP2_BBR_STATE_STARTUP && bbr->filled_pipe) {
bbr_enter_drain(bbr);
}
}
static void bbr_on_transmit(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
bbr_handle_restart_from_idle(bbr, cstat, ts);
}
static void bbr_update_on_ack(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
bbr_update_model_and_state(bbr, cstat, ack, ts);
bbr_update_control_parameters(bbr, cstat, ack);
}
static void bbr_update_model_and_state(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts) {
bbr_update_latest_delivery_signals(bbr, cstat);
bbr_update_congestion_signals(bbr, cstat, ack);
bbr_update_ack_aggregation(bbr, cstat, ack, ts);
bbr_check_startup_done(bbr, ack);
bbr_check_drain(bbr, cstat, ts);
bbr_update_probe_bw_cycle_phase(bbr, cstat, ack, ts);
bbr_update_min_rtt(bbr, ack, ts);
bbr_check_probe_rtt(bbr, cstat, ts);
bbr_advance_latest_delivery_signals(bbr, cstat);
bbr_bound_bw_for_model(bbr);
}
static void bbr_update_control_parameters(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
bbr_set_pacing_rate(bbr, cstat);
bbr_set_send_quantum(bbr, cstat);
bbr_set_cwnd(bbr, cstat, ack);
}
static void bbr_update_on_loss(ngtcp2_cc_bbr *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
bbr_handle_lost_packet(cc, cstat, pkt, ts);
}
static void bbr_update_latest_delivery_signals(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
bbr->loss_round_start = 0;
bbr->bw_latest = ngtcp2_max(bbr->bw_latest, cstat->delivery_rate_sec);
bbr->inflight_latest =
ngtcp2_max(bbr->inflight_latest, bbr->rst->rs.delivered);
if (bbr->rst->rs.prior_delivered >= bbr->loss_round_delivered) {
bbr->loss_round_delivered = bbr->rst->delivered;
bbr->loss_round_start = 1;
}
}
static void bbr_advance_latest_delivery_signals(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
if (bbr->loss_round_start) {
bbr->bw_latest = cstat->delivery_rate_sec;
bbr->inflight_latest = bbr->rst->rs.delivered;
}
}
static void bbr_update_congestion_signals(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
bbr_update_max_bw(bbr, cstat, ack);
if (ack->bytes_lost) {
bbr->bytes_lost_in_round += ack->bytes_lost;
++bbr->loss_events_in_round;
if (!bbr->loss_in_round) {
bbr->loss_in_round = 1;
bbr->loss_round_delivered = bbr->rst->delivered;
}
}
if (!bbr->loss_round_start) {
return;
}
bbr_adapt_lower_bounds_from_congestion(bbr, cstat);
bbr->loss_in_round = 0;
}
static void bbr_adapt_lower_bounds_from_congestion(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
if (bbr_is_in_probe_bw_state(bbr)) {
return;
}
if (bbr->loss_in_round) {
bbr_init_lower_bounds(bbr, cstat);
bbr_loss_lower_bounds(bbr);
}
}
static void bbr_init_lower_bounds(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat) {
if (bbr->bw_lo == UINT64_MAX) {
bbr->bw_lo = bbr->max_bw;
}
if (bbr->inflight_lo == UINT64_MAX) {
bbr->inflight_lo = cstat->cwnd;
}
}
static void bbr_loss_lower_bounds(ngtcp2_cc_bbr *bbr) {
bbr->bw_lo = ngtcp2_max(bbr->bw_latest, bbr->bw_lo * NGTCP2_BBR_BETA_NUMER /
NGTCP2_BBR_BETA_DENOM);
bbr->inflight_lo = ngtcp2_max(bbr->inflight_latest,
bbr->inflight_lo * NGTCP2_BBR_BETA_NUMER /
NGTCP2_BBR_BETA_DENOM);
}
static void bbr_bound_bw_for_model(ngtcp2_cc_bbr *bbr) {
bbr->bw = ngtcp2_min(bbr->max_bw, bbr->bw_lo);
bbr->bw = ngtcp2_min(bbr->bw, bbr->bw_hi);
}
static void bbr_update_max_bw(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
bbr_update_round(bbr, ack);
if (cstat->delivery_rate_sec >= bbr->max_bw || !bbr->rst->rs.is_app_limited) {
ngtcp2_window_filter_update(&bbr->max_bw_filter, cstat->delivery_rate_sec,
bbr->cycle_count);
bbr->max_bw = ngtcp2_window_filter_get_best(&bbr->max_bw_filter);
}
}
static void bbr_update_round(ngtcp2_cc_bbr *bbr, const ngtcp2_cc_ack *ack) {
if (ack->pkt_delivered >= bbr->next_round_delivered) {
bbr_start_round(bbr);
++bbr->round_count;
++bbr->rounds_since_bw_probe;
bbr->round_start = 1;
bbr->bytes_lost_in_round = 0;
bbr->loss_events_in_round = 0;
bbr->rst->is_cwnd_limited = 0;
return;
}
bbr->round_start = 0;
}
static void bbr_start_round(ngtcp2_cc_bbr *bbr) {
bbr->next_round_delivered = bbr->rst->delivered;
}
static int bbr_is_in_probe_bw_state(ngtcp2_cc_bbr *bbr) {
switch (bbr->state) {
case NGTCP2_BBR_STATE_PROBE_BW_DOWN:
case NGTCP2_BBR_STATE_PROBE_BW_CRUISE:
case NGTCP2_BBR_STATE_PROBE_BW_REFILL:
case NGTCP2_BBR_STATE_PROBE_BW_UP:
return 1;
default:
return 0;
}
}
static void bbr_update_ack_aggregation(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts) {
ngtcp2_duration interval = ts - bbr->extra_acked_interval_start;
uint64_t expected_delivered = bbr->bw * interval / NGTCP2_SECONDS;
uint64_t extra;
if (bbr->extra_acked_delivered <= expected_delivered) {
bbr->extra_acked_delivered = 0;
bbr->extra_acked_interval_start = ts;
expected_delivered = 0;
}
bbr->extra_acked_delivered += ack->bytes_delivered;
extra = bbr->extra_acked_delivered - expected_delivered;
extra = ngtcp2_min(extra, cstat->cwnd);
ngtcp2_window_filter_update(&bbr->extra_acked_filter, extra,
bbr->round_count);
bbr->extra_acked = ngtcp2_window_filter_get_best(&bbr->extra_acked_filter);
}
static void bbr_enter_drain(ngtcp2_cc_bbr *bbr) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA, "bbr enter Drain");
bbr->state = NGTCP2_BBR_STATE_DRAIN;
bbr->pacing_gain_h = 100 * 100 / NGTCP2_BBR_STARTUP_CWND_GAIN_H;
bbr->cwnd_gain_h = NGTCP2_BBR_STARTUP_CWND_GAIN_H;
}
static void bbr_check_drain(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (bbr->state == NGTCP2_BBR_STATE_DRAIN &&
cstat->bytes_in_flight <= bbr_inflight(bbr, cstat, bbr->bw, 100)) {
bbr_enter_probe_bw(bbr, ts);
}
}
static void bbr_enter_probe_bw(ngtcp2_cc_bbr *bbr, ngtcp2_tstamp ts) {
bbr_start_probe_bw_down(bbr, ts);
}
static void bbr_start_probe_bw_down(ngtcp2_cc_bbr *bbr, ngtcp2_tstamp ts) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA, "bbr start ProbeBW_DOWN");
bbr_reset_congestion_signals(bbr);
bbr->probe_up_cnt = UINT64_MAX;
bbr_pick_probe_wait(bbr);
bbr->cycle_stamp = ts;
bbr->ack_phase = NGTCP2_BBR_ACK_PHASE_ACKS_PROBE_STOPPING;
bbr_start_round(bbr);
bbr->state = NGTCP2_BBR_STATE_PROBE_BW_DOWN;
bbr->pacing_gain_h = 90;
bbr->cwnd_gain_h = 200;
}
static void bbr_start_probe_bw_cruise(ngtcp2_cc_bbr *bbr) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA,
"bbr start ProbeBW_CRUISE");
bbr->state = NGTCP2_BBR_STATE_PROBE_BW_CRUISE;
bbr->pacing_gain_h = 100;
bbr->cwnd_gain_h = 200;
}
static void bbr_start_probe_bw_refill(ngtcp2_cc_bbr *bbr) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA,
"bbr start ProbeBW_REFILL");
bbr_reset_lower_bounds(bbr);
bbr->bw_probe_up_rounds = 0;
bbr->bw_probe_up_acks = 0;
bbr->ack_phase = NGTCP2_BBR_ACK_PHASE_ACKS_REFILLING;
bbr_start_round(bbr);
bbr->state = NGTCP2_BBR_STATE_PROBE_BW_REFILL;
bbr->pacing_gain_h = 100;
bbr->cwnd_gain_h = 200;
}
static void bbr_start_probe_bw_up(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA, "bbr start ProbeBW_UP");
bbr->ack_phase = NGTCP2_BBR_ACK_PHASE_ACKS_PROBE_STARTING;
bbr_start_round(bbr);
bbr->cycle_stamp = ts;
bbr->state = NGTCP2_BBR_STATE_PROBE_BW_UP;
bbr->pacing_gain_h = 125;
bbr->cwnd_gain_h = 225;
bbr_raise_inflight_hi_slope(bbr, cstat);
}
static void bbr_update_probe_bw_cycle_phase(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts) {
if (!bbr->filled_pipe) {
return;
}
bbr_adapt_upper_bounds(bbr, cstat, ack, ts);
if (!bbr_is_in_probe_bw_state(bbr)) {
return;
}
switch (bbr->state) {
case NGTCP2_BBR_STATE_PROBE_BW_DOWN:
if (bbr_check_time_to_probe_bw(bbr, cstat, ts)) {
return;
}
if (bbr_check_time_to_cruise(bbr, cstat, ts)) {
bbr_start_probe_bw_cruise(bbr);
}
break;
case NGTCP2_BBR_STATE_PROBE_BW_CRUISE:
if (bbr_check_time_to_probe_bw(bbr, cstat, ts)) {
return;
}
break;
case NGTCP2_BBR_STATE_PROBE_BW_REFILL:
if (bbr->round_start) {
bbr->bw_probe_samples = 1;
bbr_start_probe_bw_up(bbr, cstat, ts);
}
break;
case NGTCP2_BBR_STATE_PROBE_BW_UP:
if (bbr_has_elapsed_in_phase(bbr, bbr->min_rtt, ts) &&
cstat->bytes_in_flight > bbr_inflight(bbr, cstat, bbr->max_bw, 125)) {
bbr_start_probe_bw_down(bbr, ts);
}
break;
default:
break;
}
}
static int bbr_check_time_to_cruise(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
(void)ts;
if (cstat->bytes_in_flight > bbr_inflight_with_headroom(bbr, cstat)) {
return 0;
}
if (cstat->bytes_in_flight <= bbr_inflight(bbr, cstat, bbr->max_bw, 100)) {
return 1;
}
return 0;
}
static int bbr_has_elapsed_in_phase(ngtcp2_cc_bbr *bbr,
ngtcp2_duration interval,
ngtcp2_tstamp ts) {
return ts > bbr->cycle_stamp + interval;
}
static uint64_t bbr_inflight_with_headroom(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t headroom;
uint64_t mpcwnd;
if (bbr->inflight_hi == UINT64_MAX) {
return UINT64_MAX;
}
headroom = ngtcp2_max(cstat->max_tx_udp_payload_size,
bbr->inflight_hi * NGTCP2_BBR_HEADROOM_NUMER /
NGTCP2_BBR_HEADROOM_DENOM);
mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
if (bbr->inflight_hi > headroom) {
return ngtcp2_max(bbr->inflight_hi - headroom, mpcwnd);
}
return mpcwnd;
}
static void bbr_raise_inflight_hi_slope(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t growth_this_round = cstat->max_tx_udp_payload_size
<< bbr->bw_probe_up_rounds;
bbr->bw_probe_up_rounds = ngtcp2_min(bbr->bw_probe_up_rounds + 1, 30);
bbr->probe_up_cnt = ngtcp2_max(cstat->cwnd / growth_this_round, 1) *
cstat->max_tx_udp_payload_size;
}
static void bbr_probe_inflight_hi_upward(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
uint64_t delta;
if (!bbr->rst->is_cwnd_limited || cstat->cwnd < bbr->inflight_hi) {
return;
}
bbr->bw_probe_up_acks += ack->bytes_delivered;
if (bbr->bw_probe_up_acks >= bbr->probe_up_cnt) {
delta = bbr->bw_probe_up_acks / bbr->probe_up_cnt;
bbr->bw_probe_up_acks -= delta * bbr->probe_up_cnt;
bbr->inflight_hi += delta * cstat->max_tx_udp_payload_size;
}
if (bbr->round_start) {
bbr_raise_inflight_hi_slope(bbr, cstat);
}
}
static void bbr_adapt_upper_bounds(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
if (bbr->ack_phase == NGTCP2_BBR_ACK_PHASE_ACKS_PROBE_STARTING &&
bbr->round_start) {
bbr->ack_phase = NGTCP2_BBR_ACK_PHASE_ACKS_PROBE_FEEDBACK;
}
if (bbr->ack_phase == NGTCP2_BBR_ACK_PHASE_ACKS_PROBE_STOPPING &&
bbr->round_start) {
if (bbr_is_in_probe_bw_state(bbr) && !bbr->rst->rs.is_app_limited) {
bbr_advance_max_bw_filter(bbr);
}
}
if (!bbr_check_inflight_too_high(bbr, cstat, ts)) {
/* bbr->bw_hi never be updated */
if (bbr->inflight_hi == UINT64_MAX /* || bbr->bw_hi == UINT64_MAX */) {
return;
}
if (bbr->rst->rs.tx_in_flight > bbr->inflight_hi) {
bbr->inflight_hi = bbr->rst->rs.tx_in_flight;
}
if (cstat->delivery_rate_sec > bbr->bw_hi) {
bbr->bw_hi = cstat->delivery_rate_sec;
}
if (bbr->state == NGTCP2_BBR_STATE_PROBE_BW_UP) {
bbr_probe_inflight_hi_upward(bbr, cstat, ack);
}
}
}
static int bbr_check_time_to_probe_bw(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (bbr_has_elapsed_in_phase(bbr, bbr->bw_probe_wait, ts) ||
bbr_is_reno_coexistence_probe_time(bbr, cstat)) {
bbr_start_probe_bw_refill(bbr);
return 1;
}
return 0;
}
static void bbr_pick_probe_wait(ngtcp2_cc_bbr *bbr) {
uint8_t rand;
bbr->rand(&rand, 1, &bbr->rand_ctx);
bbr->rounds_since_bw_probe = (uint64_t)(rand * 2 / 256);
bbr->rand(&rand, 1, &bbr->rand_ctx);
bbr->bw_probe_wait =
2 * NGTCP2_SECONDS + (ngtcp2_tstamp)(NGTCP2_SECONDS * rand / 255);
}
static int bbr_is_reno_coexistence_probe_time(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t reno_rounds =
bbr_target_inflight(bbr, cstat) / cstat->max_tx_udp_payload_size;
return bbr->rounds_since_bw_probe >= ngtcp2_min(reno_rounds, 63);
}
static uint64_t bbr_target_inflight(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t bdp = bbr_inflight(bbr, cstat, bbr->bw, 100);
return ngtcp2_min(bdp, cstat->cwnd);
}
static int bbr_check_inflight_too_high(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (is_inflight_too_high(&bbr->rst->rs)) {
if (bbr->bw_probe_samples) {
bbr_handle_inflight_too_high(bbr, cstat, &bbr->rst->rs, ts);
}
return 1;
}
return 0;
}
static int is_inflight_too_high(const ngtcp2_rs *rs) {
return rs->lost * NGTCP2_BBR_LOSS_THRESH_DENOM >
rs->tx_in_flight * NGTCP2_BBR_LOSS_THRESH_NUMER;
}
static void bbr_handle_inflight_too_high(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_rs *rs,
ngtcp2_tstamp ts) {
bbr->bw_probe_samples = 0;
if (!rs->is_app_limited) {
bbr->inflight_hi = ngtcp2_max(
rs->tx_in_flight, bbr_target_inflight(bbr, cstat) *
NGTCP2_BBR_BETA_NUMER / NGTCP2_BBR_BETA_DENOM);
}
if (bbr->state == NGTCP2_BBR_STATE_PROBE_BW_UP) {
bbr_start_probe_bw_down(bbr, ts);
}
}
static void bbr_handle_lost_packet(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
ngtcp2_rs rs = {0};
if (!bbr->bw_probe_samples) {
return;
}
rs.tx_in_flight = pkt->tx_in_flight;
/* bbr->rst->lost is not incremented for pkt yet */
rs.lost = bbr->rst->lost + pkt->pktlen - pkt->lost;
rs.is_app_limited = pkt->is_app_limited;
if (is_inflight_too_high(&rs)) {
rs.tx_in_flight = bbr_inflight_hi_from_lost_packet(bbr, &rs, pkt);
bbr_handle_inflight_too_high(bbr, cstat, &rs, ts);
}
}
static uint64_t bbr_inflight_hi_from_lost_packet(ngtcp2_cc_bbr *bbr,
const ngtcp2_rs *rs,
const ngtcp2_cc_pkt *pkt) {
uint64_t inflight_prev, lost_prev, lost_prefix;
(void)bbr;
assert(rs->tx_in_flight >= pkt->pktlen);
inflight_prev = rs->tx_in_flight - pkt->pktlen;
assert(rs->lost >= pkt->pktlen);
lost_prev = rs->lost - pkt->pktlen;
if (inflight_prev * NGTCP2_BBR_LOSS_THRESH_NUMER <
lost_prev * NGTCP2_BBR_LOSS_THRESH_DENOM) {
return inflight_prev;
}
lost_prefix = (inflight_prev * NGTCP2_BBR_LOSS_THRESH_NUMER -
lost_prev * NGTCP2_BBR_LOSS_THRESH_DENOM) /
(NGTCP2_BBR_LOSS_THRESH_DENOM - NGTCP2_BBR_LOSS_THRESH_NUMER);
return inflight_prev + lost_prefix;
}
static void bbr_update_min_rtt(ngtcp2_cc_bbr *bbr, const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts) {
int min_rtt_expired;
bbr->probe_rtt_expired =
ts > bbr->probe_rtt_min_stamp + NGTCP2_BBR_PROBE_RTT_INTERVAL;
if (ack->rtt != UINT64_MAX &&
(ack->rtt < bbr->probe_rtt_min_delay || bbr->probe_rtt_expired)) {
bbr->probe_rtt_min_delay = ack->rtt;
bbr->probe_rtt_min_stamp = ts;
}
min_rtt_expired = ts > bbr->min_rtt_stamp + NGTCP2_BBR_MIN_RTT_FILTERLEN;
if (bbr->probe_rtt_min_delay < bbr->min_rtt || min_rtt_expired) {
bbr->min_rtt = bbr->probe_rtt_min_delay;
bbr->min_rtt_stamp = bbr->probe_rtt_min_stamp;
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA,
"bbr update min_rtt=%" PRIu64, bbr->min_rtt);
}
}
static void bbr_check_probe_rtt(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (bbr->state != NGTCP2_BBR_STATE_PROBE_RTT && bbr->probe_rtt_expired &&
!bbr->idle_restart) {
bbr_enter_probe_rtt(bbr);
bbr_save_cwnd(bbr, cstat);
bbr->probe_rtt_done_stamp = UINT64_MAX;
bbr->ack_phase = NGTCP2_BBR_ACK_PHASE_ACKS_PROBE_STOPPING;
bbr_start_round(bbr);
}
if (bbr->state == NGTCP2_BBR_STATE_PROBE_RTT) {
bbr_handle_probe_rtt(bbr, cstat, ts);
}
if (bbr->rst->rs.delivered) {
bbr->idle_restart = 0;
}
}
static void bbr_enter_probe_rtt(ngtcp2_cc_bbr *bbr) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA, "bbr enter ProbeRTT");
bbr->state = NGTCP2_BBR_STATE_PROBE_RTT;
bbr->pacing_gain_h = 100;
bbr->cwnd_gain_h = NGTCP2_BBR_PROBE_RTT_CWND_GAIN_H;
}
static void bbr_handle_probe_rtt(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
bbr_mark_connection_app_limited(bbr, cstat);
if (bbr->probe_rtt_done_stamp == UINT64_MAX &&
cstat->bytes_in_flight <= bbr_probe_rtt_cwnd(bbr, cstat)) {
bbr->probe_rtt_done_stamp = ts + NGTCP2_BBR_PROBE_RTT_DURATION;
bbr->probe_rtt_round_done = 0;
bbr_start_round(bbr);
return;
}
if (bbr->probe_rtt_done_stamp != UINT64_MAX) {
if (bbr->round_start) {
bbr->probe_rtt_round_done = 1;
}
if (bbr->probe_rtt_round_done) {
bbr_check_probe_rtt_done(bbr, cstat, ts);
}
}
}
static void bbr_check_probe_rtt_done(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (bbr->probe_rtt_done_stamp != UINT64_MAX &&
ts > bbr->probe_rtt_done_stamp) {
bbr->probe_rtt_min_stamp = ts;
bbr_restore_cwnd(bbr, cstat);
bbr_exit_probe_rtt(bbr, ts);
}
}
static void bbr_mark_connection_app_limited(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t app_limited = bbr->rst->delivered + cstat->bytes_in_flight;
if (app_limited) {
bbr->rst->app_limited = app_limited;
} else {
bbr->rst->app_limited = cstat->max_tx_udp_payload_size;
}
}
static void bbr_exit_probe_rtt(ngtcp2_cc_bbr *bbr, ngtcp2_tstamp ts) {
bbr_reset_lower_bounds(bbr);
if (bbr->filled_pipe) {
bbr_start_probe_bw_down(bbr, ts);
bbr_start_probe_bw_cruise(bbr);
} else {
bbr_enter_startup(bbr);
}
}
static void bbr_handle_restart_from_idle(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (cstat->bytes_in_flight == 0 && bbr->rst->app_limited) {
ngtcp2_log_info(bbr->cc.log, NGTCP2_LOG_EVENT_CCA, "bbr restart from idle");
bbr->idle_restart = 1;
bbr->extra_acked_interval_start = ts;
if (bbr_is_in_probe_bw_state(bbr)) {
bbr_set_pacing_rate_with_gain(bbr, cstat, 100);
} else if (bbr->state == NGTCP2_BBR_STATE_PROBE_RTT) {
bbr_check_probe_rtt_done(bbr, cstat, ts);
}
}
}
static uint64_t bbr_bdp_multiple(ngtcp2_cc_bbr *bbr, uint64_t bw,
uint64_t gain_h) {
uint64_t bdp;
if (bbr->min_rtt == UINT64_MAX) {
return bbr->initial_cwnd;
}
bdp = bw * bbr->min_rtt / NGTCP2_SECONDS;
return (uint64_t)(bdp * gain_h / 100);
}
static uint64_t min_pipe_cwnd(size_t max_udp_payload_size) {
return max_udp_payload_size * 4;
}
static uint64_t bbr_quantization_budget(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
uint64_t inflight) {
bbr_update_offload_budget(bbr, cstat);
inflight = ngtcp2_max(inflight, bbr->offload_budget);
inflight =
ngtcp2_max(inflight, min_pipe_cwnd(cstat->max_tx_udp_payload_size));
if (bbr->state == NGTCP2_BBR_STATE_PROBE_BW_UP) {
inflight += 2 * cstat->max_tx_udp_payload_size;
}
return inflight;
}
static uint64_t bbr_inflight(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
uint64_t bw, uint64_t gain_h) {
uint64_t inflight = bbr_bdp_multiple(bbr, bw, gain_h);
return bbr_quantization_budget(bbr, cstat, inflight);
}
static void bbr_update_max_inflight(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t inflight;
/* Not documented */
/* bbr_update_aggregation_budget(bbr); */
inflight =
bbr_bdp_multiple(bbr, bbr->bw, bbr->cwnd_gain_h) + bbr->extra_acked;
bbr->max_inflight = bbr_quantization_budget(bbr, cstat, inflight);
}
static void bbr_update_offload_budget(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
bbr->offload_budget = 3 * cstat->send_quantum;
}
static void bbr_advance_max_bw_filter(ngtcp2_cc_bbr *bbr) {
++bbr->cycle_count;
}
static void bbr_modulate_cwnd_for_recovery(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
if (ack->bytes_lost > 0) {
if (cstat->cwnd > ack->bytes_lost) {
cstat->cwnd -= ack->bytes_lost;
cstat->cwnd = ngtcp2_max(cstat->cwnd, 2 * cstat->max_tx_udp_payload_size);
} else {
cstat->cwnd = 2 * cstat->max_tx_udp_payload_size;
}
}
if (bbr->packet_conservation) {
cstat->cwnd =
ngtcp2_max(cstat->cwnd, cstat->bytes_in_flight + ack->bytes_delivered);
}
}
static void bbr_save_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat) {
if (!bbr->in_loss_recovery && bbr->state != NGTCP2_BBR_STATE_PROBE_RTT) {
bbr->prior_cwnd = cstat->cwnd;
return;
}
bbr->prior_cwnd = ngtcp2_max(bbr->prior_cwnd, cstat->cwnd);
}
static void bbr_restore_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat) {
cstat->cwnd = ngtcp2_max(cstat->cwnd, bbr->prior_cwnd);
}
static uint64_t bbr_probe_rtt_cwnd(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t probe_rtt_cwnd =
bbr_bdp_multiple(bbr, bbr->bw, NGTCP2_BBR_PROBE_RTT_CWND_GAIN_H);
uint64_t mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
return ngtcp2_max(probe_rtt_cwnd, mpcwnd);
}
static void bbr_bound_cwnd_for_probe_rtt(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t probe_rtt_cwnd;
if (bbr->state == NGTCP2_BBR_STATE_PROBE_RTT) {
probe_rtt_cwnd = bbr_probe_rtt_cwnd(bbr, cstat);
cstat->cwnd = ngtcp2_min(cstat->cwnd, probe_rtt_cwnd);
}
}
static void bbr_set_cwnd(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
uint64_t mpcwnd;
bbr_update_max_inflight(bbr, cstat);
bbr_modulate_cwnd_for_recovery(bbr, cstat, ack);
if (!bbr->packet_conservation) {
if (bbr->filled_pipe) {
cstat->cwnd += ack->bytes_delivered;
cstat->cwnd = ngtcp2_min(cstat->cwnd, bbr->max_inflight);
} else if (cstat->cwnd < bbr->max_inflight ||
bbr->rst->delivered < bbr->initial_cwnd) {
cstat->cwnd += ack->bytes_delivered;
}
mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
cstat->cwnd = ngtcp2_max(cstat->cwnd, mpcwnd);
}
bbr_bound_cwnd_for_probe_rtt(bbr, cstat);
bbr_bound_cwnd_for_model(bbr, cstat);
}
static void bbr_bound_cwnd_for_model(ngtcp2_cc_bbr *bbr,
ngtcp2_conn_stat *cstat) {
uint64_t cap = UINT64_MAX;
uint64_t mpcwnd = min_pipe_cwnd(cstat->max_tx_udp_payload_size);
if (bbr_is_in_probe_bw_state(bbr) &&
bbr->state != NGTCP2_BBR_STATE_PROBE_BW_CRUISE) {
cap = bbr->inflight_hi;
} else if (bbr->state == NGTCP2_BBR_STATE_PROBE_RTT ||
bbr->state == NGTCP2_BBR_STATE_PROBE_BW_CRUISE) {
cap = bbr_inflight_with_headroom(bbr, cstat);
}
cap = ngtcp2_min(cap, bbr->inflight_lo);
cap = ngtcp2_max(cap, mpcwnd);
cstat->cwnd = ngtcp2_min(cstat->cwnd, cap);
}
static void bbr_set_send_quantum(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat) {
size_t floor, send_quantum;
(void)bbr;
if (cstat->pacing_interval > (NGTCP2_SECONDS * 8 * 10 / 12) >> 20) {
floor = cstat->max_tx_udp_payload_size;
} else {
floor = 2 * cstat->max_tx_udp_payload_size;
}
if (cstat->pacing_interval) {
send_quantum = (size_t)(NGTCP2_MILLISECONDS / cstat->pacing_interval);
send_quantum = ngtcp2_min(send_quantum, 64 * 1024);
} else {
send_quantum = 64 * 1024;
}
cstat->send_quantum = ngtcp2_max(send_quantum, floor);
}
static int in_congestion_recovery(const ngtcp2_conn_stat *cstat,
ngtcp2_tstamp sent_time) {
return cstat->congestion_recovery_start_ts != UINT64_MAX &&
sent_time <= cstat->congestion_recovery_start_ts;
}
static void bbr_handle_recovery(ngtcp2_cc_bbr *bbr, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
if (bbr->in_loss_recovery) {
if (ts - cstat->congestion_recovery_start_ts >= cstat->smoothed_rtt) {
bbr->packet_conservation = 0;
}
if (ack->largest_pkt_sent_ts != UINT64_MAX &&
!in_congestion_recovery(cstat, ack->largest_pkt_sent_ts)) {
bbr->in_loss_recovery = 0;
bbr->packet_conservation = 0;
bbr_restore_cwnd(bbr, cstat);
}
return;
}
if (bbr->congestion_recovery_start_ts != UINT64_MAX) {
bbr->in_loss_recovery = 1;
bbr_save_cwnd(bbr, cstat);
cstat->cwnd =
cstat->bytes_in_flight +
ngtcp2_max(ack->bytes_delivered, cstat->max_tx_udp_payload_size);
cstat->congestion_recovery_start_ts = bbr->congestion_recovery_start_ts;
bbr->congestion_recovery_start_ts = UINT64_MAX;
bbr->packet_conservation = 1;
bbr->congestion_recovery_next_round_delivered = bbr->rst->delivered;
bbr->prior_inflight_hi = bbr->inflight_hi;
bbr->prior_inflight_lo = bbr->inflight_lo;
bbr->prior_bw_lo = bbr->bw_lo;
}
}
static void bbr_cc_on_pkt_lost(ngtcp2_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
bbr_update_on_loss(bbr, cstat, pkt, ts);
}
static void bbr_cc_congestion_event(ngtcp2_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp sent_ts, ngtcp2_tstamp ts) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
if (bbr->in_loss_recovery ||
bbr->congestion_recovery_start_ts != UINT64_MAX ||
in_congestion_recovery(cstat, sent_ts)) {
return;
}
bbr->congestion_recovery_start_ts = ts;
}
static void bbr_cc_on_spurious_congestion(ngtcp2_cc *cc,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
(void)ts;
bbr->congestion_recovery_start_ts = UINT64_MAX;
cstat->congestion_recovery_start_ts = UINT64_MAX;
if (bbr->in_loss_recovery) {
bbr->in_loss_recovery = 0;
bbr->packet_conservation = 0;
bbr_restore_cwnd(bbr, cstat);
bbr->full_bw_count = 0;
bbr->loss_in_round = 0;
bbr->inflight_lo = ngtcp2_max(bbr->inflight_lo, bbr->prior_inflight_lo);
bbr->inflight_hi = ngtcp2_max(bbr->inflight_hi, bbr->prior_inflight_hi);
bbr->bw_lo = ngtcp2_max(bbr->bw_lo, bbr->prior_bw_lo);
}
}
static void bbr_cc_on_persistent_congestion(ngtcp2_cc *cc,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
(void)ts;
cstat->congestion_recovery_start_ts = UINT64_MAX;
bbr->congestion_recovery_start_ts = UINT64_MAX;
bbr->in_loss_recovery = 0;
bbr->packet_conservation = 0;
bbr_save_cwnd(bbr, cstat);
cstat->cwnd = cstat->bytes_in_flight + cstat->max_tx_udp_payload_size;
cstat->cwnd =
ngtcp2_max(cstat->cwnd, min_pipe_cwnd(cstat->max_tx_udp_payload_size));
}
static void bbr_cc_on_ack_recv(ngtcp2_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
bbr_handle_recovery(bbr, cstat, ack, ts);
bbr_update_on_ack(bbr, cstat, ack, ts);
}
static void bbr_cc_on_pkt_sent(ngtcp2_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
bbr_on_transmit(bbr, cstat, pkt->sent_ts);
}
static void bbr_cc_reset(ngtcp2_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_cc_bbr *bbr = ngtcp2_struct_of(cc, ngtcp2_cc_bbr, cc);
bbr_on_init(bbr, cstat, ts);
}
void ngtcp2_cc_bbr_init(ngtcp2_cc_bbr *bbr, ngtcp2_log *log,
ngtcp2_conn_stat *cstat, ngtcp2_rst *rst,
ngtcp2_tstamp initial_ts, ngtcp2_rand rand,
const ngtcp2_rand_ctx *rand_ctx) {
memset(bbr, 0, sizeof(*bbr));
bbr->cc.log = log;
bbr->cc.on_pkt_lost = bbr_cc_on_pkt_lost;
bbr->cc.congestion_event = bbr_cc_congestion_event;
bbr->cc.on_spurious_congestion = bbr_cc_on_spurious_congestion;
bbr->cc.on_persistent_congestion = bbr_cc_on_persistent_congestion;
bbr->cc.on_ack_recv = bbr_cc_on_ack_recv;
bbr->cc.on_pkt_sent = bbr_cc_on_pkt_sent;
bbr->cc.reset = bbr_cc_reset;
bbr->rst = rst;
bbr->rand = rand;
bbr->rand_ctx = *rand_ctx;
bbr->initial_cwnd = cstat->cwnd;
bbr_on_init(bbr, cstat, initial_ts);
}
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