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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 "ngtcp2_log.h"
#include "ngtcp2_macro.h"
#include "ngtcp2_mem.h"
#include "ngtcp2_rcvry.h"
#include "ngtcp2_rst.h"
static const double pacing_gain_cycle[] = {1.25, 0.75, 1, 1, 1, 1, 1, 1};
#define NGTCP2_BBR_GAIN_CYCLELEN \
(sizeof(pacing_gain_cycle) / sizeof(pacing_gain_cycle[0]))
#define NGTCP2_BBR_HIGH_GAIN 2.89
#define NGTCP2_BBR_PROBE_RTT_DURATION (200 * NGTCP2_MILLISECONDS)
#define NGTCP2_RTPROP_FILTERLEN (10 * NGTCP2_SECONDS)
#define NGTCP2_BBR_BTL_BW_FILTERLEN 10
static void bbr_update_on_ack(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
static void bbr_update_model_and_state(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts);
static void bbr_update_control_parameters(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_on_transmit(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_init_round_counting(ngtcp2_bbr_cc *cc);
static void bbr_update_round(ngtcp2_bbr_cc *cc, const ngtcp2_cc_ack *ack);
static void bbr_update_btl_bw(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_update_rtprop(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_init_pacing_rate(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_set_pacing_rate_with_gain(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
double pacing_gain);
static void bbr_set_pacing_rate(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_set_send_quantum(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_update_target_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_modulate_cwnd_for_recovery(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_save_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_restore_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat);
static void bbr_modulate_cwnd_for_probe_rtt(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat);
static void bbr_set_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack);
static void bbr_init(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp initial_ts);
static void bbr_enter_startup(ngtcp2_bbr_cc *cc);
static void bbr_init_full_pipe(ngtcp2_bbr_cc *cc);
static void bbr_check_full_pipe(ngtcp2_bbr_cc *cc);
static void bbr_enter_drain(ngtcp2_bbr_cc *cc);
static void bbr_check_drain(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_enter_probe_bw(ngtcp2_bbr_cc *cc, ngtcp2_tstamp ts);
static void bbr_check_cycle_phase(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
static void bbr_advance_cycle_phase(ngtcp2_bbr_cc *cc, ngtcp2_tstamp ts);
static int bbr_is_next_cycle_phase(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts);
static void bbr_handle_restart_from_idle(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat);
static void bbr_check_probe_rtt(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_enter_probe_rtt(ngtcp2_bbr_cc *cc);
static void bbr_handle_probe_rtt(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts);
static void bbr_exit_probe_rtt(ngtcp2_bbr_cc *cc, ngtcp2_tstamp ts);
void ngtcp2_bbr_cc_init(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_rst *rst, ngtcp2_tstamp initial_ts,
ngtcp2_rand rand, const ngtcp2_rand_ctx *rand_ctx,
ngtcp2_log *log) {
cc->ccb.log = log;
cc->rst = rst;
cc->rand = rand;
cc->rand_ctx = *rand_ctx;
cc->initial_cwnd = cstat->cwnd;
bbr_init(cc, cstat, initial_ts);
}
void ngtcp2_bbr_cc_free(ngtcp2_bbr_cc *cc) { (void)cc; }
int ngtcp2_cc_bbr_cc_init(ngtcp2_cc *cc, ngtcp2_log *log,
ngtcp2_conn_stat *cstat, ngtcp2_rst *rst,
ngtcp2_tstamp initial_ts, ngtcp2_rand rand,
const ngtcp2_rand_ctx *rand_ctx,
const ngtcp2_mem *mem) {
ngtcp2_bbr_cc *bbr_cc;
bbr_cc = ngtcp2_mem_calloc(mem, 1, sizeof(ngtcp2_bbr_cc));
if (bbr_cc == NULL) {
return NGTCP2_ERR_NOMEM;
}
ngtcp2_bbr_cc_init(bbr_cc, cstat, rst, initial_ts, rand, rand_ctx, log);
cc->ccb = &bbr_cc->ccb;
cc->on_pkt_acked = ngtcp2_cc_bbr_cc_on_pkt_acked;
cc->congestion_event = ngtcp2_cc_bbr_cc_congestion_event;
cc->on_spurious_congestion = ngtcp2_cc_bbr_cc_on_spurious_congestion;
cc->on_persistent_congestion = ngtcp2_cc_bbr_cc_on_persistent_congestion;
cc->on_ack_recv = ngtcp2_cc_bbr_cc_on_ack_recv;
cc->on_pkt_sent = ngtcp2_cc_bbr_cc_on_pkt_sent;
cc->new_rtt_sample = ngtcp2_cc_bbr_cc_new_rtt_sample;
cc->reset = ngtcp2_cc_bbr_cc_reset;
cc->event = ngtcp2_cc_bbr_cc_event;
return 0;
}
void ngtcp2_cc_bbr_cc_free(ngtcp2_cc *cc, const ngtcp2_mem *mem) {
ngtcp2_bbr_cc *bbr_cc = ngtcp2_struct_of(cc->ccb, ngtcp2_bbr_cc, ccb);
ngtcp2_bbr_cc_free(bbr_cc);
ngtcp2_mem_free(mem, bbr_cc);
}
void ngtcp2_cc_bbr_cc_on_pkt_acked(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt, ngtcp2_tstamp ts) {
(void)ccx;
(void)cstat;
(void)pkt;
(void)ts;
}
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;
}
void ngtcp2_cc_bbr_cc_congestion_event(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp sent_ts,
ngtcp2_tstamp ts) {
ngtcp2_bbr_cc *cc = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr_cc, ccb);
if (cc->in_loss_recovery || cc->congestion_recovery_start_ts != UINT64_MAX ||
in_congestion_recovery(cstat, sent_ts)) {
return;
}
cc->congestion_recovery_start_ts = ts;
}
void ngtcp2_cc_bbr_cc_on_spurious_congestion(ngtcp2_cc *ccx,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_bbr_cc *cc = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr_cc, ccb);
(void)ts;
cc->congestion_recovery_start_ts = UINT64_MAX;
cstat->congestion_recovery_start_ts = UINT64_MAX;
if (cc->in_loss_recovery) {
cc->in_loss_recovery = 0;
cc->packet_conservation = 0;
bbr_restore_cwnd(cc, cstat);
}
}
void ngtcp2_cc_bbr_cc_on_persistent_congestion(ngtcp2_cc *ccx,
ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_bbr_cc *cc = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr_cc, ccb);
(void)ts;
cstat->congestion_recovery_start_ts = UINT64_MAX;
cc->congestion_recovery_start_ts = UINT64_MAX;
cc->in_loss_recovery = 0;
cc->packet_conservation = 0;
bbr_save_cwnd(cc, cstat);
cstat->cwnd = 2 * cstat->max_udp_payload_size;
}
void ngtcp2_cc_bbr_cc_on_ack_recv(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
ngtcp2_bbr_cc *bbr_cc = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr_cc, ccb);
bbr_update_on_ack(bbr_cc, cstat, ack, ts);
}
void ngtcp2_cc_bbr_cc_on_pkt_sent(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_pkt *pkt) {
ngtcp2_bbr_cc *bbr_cc = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr_cc, ccb);
(void)pkt;
bbr_on_transmit(bbr_cc, cstat);
}
void ngtcp2_cc_bbr_cc_new_rtt_sample(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
(void)ccx;
(void)cstat;
(void)ts;
}
void ngtcp2_cc_bbr_cc_reset(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
ngtcp2_bbr_cc *bbr_cc = ngtcp2_struct_of(ccx->ccb, ngtcp2_bbr_cc, ccb);
bbr_init(bbr_cc, cstat, ts);
}
void ngtcp2_cc_bbr_cc_event(ngtcp2_cc *ccx, ngtcp2_conn_stat *cstat,
ngtcp2_cc_event_type event, ngtcp2_tstamp ts) {
(void)ccx;
(void)cstat;
(void)event;
(void)ts;
}
static void bbr_update_on_ack(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
bbr_update_model_and_state(cc, cstat, ack, ts);
bbr_update_control_parameters(cc, cstat, ack);
}
static void bbr_update_model_and_state(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack,
ngtcp2_tstamp ts) {
bbr_update_btl_bw(cc, cstat, ack);
bbr_check_cycle_phase(cc, cstat, ack, ts);
bbr_check_full_pipe(cc);
bbr_check_drain(cc, cstat, ts);
bbr_update_rtprop(cc, cstat, ts);
bbr_check_probe_rtt(cc, cstat, ts);
}
static void bbr_update_control_parameters(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
bbr_set_pacing_rate(cc, cstat);
bbr_set_send_quantum(cc, cstat);
bbr_set_cwnd(cc, cstat, ack);
}
static void bbr_on_transmit(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
bbr_handle_restart_from_idle(cc, cstat);
}
static void bbr_init_round_counting(ngtcp2_bbr_cc *cc) {
cc->next_round_delivered = 0;
cc->round_start = 0;
cc->round_count = 0;
}
static void bbr_update_round(ngtcp2_bbr_cc *cc, const ngtcp2_cc_ack *ack) {
if (ack->pkt_delivered >= cc->next_round_delivered) {
cc->next_round_delivered = cc->rst->delivered;
++cc->round_count;
cc->round_start = 1;
return;
}
cc->round_start = 0;
}
static void bbr_handle_recovery(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
if (cc->in_loss_recovery) {
if (ack->pkt_delivered >= cc->congestion_recovery_next_round_delivered) {
cc->packet_conservation = 0;
}
if (!in_congestion_recovery(cstat, ack->largest_acked_sent_ts)) {
cc->in_loss_recovery = 0;
cc->packet_conservation = 0;
bbr_restore_cwnd(cc, cstat);
}
return;
}
if (cc->congestion_recovery_start_ts != UINT64_MAX) {
cc->in_loss_recovery = 1;
bbr_save_cwnd(cc, cstat);
cstat->cwnd = cstat->bytes_in_flight +
ngtcp2_max(ack->bytes_delivered, cstat->max_udp_payload_size);
cstat->congestion_recovery_start_ts = cc->congestion_recovery_start_ts;
cc->congestion_recovery_start_ts = UINT64_MAX;
cc->packet_conservation = 1;
cc->congestion_recovery_next_round_delivered = cc->rst->delivered;
}
}
static void bbr_update_btl_bw(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
bbr_update_round(cc, ack);
bbr_handle_recovery(cc, cstat, ack);
if (cstat->delivery_rate_sec < cc->btl_bw && cc->rst->rs.is_app_limited) {
return;
}
ngtcp2_window_filter_update(&cc->btl_bw_filter, cstat->delivery_rate_sec,
cc->round_count);
cc->btl_bw = ngtcp2_window_filter_get_best(&cc->btl_bw_filter);
}
static void bbr_update_rtprop(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
cc->rtprop_expired = ts > cc->rtprop_stamp + NGTCP2_RTPROP_FILTERLEN;
/* Need valid RTT sample */
if (cstat->latest_rtt &&
(cstat->latest_rtt <= cc->rt_prop || cc->rtprop_expired)) {
cc->rt_prop = cstat->latest_rtt;
cc->rtprop_stamp = ts;
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV,
"bbr update RTprop=%" PRIu64, cc->rt_prop);
}
}
static void bbr_init_pacing_rate(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
double nominal_bandwidth =
(double)cc->initial_cwnd / (double)NGTCP2_MILLISECONDS;
cstat->pacing_rate = cc->pacing_gain * nominal_bandwidth;
}
static void bbr_set_pacing_rate_with_gain(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat,
double pacing_gain) {
double rate = pacing_gain * (double)cc->btl_bw / NGTCP2_SECONDS;
if (cc->filled_pipe || rate > cstat->pacing_rate) {
cstat->pacing_rate = rate;
}
}
static void bbr_set_pacing_rate(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
bbr_set_pacing_rate_with_gain(cc, cstat, cc->pacing_gain);
}
static void bbr_set_send_quantum(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
uint64_t send_quantum;
(void)cc;
if (cstat->pacing_rate < 1.2 * 1024 * 1024 / 8 / NGTCP2_SECONDS) {
cstat->send_quantum = cstat->max_udp_payload_size;
} else if (cstat->pacing_rate < 24.0 * 1024 * 1024 / 8 / NGTCP2_SECONDS) {
cstat->send_quantum = cstat->max_udp_payload_size * 2;
} else {
send_quantum =
(uint64_t)(cstat->pacing_rate * (double)(cstat->min_rtt == UINT64_MAX
? NGTCP2_MILLISECONDS
: cstat->min_rtt));
cstat->send_quantum = (size_t)ngtcp2_min(send_quantum, 64 * 1024);
}
cstat->send_quantum =
ngtcp2_max(cstat->send_quantum, cstat->max_udp_payload_size * 10);
}
static uint64_t bbr_inflight(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
double gain) {
uint64_t quanta = 3 * cstat->send_quantum;
double estimated_bdp;
if (cc->rt_prop == UINT64_MAX) {
/* no valid RTT samples yet */
return cc->initial_cwnd;
}
estimated_bdp = (double)cc->btl_bw * (double)cc->rt_prop / NGTCP2_SECONDS;
return (uint64_t)(gain * estimated_bdp) + quanta;
}
static void bbr_update_target_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
cc->target_cwnd = bbr_inflight(cc, cstat, cc->cwnd_gain);
}
static void bbr_modulate_cwnd_for_recovery(ngtcp2_bbr_cc *cc,
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_udp_payload_size);
} else {
cstat->cwnd = cstat->max_udp_payload_size;
}
}
if (cc->packet_conservation) {
cstat->cwnd =
ngtcp2_max(cstat->cwnd, cstat->bytes_in_flight + ack->bytes_delivered);
}
}
static void bbr_save_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
if (!cc->in_loss_recovery && cc->state != NGTCP2_BBR_STATE_PROBE_RTT) {
cc->prior_cwnd = cstat->cwnd;
return;
}
cc->prior_cwnd = ngtcp2_max(cc->prior_cwnd, cstat->cwnd);
}
static void bbr_restore_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat) {
cstat->cwnd = ngtcp2_max(cstat->cwnd, cc->prior_cwnd);
}
static uint64_t min_pipe_cwnd(size_t max_udp_payload_size) {
return max_udp_payload_size * 4;
}
static void bbr_modulate_cwnd_for_probe_rtt(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat) {
if (cc->state == NGTCP2_BBR_STATE_PROBE_RTT) {
cstat->cwnd =
ngtcp2_min(cstat->cwnd, min_pipe_cwnd(cstat->max_udp_payload_size));
}
}
static void bbr_set_cwnd(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack) {
bbr_update_target_cwnd(cc, cstat);
bbr_modulate_cwnd_for_recovery(cc, cstat, ack);
if (!cc->packet_conservation) {
if (cc->filled_pipe) {
cstat->cwnd =
ngtcp2_min(cstat->cwnd + ack->bytes_delivered, cc->target_cwnd);
} else if (cstat->cwnd < cc->target_cwnd ||
cc->rst->delivered < cc->initial_cwnd) {
cstat->cwnd += ack->bytes_delivered;
}
cstat->cwnd =
ngtcp2_max(cstat->cwnd, min_pipe_cwnd(cstat->max_udp_payload_size));
}
bbr_modulate_cwnd_for_probe_rtt(cc, cstat);
}
static void bbr_init(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp initial_ts) {
cc->pacing_gain = NGTCP2_BBR_HIGH_GAIN;
cc->prior_cwnd = 0;
cc->target_cwnd = 0;
cc->btl_bw = 0;
cc->rt_prop = UINT64_MAX;
cc->rtprop_stamp = initial_ts;
cc->cycle_stamp = UINT64_MAX;
cc->probe_rtt_done_stamp = UINT64_MAX;
cc->cycle_index = 0;
cc->rtprop_expired = 0;
cc->idle_restart = 0;
cc->packet_conservation = 0;
cc->probe_rtt_round_done = 0;
cc->congestion_recovery_start_ts = UINT64_MAX;
cc->congestion_recovery_next_round_delivered = 0;
cc->in_loss_recovery = 0;
cstat->send_quantum = cstat->max_udp_payload_size * 10;
ngtcp2_window_filter_init(&cc->btl_bw_filter, NGTCP2_BBR_BTL_BW_FILTERLEN);
bbr_init_round_counting(cc);
bbr_init_full_pipe(cc);
bbr_init_pacing_rate(cc, cstat);
bbr_enter_startup(cc);
}
static void bbr_enter_startup(ngtcp2_bbr_cc *cc) {
cc->state = NGTCP2_BBR_STATE_STARTUP;
cc->pacing_gain = NGTCP2_BBR_HIGH_GAIN;
cc->cwnd_gain = NGTCP2_BBR_HIGH_GAIN;
}
static void bbr_init_full_pipe(ngtcp2_bbr_cc *cc) {
cc->filled_pipe = 0;
cc->full_bw = 0;
cc->full_bw_count = 0;
}
static void bbr_check_full_pipe(ngtcp2_bbr_cc *cc) {
if (cc->filled_pipe || !cc->round_start || cc->rst->rs.is_app_limited) {
/* no need to check for a full pipe now. */
return;
}
/* cc->btl_bw still growing? */
if (cc->btl_bw * 100 >= cc->full_bw * 125) {
/* record new baseline level */
cc->full_bw = cc->btl_bw;
cc->full_bw_count = 0;
return;
}
/* another round w/o much growth */
++cc->full_bw_count;
if (cc->full_bw_count >= 3) {
cc->filled_pipe = 1;
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV,
"bbr filled pipe, btl_bw=%" PRIu64, cc->btl_bw);
}
}
static void bbr_enter_drain(ngtcp2_bbr_cc *cc) {
cc->state = NGTCP2_BBR_STATE_DRAIN;
/* pace slowly */
cc->pacing_gain = 1.0 / NGTCP2_BBR_HIGH_GAIN;
/* maintain cwnd */
cc->cwnd_gain = NGTCP2_BBR_HIGH_GAIN;
}
static void bbr_check_drain(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (cc->state == NGTCP2_BBR_STATE_STARTUP && cc->filled_pipe) {
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV,
"bbr exit Startup and enter Drain");
bbr_enter_drain(cc);
}
if (cc->state == NGTCP2_BBR_STATE_DRAIN &&
cstat->bytes_in_flight <= bbr_inflight(cc, cstat, 1.0)) {
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV,
"bbr exit Drain and enter ProbeBW");
/* we estimate queue is drained */
bbr_enter_probe_bw(cc, ts);
}
}
static void bbr_enter_probe_bw(ngtcp2_bbr_cc *cc, ngtcp2_tstamp ts) {
uint8_t rand;
cc->state = NGTCP2_BBR_STATE_PROBE_BW;
cc->pacing_gain = 1;
cc->cwnd_gain = 2;
assert(cc->rand);
cc->rand(&rand, 1, &cc->rand_ctx);
cc->cycle_index = NGTCP2_BBR_GAIN_CYCLELEN - 1 - (size_t)(rand * 7 / 256);
bbr_advance_cycle_phase(cc, ts);
}
static void bbr_check_cycle_phase(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
if (cc->state == NGTCP2_BBR_STATE_PROBE_BW &&
bbr_is_next_cycle_phase(cc, cstat, ack, ts)) {
bbr_advance_cycle_phase(cc, ts);
}
}
static void bbr_advance_cycle_phase(ngtcp2_bbr_cc *cc, ngtcp2_tstamp ts) {
cc->cycle_stamp = ts;
cc->cycle_index = (cc->cycle_index + 1) & (NGTCP2_BBR_GAIN_CYCLELEN - 1);
cc->pacing_gain = pacing_gain_cycle[cc->cycle_index];
}
static int bbr_is_next_cycle_phase(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
const ngtcp2_cc_ack *ack, ngtcp2_tstamp ts) {
int is_full_length = (ts - cc->cycle_stamp) > cc->rt_prop;
if (cc->pacing_gain > 1) {
return is_full_length && (ack->bytes_lost > 0 ||
ack->prior_bytes_in_flight >=
bbr_inflight(cc, cstat, cc->pacing_gain));
}
if (cc->pacing_gain < 1) {
return is_full_length ||
ack->prior_bytes_in_flight <= bbr_inflight(cc, cstat, 1);
}
return is_full_length;
}
static void bbr_handle_restart_from_idle(ngtcp2_bbr_cc *cc,
ngtcp2_conn_stat *cstat) {
if (cstat->bytes_in_flight == 0 && cc->rst->app_limited) {
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV, "bbr restart from idle");
cc->idle_restart = 1;
if (cc->state == NGTCP2_BBR_STATE_PROBE_BW) {
bbr_set_pacing_rate_with_gain(cc, cstat, 1);
}
}
}
static void bbr_check_probe_rtt(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
if (cc->state != NGTCP2_BBR_STATE_PROBE_RTT && cc->rtprop_expired &&
!cc->idle_restart) {
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV, "bbr enter ProbeRTT");
bbr_enter_probe_rtt(cc);
bbr_save_cwnd(cc, cstat);
cc->probe_rtt_done_stamp = UINT64_MAX;
}
if (cc->state == NGTCP2_BBR_STATE_PROBE_RTT) {
bbr_handle_probe_rtt(cc, cstat, ts);
}
cc->idle_restart = 0;
}
static void bbr_enter_probe_rtt(ngtcp2_bbr_cc *cc) {
cc->state = NGTCP2_BBR_STATE_PROBE_RTT;
cc->pacing_gain = 1;
cc->cwnd_gain = 1;
}
static void bbr_handle_probe_rtt(ngtcp2_bbr_cc *cc, ngtcp2_conn_stat *cstat,
ngtcp2_tstamp ts) {
uint64_t app_limited = cc->rst->delivered + cstat->bytes_in_flight;
/* Ignore low rate samples during NGTCP2_BBR_STATE_PROBE_RTT. */
cc->rst->app_limited = app_limited ? app_limited : 1;
if (cc->probe_rtt_done_stamp == UINT64_MAX &&
cstat->bytes_in_flight <= min_pipe_cwnd(cstat->max_udp_payload_size)) {
cc->probe_rtt_done_stamp = ts + NGTCP2_BBR_PROBE_RTT_DURATION;
cc->probe_rtt_round_done = 0;
cc->next_round_delivered = cc->rst->delivered;
return;
}
if (cc->probe_rtt_done_stamp != UINT64_MAX) {
if (cc->round_start) {
cc->probe_rtt_round_done = 1;
}
if (cc->probe_rtt_round_done && ts > cc->probe_rtt_done_stamp) {
cc->rtprop_stamp = ts;
bbr_restore_cwnd(cc, cstat);
bbr_exit_probe_rtt(cc, ts);
}
}
}
static void bbr_exit_probe_rtt(ngtcp2_bbr_cc *cc, ngtcp2_tstamp ts) {
if (cc->filled_pipe) {
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV,
"bbr exit ProbeRTT and enter ProbeBW");
bbr_enter_probe_bw(cc, ts);
return;
}
ngtcp2_log_info(cc->ccb.log, NGTCP2_LOG_EVENT_RCV,
"bbr exit ProbeRTT and enter Startup");
bbr_enter_startup(cc);
}
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