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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "quic/core/congestion_control/bbr2_startup.h"
#include "quic/core/congestion_control/bbr2_misc.h"
#include "quic/core/congestion_control/bbr2_sender.h"
#include "quic/core/quic_bandwidth.h"
#include "quic/core/quic_types.h"
#include "quic/platform/api/quic_flags.h"
#include "quic/platform/api/quic_logging.h"
namespace quic {
Bbr2StartupMode::Bbr2StartupMode(const Bbr2Sender* sender,
Bbr2NetworkModel* model,
QuicTime now)
: Bbr2ModeBase(sender, model) {
// Clear some startup stats if |sender_->connection_stats_| has been used by
// another sender, which happens e.g. when QuicConnection switch send
// algorithms.
sender_->connection_stats_->slowstart_count = 1;
sender_->connection_stats_->slowstart_duration = QuicTimeAccumulator();
sender_->connection_stats_->slowstart_duration.Start(now);
if (sender->Params().bw_startup) {
// Enter() is never called for Startup, so the gains needs to be set here.
model_->set_pacing_gain(Params().startup_pacing_gain);
model_->set_cwnd_gain(Params().startup_cwnd_gain);
}
}
void Bbr2StartupMode::Enter(QuicTime /*now*/,
const Bbr2CongestionEvent* /*congestion_event*/) {
QUIC_BUG << "Bbr2StartupMode::Enter should not be called";
}
void Bbr2StartupMode::Leave(QuicTime now,
const Bbr2CongestionEvent* /*congestion_event*/) {
sender_->connection_stats_->slowstart_duration.Stop(now);
// Clear bandwidth_lo if it's set during STARTUP.
model_->clear_bandwidth_lo();
}
Bbr2Mode Bbr2StartupMode::OnCongestionEvent(
QuicByteCount /*prior_in_flight*/,
QuicTime /*event_time*/,
const AckedPacketVector& /*acked_packets*/,
const LostPacketVector& /*lost_packets*/,
const Bbr2CongestionEvent& congestion_event) {
if (!model_->full_bandwidth_reached() && congestion_event.end_of_round_trip) {
// TCP BBR always exits upon excessive losses. QUIC BBRv1 does not exits
// upon excessive losses, if enough bandwidth growth is observed.
Bbr2NetworkModel::BandwidthGrowth bw_growth =
model_->CheckBandwidthGrowth(congestion_event);
if (Params().always_exit_startup_on_excess_loss ||
(bw_growth == Bbr2NetworkModel::NO_GROWTH ||
bw_growth == Bbr2NetworkModel::EXIT)) {
CheckExcessiveLosses(congestion_event);
}
}
if (Params().decrease_startup_pacing_at_end_of_round) {
QUICHE_DCHECK_GT(model_->pacing_gain(), 0);
QUICHE_DCHECK(Params().bw_startup);
if (congestion_event.end_of_round_trip &&
!congestion_event.last_sample_is_app_limited) {
// Multiply by startup_pacing_gain, so if the bandwidth doubles,
// the pacing gain will be the full startup_pacing_gain.
if (max_bw_at_round_beginning_ > QuicBandwidth::Zero()) {
const float bandwidth_ratio =
std::max(1., model_->MaxBandwidth().ToBitsPerSecond() /
static_cast<double>(
max_bw_at_round_beginning_.ToBitsPerSecond()));
// Even when bandwidth isn't increasing, use a gain large enough to
// cause a startup_full_bw_threshold increase.
const float new_gain =
((bandwidth_ratio - 1) * (Params().startup_pacing_gain -
Params().startup_full_bw_threshold)) +
Params().startup_full_bw_threshold;
// Allow the pacing gain to decrease.
model_->set_pacing_gain(
std::min(Params().startup_pacing_gain, new_gain));
// Clear bandwidth_lo if it's less than the pacing rate.
// This avoids a constantly app-limited flow from having it's pacing
// gain effectively decreased below 1.25.
if (model_->bandwidth_lo() <
model_->MaxBandwidth() * model_->pacing_gain()) {
model_->clear_bandwidth_lo();
}
}
max_bw_at_round_beginning_ = model_->MaxBandwidth();
}
} else if (!Params().bw_startup) {
// When the flag is enabled, set these in the constructor.
model_->set_pacing_gain(Params().startup_pacing_gain);
model_->set_cwnd_gain(Params().startup_cwnd_gain);
}
// TODO(wub): Maybe implement STARTUP => PROBE_RTT.
return model_->full_bandwidth_reached() ? Bbr2Mode::DRAIN : Bbr2Mode::STARTUP;
}
void Bbr2StartupMode::CheckExcessiveLosses(
const Bbr2CongestionEvent& congestion_event) {
QUICHE_DCHECK(congestion_event.end_of_round_trip);
if (model_->full_bandwidth_reached()) {
return;
}
// At the end of a round trip. Check if loss is too high in this round.
if (model_->IsInflightTooHigh(congestion_event,
Params().startup_full_loss_count)) {
QuicByteCount new_inflight_hi = model_->BDP();
if (Params().startup_loss_exit_use_max_delivered_for_inflight_hi) {
if (new_inflight_hi < model_->max_bytes_delivered_in_round()) {
new_inflight_hi = model_->max_bytes_delivered_in_round();
}
}
QUIC_DVLOG(3) << sender_ << " Exiting STARTUP due to loss. inflight_hi:"
<< new_inflight_hi;
// TODO(ianswett): Add a shared method to set inflight_hi in the model.
model_->set_inflight_hi(new_inflight_hi);
model_->set_full_bandwidth_reached();
sender_->connection_stats_->bbr_exit_startup_due_to_loss = true;
}
}
Bbr2StartupMode::DebugState Bbr2StartupMode::ExportDebugState() const {
DebugState s;
s.full_bandwidth_reached = model_->full_bandwidth_reached();
s.full_bandwidth_baseline = model_->full_bandwidth_baseline();
s.round_trips_without_bandwidth_growth =
model_->rounds_without_bandwidth_growth();
return s;
}
std::ostream& operator<<(std::ostream& os,
const Bbr2StartupMode::DebugState& state) {
os << "[STARTUP] full_bandwidth_reached: " << state.full_bandwidth_reached
<< "\n";
os << "[STARTUP] full_bandwidth_baseline: " << state.full_bandwidth_baseline
<< "\n";
os << "[STARTUP] round_trips_without_bandwidth_growth: "
<< state.round_trips_without_bandwidth_growth << "\n";
return os;
}
const Bbr2Params& Bbr2StartupMode::Params() const {
return sender_->Params();
}
} // namespace quic