Deprecate FLAG_quic_use_new_tcp_sender

net/quic/congestion_control/tcp_cubic_bytes_sender.cc

-// Copyright (c) 2015 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 "net/quic/congestion_control/tcp_cubic_bytes_sender.h"
-
-#include <algorithm>
-
-#include "net/quic/congestion_control/prr_sender.h"
-#include "net/quic/congestion_control/rtt_stats.h"
-#include "net/quic/crypto/crypto_protocol.h"
-#include "net/quic/proto/cached_network_parameters.pb.h"
-#include "net/quic/quic_bug_tracker.h"
-#include "net/quic/quic_flags.h"
-
-using std::max;
-using std::min;
-
-namespace net {
-
-namespace {
-// Constants based on TCP defaults.
-// The minimum cwnd based on RFC 3782 (TCP NewReno) for cwnd reductions on a
-// fast retransmission.
-const QuicByteCount kDefaultMinimumCongestionWindow = 2 * kDefaultTCPMSS;
-const QuicByteCount kMaxBurstBytes = 3 * kDefaultTCPMSS;
-const float kRenoBeta = 0.7f;             // Reno backoff factor.
-const uint32_t kDefaultNumConnections = 2;  // N-connection emulation.
-}  // namespace
-
-TcpCubicBytesSender::TcpCubicBytesSender(
-    const QuicClock* clock,
-    const RttStats* rtt_stats,
-    bool reno,
-    QuicPacketCount initial_tcp_congestion_window,
-    QuicPacketCount max_congestion_window,
-    QuicConnectionStats* stats)
-    : cubic_(clock),
-      rtt_stats_(rtt_stats),
-      stats_(stats),
-      reno_(reno),
-      num_connections_(kDefaultNumConnections),
-      num_acked_packets_(0),
-      largest_sent_packet_number_(0),
-      largest_acked_packet_number_(0),
-      largest_sent_at_last_cutback_(0),
-      congestion_window_(initial_tcp_congestion_window * kDefaultTCPMSS),
-      min_congestion_window_(kDefaultMinimumCongestionWindow),
-      min4_mode_(false),
-      max_congestion_window_(max_congestion_window * kDefaultTCPMSS),
-      slowstart_threshold_(max_congestion_window * kDefaultTCPMSS),
-      last_cutback_exited_slowstart_(false),
-      initial_tcp_congestion_window_(initial_tcp_congestion_window *
-                                     kDefaultTCPMSS),
-      initial_max_tcp_congestion_window_(max_congestion_window *
-                                         kDefaultTCPMSS),
-      slow_start_large_reduction_(false) {}
-
-TcpCubicBytesSender::~TcpCubicBytesSender() {}
-
-void TcpCubicBytesSender::SetFromConfig(const QuicConfig& config,
-                                        Perspective perspective) {
-  if (perspective == Perspective::IS_SERVER) {
-    if (config.HasReceivedConnectionOptions() &&
-        ContainsQuicTag(config.ReceivedConnectionOptions(), kIW10)) {
-      // Initial window experiment.
-      congestion_window_ = 10 * kDefaultTCPMSS;
-    }
-    if (config.HasReceivedConnectionOptions() &&
-        ContainsQuicTag(config.ReceivedConnectionOptions(), kMIN1)) {
-      // Min CWND experiment.
-      min_congestion_window_ = kDefaultTCPMSS;
-    }
-    if (config.HasReceivedConnectionOptions() &&
-        ContainsQuicTag(config.ReceivedConnectionOptions(), kMIN4)) {
-      // Min CWND of 4 experiment.
-      min4_mode_ = true;
-      min_congestion_window_ = kDefaultTCPMSS;
-    }
-    if (config.HasReceivedConnectionOptions() &&
-        ContainsQuicTag(config.ReceivedConnectionOptions(), kSSLR)) {
-      // Slow Start Fast Exit experiment.
-      slow_start_large_reduction_ = true;
-    }
-  }
-}
-
-void TcpCubicBytesSender::ResumeConnectionState(
-    const CachedNetworkParameters& cached_network_params,
-    bool max_bandwidth_resumption) {
-  QuicBandwidth bandwidth = QuicBandwidth::FromBytesPerSecond(
-      max_bandwidth_resumption
-          ? cached_network_params.max_bandwidth_estimate_bytes_per_second()
-          : cached_network_params.bandwidth_estimate_bytes_per_second());
-  QuicTime::Delta rtt_ms =
-      QuicTime::Delta::FromMilliseconds(cached_network_params.min_rtt_ms());
-
-  // Make sure CWND is in appropriate range (in case of bad data).
-  QuicByteCount new_congestion_window = bandwidth.ToBytesPerPeriod(rtt_ms);
-  congestion_window_ =
-      max(min(new_congestion_window, kMaxCongestionWindow * kDefaultTCPMSS),
-          kMinCongestionWindowForBandwidthResumption * kDefaultTCPMSS);
-}
-
-void TcpCubicBytesSender::SetNumEmulatedConnections(int num_connections) {
-  num_connections_ = max(1, num_connections);
-  cubic_.SetNumConnections(num_connections_);
-}
-
-void TcpCubicBytesSender::SetMaxCongestionWindow(
-    QuicByteCount max_congestion_window) {
-  max_congestion_window_ = max_congestion_window;
-}
-
-float TcpCubicBytesSender::RenoBeta() const {
-  // kNConnectionBeta is the backoff factor after loss for our N-connection
-  // emulation, which emulates the effective backoff of an ensemble of N
-  // TCP-Reno connections on a single loss event. The effective multiplier is
-  // computed as:
-  return (num_connections_ - 1 + kRenoBeta) / num_connections_;
-}
-
-void TcpCubicBytesSender::OnCongestionEvent(
-    bool rtt_updated,
-    QuicByteCount bytes_in_flight,
-    const CongestionVector& acked_packets,
-    const CongestionVector& lost_packets) {
-  if (rtt_updated && InSlowStart() &&
-      hybrid_slow_start_.ShouldExitSlowStart(
-          rtt_stats_->latest_rtt(), rtt_stats_->min_rtt(),
-          congestion_window_ / kDefaultTCPMSS)) {
-    slowstart_threshold_ = congestion_window_;
-  }
-  for (CongestionVector::const_iterator it = lost_packets.begin();
-       it != lost_packets.end(); ++it) {
-    OnPacketLost(it->first, bytes_in_flight);
-  }
-  for (CongestionVector::const_iterator it = acked_packets.begin();
-       it != acked_packets.end(); ++it) {
-    OnPacketAcked(it->first, it->second, bytes_in_flight);
-  }
-}
-
-void TcpCubicBytesSender::OnPacketAcked(QuicPacketNumber acked_packet_number,
-                                        QuicByteCount acked_bytes,
-                                        QuicByteCount bytes_in_flight) {
-  largest_acked_packet_number_ =
-      max(acked_packet_number, largest_acked_packet_number_);
-  if (InRecovery()) {
-    // PRR is used when in recovery.
-    prr_.OnPacketAcked(acked_bytes);
-    return;
-  }
-  MaybeIncreaseCwnd(acked_packet_number, acked_bytes, bytes_in_flight);
-  if (InSlowStart()) {
-    hybrid_slow_start_.OnPacketAcked(acked_packet_number);
-  }
-}
-
-void TcpCubicBytesSender::OnPacketLost(QuicPacketNumber packet_number,
-                                       QuicByteCount bytes_in_flight) {
-  // TCP NewReno (RFC6582) says that once a loss occurs, any losses in packets
-  // already sent should be treated as a single loss event, since it's expected.
-  if (packet_number <= largest_sent_at_last_cutback_) {
-    if (last_cutback_exited_slowstart_) {
-      ++stats_->slowstart_packets_lost;
-      if (slow_start_large_reduction_) {
-        // Reduce congestion window by 1 MSS for every loss.
-        congestion_window_ =
-            max(congestion_window_ - kDefaultTCPMSS, min_congestion_window_);
-        slowstart_threshold_ = congestion_window_;
-      }
-    }
-    DVLOG(1) << "Ignoring loss for largest_missing:" << packet_number
-             << " because it was sent prior to the last CWND cutback.";
-    return;
-  }
-  ++stats_->tcp_loss_events;
-  last_cutback_exited_slowstart_ = InSlowStart();
-  if (InSlowStart()) {
-    ++stats_->slowstart_packets_lost;
-  }
-
-  prr_.OnPacketLost(bytes_in_flight);
-
-  // TODO(jri): Separate out all of slow start into a separate class.
-  if (slow_start_large_reduction_ && InSlowStart()) {
-    DCHECK_LT(kDefaultTCPMSS, congestion_window_);
-    congestion_window_ = congestion_window_ - kDefaultTCPMSS;
-  } else if (reno_) {
-    congestion_window_ = congestion_window_ * RenoBeta();
-  } else {
-    congestion_window_ =
-        cubic_.CongestionWindowAfterPacketLoss(congestion_window_);
-  }
-  // Enforce TCP's minimum congestion window of 2*MSS.
-  if (congestion_window_ < min_congestion_window_) {
-    congestion_window_ = min_congestion_window_;
-  }
-  slowstart_threshold_ = congestion_window_;
-  largest_sent_at_last_cutback_ = largest_sent_packet_number_;
-  // Reset packet count from congestion avoidance mode. We start counting again
-  // when we're out of recovery.
-  num_acked_packets_ = 0;
-  DVLOG(1) << "Incoming loss; congestion window: " << congestion_window_
-           << " slowstart threshold: " << slowstart_threshold_;
-}
-
-bool TcpCubicBytesSender::OnPacketSent(
-    QuicTime /*sent_time*/,
-    QuicByteCount /*bytes_in_flight*/,
-    QuicPacketNumber packet_number,
-    QuicByteCount bytes,
-    HasRetransmittableData is_retransmittable) {
-  if (InSlowStart()) {
-    ++(stats_->slowstart_packets_sent);
-  }
-
-  // Only update bytes_in_flight_ for data packets.
-  if (is_retransmittable != HAS_RETRANSMITTABLE_DATA) {
-    return false;
-  }
-  if (InRecovery()) {
-    // PRR is used when in recovery.
-    prr_.OnPacketSent(bytes);
-  }
-  DCHECK_LT(largest_sent_packet_number_, packet_number);
-  largest_sent_packet_number_ = packet_number;
-  hybrid_slow_start_.OnPacketSent(packet_number);
-  return true;
-}
-
-QuicTime::Delta TcpCubicBytesSender::TimeUntilSend(
-    QuicTime /* now */,
-    QuicByteCount bytes_in_flight,
-    HasRetransmittableData has_retransmittable_data) const {
-  if (has_retransmittable_data == NO_RETRANSMITTABLE_DATA) {
-    DCHECK(!FLAGS_quic_respect_send_alarm2);
-    // For TCP we can always send an ACK immediately.
-    return QuicTime::Delta::Zero();
-  }
-  if (InRecovery()) {
-    // PRR is used when in recovery.
-    return prr_.TimeUntilSend(GetCongestionWindow(), bytes_in_flight,
-                              slowstart_threshold_);
-  }
-  if (GetCongestionWindow() > bytes_in_flight) {
-    return QuicTime::Delta::Zero();
-  }
-  if (min4_mode_ && bytes_in_flight < 4 * kDefaultTCPMSS) {
-    return QuicTime::Delta::Zero();
-  }
-  return QuicTime::Delta::Infinite();
-}
-
-QuicBandwidth TcpCubicBytesSender::PacingRate() const {
-  // We pace at twice the rate of the underlying sender's bandwidth estimate
-  // during slow start and 1.25x during congestion avoidance to ensure pacing
-  // doesn't prevent us from filling the window.
-  QuicTime::Delta srtt = rtt_stats_->smoothed_rtt();
-  if (srtt.IsZero()) {
-    srtt = QuicTime::Delta::FromMicroseconds(rtt_stats_->initial_rtt_us());
-  }
-  const QuicBandwidth bandwidth =
-      QuicBandwidth::FromBytesAndTimeDelta(GetCongestionWindow(), srtt);
-  return bandwidth.Scale(InSlowStart() ? 2 : 1.25);
-}
-
-QuicBandwidth TcpCubicBytesSender::BandwidthEstimate() const {
-  QuicTime::Delta srtt = rtt_stats_->smoothed_rtt();
-  if (srtt.IsZero()) {
-    // If we haven't measured an rtt, the bandwidth estimate is unknown.
-    return QuicBandwidth::Zero();
-  }
-  return QuicBandwidth::FromBytesAndTimeDelta(GetCongestionWindow(), srtt);
-}
-
-QuicTime::Delta TcpCubicBytesSender::RetransmissionDelay() const {
-  if (rtt_stats_->smoothed_rtt().IsZero()) {
-    return QuicTime::Delta::Zero();
-  }
-  return rtt_stats_->smoothed_rtt().Add(
-      rtt_stats_->mean_deviation().Multiply(4));
-}
-
-QuicByteCount TcpCubicBytesSender::GetCongestionWindow() const {
-  return congestion_window_;
-}
-
-bool TcpCubicBytesSender::InSlowStart() const {
-  return congestion_window_ < slowstart_threshold_;
-}
-
-QuicByteCount TcpCubicBytesSender::GetSlowStartThreshold() const {
-  return slowstart_threshold_;
-}
-
-bool TcpCubicBytesSender::IsCwndLimited(QuicByteCount bytes_in_flight) const {
-  if (bytes_in_flight >= congestion_window_) {
-    return true;
-  }
-  const QuicByteCount available_bytes = congestion_window_ - bytes_in_flight;
-  const bool slow_start_limited =
-      InSlowStart() && bytes_in_flight > congestion_window_ / 2;
-  return slow_start_limited || available_bytes <= kMaxBurstBytes;
-}
-
-bool TcpCubicBytesSender::InRecovery() const {
-  return largest_acked_packet_number_ <= largest_sent_at_last_cutback_ &&
-         largest_acked_packet_number_ != 0;
-}
-
-// Called when we receive an ack. Normal TCP tracks how many packets one ack
-// represents, but quic has a separate ack for each packet.
-void TcpCubicBytesSender::MaybeIncreaseCwnd(
-    QuicPacketNumber acked_packet_number,
-    QuicByteCount acked_bytes,
-    QuicByteCount bytes_in_flight) {
-  QUIC_BUG_IF(InRecovery()) << "Never increase the CWND during recovery.";
-  // Do not increase the congestion window unless the sender is close to using
-  // the current window.
-  if (!IsCwndLimited(bytes_in_flight)) {
-    cubic_.OnApplicationLimited();
-    return;
-  }
-  if (congestion_window_ >= max_congestion_window_) {
-    return;
-  }
-  if (InSlowStart()) {
-    // TCP slow start, exponential growth, increase by one for each ACK.
-    congestion_window_ += kDefaultTCPMSS;
-    DVLOG(1) << "Slow start; congestion window: " << congestion_window_
-             << " slowstart threshold: " << slowstart_threshold_;
-    return;
-  }
-  // Congestion avoidance.
-  if (reno_) {
-    // Classic Reno congestion avoidance.
-    ++num_acked_packets_;
-    // Divide by num_connections to smoothly increase the CWND at a faster rate
-    // than conventional Reno.
-    if (num_acked_packets_ * num_connections_ >=
-        congestion_window_ / kDefaultTCPMSS) {
-      congestion_window_ += kDefaultTCPMSS;
-      num_acked_packets_ = 0;
-    }
-
-    DVLOG(1) << "Reno; congestion window: " << congestion_window_
-             << " slowstart threshold: " << slowstart_threshold_
-             << " congestion window count: " << num_acked_packets_;
-  } else {
-    congestion_window_ =
-        min(max_congestion_window_,
-            cubic_.CongestionWindowAfterAck(acked_bytes, congestion_window_,
-                                            rtt_stats_->min_rtt()));
-    DVLOG(1) << "Cubic; congestion window: " << congestion_window_
-             << " slowstart threshold: " << slowstart_threshold_;
-  }
-}
-
-void TcpCubicBytesSender::OnRetransmissionTimeout(bool packets_retransmitted) {
-  largest_sent_at_last_cutback_ = 0;
-  if (!packets_retransmitted) {
-    return;
-  }
-  cubic_.Reset();
-  hybrid_slow_start_.Restart();
-  slowstart_threshold_ = congestion_window_ / 2;
-  congestion_window_ = min_congestion_window_;
-}
-
-CongestionControlType TcpCubicBytesSender::GetCongestionControlType() const {
-  return reno_ ? kRenoBytes : kCubicBytes;
-}
-
-void TcpCubicBytesSender::OnConnectionMigration() {
-  hybrid_slow_start_.Restart();
-  cubic_.Reset();
-  prr_ = PrrSender();
-  num_acked_packets_ = 0;
-  largest_sent_packet_number_ = 0;
-  largest_acked_packet_number_ = 0;
-  largest_sent_at_last_cutback_ = 0;
-  congestion_window_ = initial_tcp_congestion_window_;
-  max_congestion_window_ = initial_max_tcp_congestion_window_;
-  slowstart_threshold_ = initial_max_tcp_congestion_window_;
-  last_cutback_exited_slowstart_ = false;
-}
-
-}  // namespace net