net/quic/congestion_control/pacing_sender.cc

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "net/quic/congestion_control/pacing_sender.h"
   6
   7 namespace net {
   8
   9 PacingSender::PacingSender(SendAlgorithmInterface* sender,
  10                            QuicTime::Delta alarm_granularity,
  11                            uint32 initial_packet_burst)
  12     : sender_(sender),
  13       alarm_granularity_(alarm_granularity),
  14       initial_packet_burst_(initial_packet_burst),
  15       burst_tokens_(initial_packet_burst),
  16       last_delayed_packet_sent_time_(QuicTime::Zero()),
  17       next_packet_send_time_(QuicTime::Zero()),
  18       was_last_send_delayed_(false),
  19       has_valid_rtt_(false) {
  20 }
  21
  22 PacingSender::~PacingSender() {}
  23
  24 void PacingSender::SetFromConfig(const QuicConfig& config, bool is_server) {
  25   // TODO(ianswett): Consider using the suggested RTT for pacing an initial
  26   // response.
  27   sender_->SetFromConfig(config, is_server);
  28 }
  29
  30 void PacingSender::OnIncomingQuicCongestionFeedbackFrame(
  31       const QuicCongestionFeedbackFrame& feedback,
  32       QuicTime feedback_receive_time) {
  33   sender_->OnIncomingQuicCongestionFeedbackFrame(
  34       feedback, feedback_receive_time);
  35 }
  36
  37 void PacingSender::OnCongestionEvent(bool rtt_updated,
  38                                      QuicByteCount bytes_in_flight,
  39                                      const CongestionMap& acked_packets,
  40                                      const CongestionMap& lost_packets) {
  41   if (rtt_updated) {
  42     has_valid_rtt_ = true;
  43   }
  44   sender_->OnCongestionEvent(
  45       rtt_updated, bytes_in_flight, acked_packets, lost_packets);
  46 }
  47
  48 bool PacingSender::OnPacketSent(
  49     QuicTime sent_time,
  50     QuicByteCount bytes_in_flight,
  51     QuicPacketSequenceNumber sequence_number,
  52     QuicByteCount bytes,
  53     HasRetransmittableData has_retransmittable_data) {
  54   // Only pace data packets once we have an updated RTT.
  55   const bool in_flight =
  56       sender_->OnPacketSent(sent_time, bytes_in_flight, sequence_number,
  57                             bytes, has_retransmittable_data);
  58   if (has_retransmittable_data != HAS_RETRANSMITTABLE_DATA || !has_valid_rtt_) {
  59     return in_flight;
  60   }
  61   if (burst_tokens_ > 0) {
  62     --burst_tokens_;
  63     was_last_send_delayed_ = false;
  64     last_delayed_packet_sent_time_ = QuicTime::Zero();
  65     next_packet_send_time_ = QuicTime::Zero();
  66     return in_flight;
  67   }
  68   // The next packet should be sent as soon as the current packets has
  69   // been transferred.  We pace at twice the rate of the underlying
  70   // sender's bandwidth estimate during slow start and 1.25x during congestion
  71   // avoidance to ensure pacing doesn't prevent us from filling the window.
  72   const float kPacingAggression = sender_->InSlowStart() ? 2 : 1.25;
  73   QuicTime::Delta delay =
  74       BandwidthEstimate().Scale(kPacingAggression).TransferTime(bytes);
  75   // If the last send was delayed, and the alarm took a long time to get
  76   // invoked, allow the connection to make up for lost time.
  77   if (was_last_send_delayed_) {
  78     next_packet_send_time_ = next_packet_send_time_.Add(delay);
  79     // The send was application limited if it takes longer than the
  80     // pacing delay between sent packets.
  81     const bool application_limited =
  82         last_delayed_packet_sent_time_.IsInitialized() &&
  83         sent_time > last_delayed_packet_sent_time_.Add(delay);
  84     const bool making_up_for_lost_time = next_packet_send_time_ <= sent_time;
  85     // As long as we're making up time and not application limited,
  86     // continue to consider the packets delayed, allowing the packets to be
  87     // sent immediately.
  88     if (making_up_for_lost_time && !application_limited) {
  89       last_delayed_packet_sent_time_ = sent_time;
  90     } else {
  91       was_last_send_delayed_ = false;
  92       last_delayed_packet_sent_time_ = QuicTime::Zero();
  93     }
  94   } else {
  95     next_packet_send_time_ =
  96         QuicTime::Max(next_packet_send_time_.Add(delay),
  97                       sent_time.Add(delay).Subtract(alarm_granularity_));
  98   }
  99   return in_flight;
 100 }
 101
 102 void PacingSender::OnRetransmissionTimeout(bool packets_retransmitted) {
 103   sender_->OnRetransmissionTimeout(packets_retransmitted);
 104 }
 105
 106 void PacingSender::RevertRetransmissionTimeout() {
 107   sender_->RevertRetransmissionTimeout();
 108 }
 109
 110 QuicTime::Delta PacingSender::TimeUntilSend(
 111       QuicTime now,
 112       QuicByteCount bytes_in_flight,
 113       HasRetransmittableData has_retransmittable_data) const {
 114   QuicTime::Delta time_until_send =
 115       sender_->TimeUntilSend(now, bytes_in_flight, has_retransmittable_data);
 116   if (!has_valid_rtt_) {
 117     // Don't pace if we don't have an updated RTT estimate.
 118     return time_until_send;
 119   }
 120   if (bytes_in_flight == 0) {
 121     // Add more burst tokens anytime the connection is entering quiescence.
 122     burst_tokens_ = initial_packet_burst_;
 123   }
 124   if (burst_tokens_ > 0) {
 125     // Don't pace if we have burst tokens available.
 126     return time_until_send;
 127   }
 128
 129   if (!time_until_send.IsZero()) {
 130     DCHECK(time_until_send.IsInfinite());
 131     // The underlying sender prevents sending.
 132     return time_until_send;
 133   }
 134
 135   if (has_retransmittable_data == NO_RETRANSMITTABLE_DATA) {
 136     // Don't pace ACK packets, since they do not count against CWND and do not
 137     // cause CWND to grow.
 138     return QuicTime::Delta::Zero();
 139   }
 140
 141   // If the next send time is within the alarm granularity, send immediately.
 142   if (next_packet_send_time_ > now.Add(alarm_granularity_)) {
 143     DVLOG(1) << "Delaying packet: "
 144              << next_packet_send_time_.Subtract(now).ToMicroseconds();
 145     was_last_send_delayed_ = true;
 146     return next_packet_send_time_.Subtract(now);
 147   }
 148
 149   DVLOG(1) << "Sending packet now";
 150   return QuicTime::Delta::Zero();
 151 }
 152
 153 QuicBandwidth PacingSender::BandwidthEstimate() const {
 154   return sender_->BandwidthEstimate();
 155 }
 156
 157 bool PacingSender::HasReliableBandwidthEstimate() const {
 158   return sender_->HasReliableBandwidthEstimate();
 159 }
 160
 161 QuicTime::Delta PacingSender::RetransmissionDelay() const {
 162   return sender_->RetransmissionDelay();
 163 }
 164
 165 QuicByteCount PacingSender::GetCongestionWindow() const {
 166   return sender_->GetCongestionWindow();
 167 }
 168
 169 bool PacingSender::InSlowStart() const {
 170   return sender_->InSlowStart();
 171 }
 172
 173 bool PacingSender::InRecovery() const {
 174   return sender_->InRecovery();
 175 }
 176
 177 QuicByteCount PacingSender::GetSlowStartThreshold() const {
 178   return sender_->GetSlowStartThreshold();
 179 }
 180
 181 CongestionControlType PacingSender::GetCongestionControlType() const {
 182   return sender_->GetCongestionControlType();
 183 }
 184
 185 }  // namespace net