Land Recent QUIC Changes.

net/quic/congestion_control/pacing_sender.cc

 // Copyright (c) 2013 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/pacing_sender.h"
 
 namespace net {
 
 PacingSender::PacingSender(SendAlgorithmInterface* sender,
                            QuicTime::Delta alarm_granularity)
     : sender_(sender),
       alarm_granularity_(alarm_granularity),
+      last_delayed_packet_sent_time_(QuicTime::Zero()),
       next_packet_send_time_(QuicTime::Zero()),
       was_last_send_delayed_(false),
       has_valid_rtt_(false) {
 }
 
 PacingSender::~PacingSender() {}
 
 void PacingSender::SetFromConfig(const QuicConfig& config, bool is_server) {
   sender_->SetFromConfig(config, is_server);
 }
@@ skipping 24 matching lines @@
     HasRetransmittableData has_retransmittable_data) {
   // Only pace data packets once we have an updated RTT.
   if (has_retransmittable_data == HAS_RETRANSMITTABLE_DATA && has_valid_rtt_) {
     // The next packet should be sent as soon as the current packets has
     // been transferred.  We pace at twice the rate of the underlying
     // sender's bandwidth estimate to help ensure that pacing doesn't become
     // a bottleneck.
     const float kPacingAggression = 2;
     QuicTime::Delta delay =
         BandwidthEstimate().Scale(kPacingAggression).TransferTime(bytes);
-    next_packet_send_time_ = next_packet_send_time_.Add(delay);
+    // If the last send was delayed, and the alarm took a long time to get
+    // invoked, allow the connection to make up for lost time.
+    if (was_last_send_delayed_) {
+      next_packet_send_time_ = next_packet_send_time_.Add(delay);
+      // As long as we're making up time and not application limited,
+      // continue to consider the packets delayed.
+      // The send was application limited if it takes longer than the
+      // pacing delay between sent packets.
+      const bool application_limited =
+          last_delayed_packet_sent_time_.IsInitialized() &&
+          sent_time > last_delayed_packet_sent_time_.Add(delay);
+      const bool making_up_for_lost_time = next_packet_send_time_ > sent_time;
+      if (making_up_for_lost_time || application_limited) {
+        was_last_send_delayed_ = false;
+        last_delayed_packet_sent_time_ = QuicTime::Zero();
+      } else {
+        last_delayed_packet_sent_time_ = sent_time;
+      }
+    } else {
+      next_packet_send_time_ =
+          QuicTime::Max(next_packet_send_time_.Add(delay),
+                        sent_time.Add(delay).Subtract(alarm_granularity_));
+    }
   }
   return sender_->OnPacketSent(sent_time, bytes_in_flight, sequence_number,
                                bytes, has_retransmittable_data);
 }
 
 void PacingSender::OnRetransmissionTimeout(bool packets_retransmitted) {
   sender_->OnRetransmissionTimeout(packets_retransmitted);
 }
 
 QuicTime::Delta PacingSender::TimeUntilSend(
@@ skipping 12 matching lines @@
     // The underlying sender prevents sending.
     return time_until_send;
   }
 
   if (has_retransmittable_data == NO_RETRANSMITTABLE_DATA) {
     // Don't pace ACK packets, since they do not count against CWND and do not
     // cause CWND to grow.
     return QuicTime::Delta::Zero();
   }
 
-  if (!was_last_send_delayed_ &&
-      (!next_packet_send_time_.IsInitialized() ||
-       now > next_packet_send_time_.Add(alarm_granularity_))) {
-    // An alarm did not go off late, instead the application is "slow"
-    // delivering data.  In this case, we restrict the amount of lost time
-    // that we can make up for.
-    next_packet_send_time_ = now.Subtract(alarm_granularity_);
-  }
-
-  // If the end of the epoch is far enough in the future, delay the send.
+  // If the next send time is within the alarm granularity, send immediately.
   if (next_packet_send_time_ > now.Add(alarm_granularity_)) {
-    was_last_send_delayed_ = true;
     DVLOG(1) << "Delaying packet: "
              << next_packet_send_time_.Subtract(now).ToMicroseconds();
+    was_last_send_delayed_ = true;
     return next_packet_send_time_.Subtract(now);
   }
 
-  // Sent it immediately.  The epoch end will be adjusted in OnPacketSent.
-  was_last_send_delayed_ = false;
   DVLOG(1) << "Sending packet now";
   return QuicTime::Delta::Zero();
 }
 
 QuicBandwidth PacingSender::BandwidthEstimate() const {
   return sender_->BandwidthEstimate();
 }
 
 QuicTime::Delta PacingSender::RetransmissionDelay() const {
   return sender_->RetransmissionDelay();
 }
 
 QuicByteCount PacingSender::GetCongestionWindow() const {
   return sender_->GetCongestionWindow();
 }
 
 }  // namespace net