Reset QUIC's retransmission counters whenever a new packet is acked

net/quic/quic_sent_packet_manager.cc

 // Copyright 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/quic_sent_packet_manager.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "net/quic/congestion_control/pacing_sender.h"
 #include "net/quic/quic_ack_notifier_manager.h"
@@ skipping 163 matching lines @@
   }
   previous_transmissions->insert(new_sequence_number);
   unacked_packets_[new_sequence_number].previous_transmissions =
       previous_transmissions;
 
   DCHECK(HasRetransmittableFrames(new_sequence_number));
 }
 
 bool QuicSentPacketManager::OnIncomingAck(
     const ReceivedPacketInfo& received_info, QuicTime ack_receive_time) {
-  // Determine if the least unacked sequence number is being acked.
-  QuicPacketSequenceNumber least_unacked_sent_before =
-      GetLeastUnackedSentPacket();
-  // TODO(ianswett): Consider a non-TCP metric for determining the connection
-  // is making progress, since QUIC has out of order delivery.
-  bool new_least_unacked = !IsAwaitingPacket(received_info,
-                                             least_unacked_sent_before);
-
+  // We rely on delta_time_largest_observed to compute an RTT estimate, so
+  // we only update rtt when the largest observed gets acked.
+  bool largest_observed_acked =
+      ContainsKey(unacked_packets_, received_info.largest_observed);
   MaybeUpdateRTT(received_info, ack_receive_time);
   HandleAckForSentPackets(received_info);
   MaybeRetransmitOnAckFrame(received_info, ack_receive_time);
 
-  if (new_least_unacked) {
+  // Anytime we are making forward progress and have a new RTT estimate, reset
+  // the backoff counters.
+  if (largest_observed_acked) {
     // Reset all retransmit counters any time a new packet is acked.
     consecutive_rto_count_ = 0;
     consecutive_tlp_count_ = 0;
     consecutive_crypto_retransmission_count_ = 0;
   }
 
   // Always reset the retransmission alarm when an ack comes in, since we now
   // have a better estimate of the current rtt than when it was set.
   return true;
 }
@@ skipping 790 matching lines @@
   }
   previous_transmissions->erase(sequence_number);
   if (previous_transmissions->size() == 1) {
     QuicPacketSequenceNumber current = *previous_transmissions->begin();
     unacked_packets_[current].previous_transmissions = NULL;
     delete previous_transmissions;
   }
 }
 
 }  // namespace net