Throttle Socket watcher RTT notifications from QUIC

net/quic/chromium/quic_connection_logger.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/chromium/quic_connection_logger.h"
 
 #include <algorithm>
 #include <limits>
 #include <memory>
 #include <utility>
@@ skipping 668 matching lines @@
   float num_received = largest_received_packet_number_ - num_packets_received_;
   return num_received / largest_received_packet_number_;
 }
 
 void QuicConnectionLogger::OnRttChanged(QuicTime::Delta rtt) const {
   // Notify socket performance watcher of the updated RTT value.
   if (!socket_performance_watcher_)
     return;
 
   int64_t microseconds = rtt.ToMicroseconds();
-  if (microseconds != 0) {
+  if (microseconds != 0 &&
+      socket_performance_watcher_->ShouldNotifyUpdatedRTT()) {
     socket_performance_watcher_->OnUpdatedRTTAvailable(

[Ryan Hamilton, 2017/02/15 23:08:16]

I guess this is fine, but any reason not to make the impl of
OnUpdatedRTTAvailable do:

OnUpdatedRTTAvailable() {
 if (!ShouldNotifyUpdatedRTT())
   return;
  ...
}

And leave callers unchanged?

[tbansal1, 2017/02/15 23:16:12]

The reason is that we do not want TCP Socket Posix to make a syscall unless the
Socket Watcher is interested in receiving a reading. So, the socket first checks
if the Watcher is interested in the reading before making any effort to generate
one.

         base::TimeDelta::FromMicroseconds(rtt.ToMicroseconds()));
   }
 }
 
 void QuicConnectionLogger::RecordAggregatePacketLossRate() const {
   // For short connections under 22 packets in length, we'll rely on the
   // Net.QuicSession.21CumulativePacketsReceived_* histogram to indicate packet
   // loss rates.  This way we avoid tremendously anomalous contributions to our
   // histogram.  (e.g., if we only got 5 packets, but lost 1, we'd otherwise
   // record a 20% loss in this histogram!). We may still get some strange data
   // (1 loss in 22 is still high :-/).
   if (largest_received_packet_number_ <= 21)
     return;
 
   string prefix("Net.QuicSession.PacketLossRate_");
   base::HistogramBase* histogram = base::Histogram::FactoryGet(
       prefix + connection_description_, 1, 1000, 75,
       base::HistogramBase::kUmaTargetedHistogramFlag);
   histogram->Add(static_cast<base::HistogramBase::Sample>(
       ReceivedPacketLossRate() * 1000));
 }
 
 }  // namespace net