QUIC - disable QUIC if packet loss rate is bad for a connection.

net/quic/quic_connection_logger.cc

Index: net/quic/quic_connection_logger.cc
diff --git a/net/quic/quic_connection_logger.cc b/net/quic/quic_connection_logger.cc
index 2005b88165a6fe14d01db79edf278204689afa4b..4fb53725cc681dc73b02582bea7fa11755f7440e 100644
--- a/net/quic/quic_connection_logger.cc
+++ b/net/quic/quic_connection_logger.cc
@@ -769,6 +769,19 @@ void QuicConnectionLogger::AddTo21CumulativeHistogram(
   }
 }
 
+float QuicConnectionLogger::PacketLossRate() const {

[Ryan Hamilton, 2015/03/23 02:31:06]

This is the received packet loss rate, right? (As opposed to the sent packet
loss rate). We should probably put it into the method name.

[ramant (doing other things), 2015/03/24 03:07:22]

Done.

+  // Never received a packet from server, very lossy connection?
+  if (largest_received_packet_sequence_number_ == 0)
+    return 1000.0f;
+  QuicPacketSequenceNumber divisor = largest_received_packet_sequence_number_;
+  QuicPacketSequenceNumber numerator = divisor - num_packets_received_;
+  if (divisor < 100000)
+    numerator *= 1000;
+  else
+    divisor /= 1000;
+  return numerator / divisor;

[Ryan Hamilton, 2015/03/23 02:31:06]

So the reason this code uses * 1000 or / 1000 is because it was going directly
into a histogram as an int. Since you're returning a float, I think you can just
do x / y and then multiply by 1000 down at line 799 when adding to the
histogram.

[ramant (doing other things), 2015/03/24 03:07:22]

Done.

+}
+
 void QuicConnectionLogger::RecordAggregatePacketLossRate() const {
   // For short connections under 22 packets in length, we'll rely on the
   // Net.QuicSession.21CumulativePacketsReceived_* histogram to indicate packet
@@ -779,17 +792,11 @@ void QuicConnectionLogger::RecordAggregatePacketLossRate() const {
   if (largest_received_packet_sequence_number_ <= 21)
     return;
 
-  QuicPacketSequenceNumber divisor = largest_received_packet_sequence_number_;
-  QuicPacketSequenceNumber numerator = divisor - num_packets_received_;
-  if (divisor < 100000)
-    numerator *= 1000;
-  else
-    divisor /= 1000;
   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>(numerator / divisor));
+  histogram->Add(static_cast<base::HistogramBase::Sample>(PacketLossRate()));
 }
 
 void QuicConnectionLogger::RecordLossHistograms() const {