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

net/quic/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/quic_connection_logger.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 751 matching lines @@
   int range_start = 0;
   for (int i = 1; i <= valid_bits_in_mask; ++i) {
     bits_so_far += bit_mask_of_packets & 1;
     bit_mask_of_packets >>= 1;
     DCHECK_LT(range_start + bits_so_far, kBoundingSampleInCumulativeHistogram);
     histogram->Add(range_start + bits_so_far);
     range_start += i + 1;
   }
 }
 
+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
   // 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_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 {
   if (largest_received_packet_sequence_number_ == 0)
     return;  // Connection was never used.
   RecordAggregatePacketLossRate();
 
   base::HistogramBase* is_not_ack_histogram =
       GetPacketSequenceNumberHistogram("IsNotAck_");
   base::HistogramBase* is_an_ack_histogram =
@@ skipping 55 matching lines @@
       continue;
     }
     // Record some overlapping patterns, to get a better picture, since this is
     // not very expensive.
     if (i % 3 == 0)
       six_packet_histogram->Add(recent_6_mask);
   }
 }
 
 }  // namespace net