net/quic/congestion_control/rtt_stats.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4 //
   5 // A convenience class to store rtt samples and calculate smoothed rtt.
   6
   7 #ifndef NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
   8 #define NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_
   9
  10 #include <algorithm>
  11
  12 #include "base/basictypes.h"
  13 #include "net/quic/quic_protocol.h"
  14 #include "net/quic/quic_time.h"
  15
  16 namespace net {
  17
  18 namespace test {
  19 class RttStatsPeer;
  20 }  // namespace test
  21
  22 class NET_EXPORT_PRIVATE RttStats {
  23  public:
  24   RttStats();
  25
  26   // Returns true if any RTT measurements have been made.
  27   bool HasUpdates() const;
  28
  29   // Updates the RTT from an incoming ack which is received |send_delta| after
  30   // the packet is sent and the peer reports the ack being delayed |ack_delay|.
  31   void UpdateRtt(QuicTime::Delta send_delta,
  32                  QuicTime::Delta ack_delay,
  33                  QuicTime now);
  34
  35   // Causes the smoothed_rtt to be increased to the latest_rtt if the latest_rtt
  36   // is larger. The mean deviation is increased to the most recent deviation if
  37   // it's larger.
  38   void ExpireSmoothedMetrics();
  39
  40   // Forces RttStats to sample a new recent min rtt within the next
  41   // |num_samples| UpdateRtt calls.
  42   void SampleNewRecentMinRtt(uint32 num_samples);
  43
  44   // Returns the EWMA smoothed RTT for the connection.
  45   // May return Zero if no valid updates have occurred.
  46   QuicTime::Delta smoothed_rtt() const {
  47     return smoothed_rtt_;
  48   }
  49
  50   int64 initial_rtt_us() const {
  51     return initial_rtt_us_;
  52   }
  53
  54   // Sets an initial RTT to be used for SmoothedRtt before any RTT updates.
  55   void set_initial_rtt_us(int64 initial_rtt_us) {
  56     if (initial_rtt_us <= 0) {
  57       LOG(DFATAL) << "Attempt to set initial rtt to <= 0.";
  58       return;
  59     }
  60     initial_rtt_us_ = initial_rtt_us;
  61   }
  62
  63   // The most recent rtt measurement.
  64   // May return Zero if no valid updates have occurred.
  65   QuicTime::Delta latest_rtt() const {
  66     return latest_rtt_;
  67   }
  68
  69   // Returns the min_rtt for the entire connection.
  70   // May return Zero if no valid updates have occurred.
  71   QuicTime::Delta min_rtt() const {
  72     return min_rtt_;
  73   }
  74
  75   // Returns the min_rtt since SampleNewRecentMinRtt has been called, or the
  76   // min_rtt for the entire connection if SampleNewMinRtt was never called.
  77   QuicTime::Delta recent_min_rtt() const {
  78     return recent_min_rtt_.rtt;
  79   }
  80
  81   QuicTime::Delta mean_deviation() const {
  82     return mean_deviation_;
  83   }
  84
  85   // Sets how old a recent min rtt sample can be.
  86   void set_recent_min_rtt_window(QuicTime::Delta recent_min_rtt_window) {
  87     recent_min_rtt_window_ = recent_min_rtt_window;
  88   }
  89
  90  private:
  91   friend class test::RttStatsPeer;
  92
  93   // Used to track a sampled RTT window.
  94   struct RttSample {
  95     RttSample() : rtt(QuicTime::Delta::Zero()), time(QuicTime::Zero()) { }
  96     RttSample(QuicTime::Delta rtt, QuicTime time) : rtt(rtt), time(time) { }
  97
  98     QuicTime::Delta rtt;
  99     QuicTime time;  // Time the rtt sample was recorded.
 100   };
 101
 102   // Implements the resampling algorithm and the windowed min rtt algorithm.
 103   void UpdateRecentMinRtt(QuicTime::Delta rtt_sample, QuicTime now);
 104
 105   QuicTime::Delta latest_rtt_;
 106   QuicTime::Delta min_rtt_;
 107   QuicTime::Delta smoothed_rtt_;
 108   // Mean RTT deviation during this session.
 109   // Approximation of standard deviation, the error is roughly 1.25 times
 110   // larger than the standard deviation, for a normally distributed signal.
 111   QuicTime::Delta mean_deviation_;
 112   int64 initial_rtt_us_;
 113
 114   RttSample new_min_rtt_;
 115   uint32 num_min_rtt_samples_remaining_;
 116
 117   // State variables for Kathleen Nichols MinRTT algorithm.
 118   QuicTime::Delta recent_min_rtt_window_;
 119   RttSample recent_min_rtt_;  // a in the windowed algorithm.
 120   RttSample half_window_rtt_;  // b in the sampled algorithm.
 121   RttSample quarter_window_rtt_;  // c in the sampled algorithm.
 122
 123   DISALLOW_COPY_AND_ASSIGN(RttStats);
 124 };
 125
 126 }  // namespace net
 127
 128 #endif  // NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_