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   QuicTime::Delta SmoothedRtt() const;
  45
  46   // Returns the min_rtt for the entire connection if a min has been measured.
  47   // This returns an initial non-zero RTT estimate if no measurements have yet
  48   // been made.
  49   QuicTime::Delta MinRtt() const;
  50
  51   int64 initial_rtt_us() const {
  52     return initial_rtt_us_;
  53   }
  54
  55   // Sets an initial RTT to be used for SmoothedRtt before any RTT updates.
  56   void set_initial_rtt_us(int64 initial_rtt_us) {
  57     initial_rtt_us_ = initial_rtt_us;
  58   }
  59
  60   QuicTime::Delta latest_rtt() const {
  61     return latest_rtt_;
  62   }
  63
  64   // Returns the min_rtt since SampleNewRecentMinRtt has been called, or the
  65   // min_rtt for the entire connection if SampleNewMinRtt was never called.
  66   QuicTime::Delta recent_min_rtt() const {
  67     return recent_min_rtt_.rtt;
  68   }
  69
  70   QuicTime::Delta mean_deviation() const {
  71     return mean_deviation_;
  72   }
  73
  74   // Sets how old a recent min rtt sample can be.
  75   void set_recent_min_rtt_window(QuicTime::Delta recent_min_rtt_window) {
  76     recent_min_rtt_window_ = recent_min_rtt_window;
  77   }
  78
  79  private:
  80   friend class test::RttStatsPeer;
  81
  82   // Used to track a sampled RTT window.
  83   struct RttSample {
  84     RttSample() : rtt(QuicTime::Delta::Zero()), time(QuicTime::Zero()) { }
  85     RttSample(QuicTime::Delta rtt, QuicTime time) : rtt(rtt), time(time) { }
  86
  87     QuicTime::Delta rtt;
  88     QuicTime time;  // Time the rtt sample was recorded.
  89   };
  90
  91   // Implements the resampling algorithm and the windowed min rtt algorithm.
  92   void UpdateRecentMinRtt(QuicTime::Delta rtt_sample, QuicTime now);
  93
  94   QuicTime::Delta latest_rtt_;
  95   QuicTime::Delta min_rtt_;
  96   QuicTime::Delta smoothed_rtt_;
  97   // Mean RTT deviation during this session.
  98   // Approximation of standard deviation, the error is roughly 1.25 times
  99   // larger than the standard deviation, for a normally distributed signal.
 100   QuicTime::Delta mean_deviation_;
 101   int64 initial_rtt_us_;
 102
 103   RttSample new_min_rtt_;
 104   uint32 num_min_rtt_samples_remaining_;
 105
 106   // State variables for Kathleen Nichols MinRTT algorithm.
 107   QuicTime::Delta recent_min_rtt_window_;
 108   RttSample recent_min_rtt_;  // a in the windowed algorithm.
 109   RttSample half_window_rtt_;  // b in the sampled algorithm.
 110   RttSample quarter_window_rtt_;  // c in the sampled algorithm.
 111
 112   DISALLOW_COPY_AND_ASSIGN(RttStats);
 113 };
 114
 115 }  // namespace net
 116
 117 #endif  // NET_QUIC_CONGESTION_CONTROL_RTT_STATS_H_