net/base/bandwidth_metrics.h

   1 // Copyright (c) 2011 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 #ifndef NET_BASE_BANDWIDTH_METRICS_H_
   6 #define NET_BASE_BANDWIDTH_METRICS_H_
   7
   8 #include <list>
   9
  10 #include "base/logging.h"
  11 #include "base/metrics/histogram.h"
  12 #include "base/time/time.h"
  13
  14 namespace net {
  15
  16 // Tracks statistics about the bandwidth metrics over time.  In order to
  17 // measure, this class needs to know when individual streams are in progress,
  18 // so that it can know when to discount idle time.  The BandwidthMetrics
  19 // is unidirectional - it should only be used to record upload or download
  20 // bandwidth, but not both.
  21 //
  22 // Note, the easiest thing to do is to just measure each stream and average
  23 // them or add them.  However, this does not work.  If multiple streams are in
  24 // progress concurrently, you have to look at the aggregate bandwidth at any
  25 // point in time.
  26 //
  27 //   Example:
  28 //      Imagine 4 streams opening and closing with overlapping time.
  29 //      We can't measure bandwidth by looking at any individual stream.
  30 //      We can only measure actual bandwidth by looking at the bandwidth
  31 //      across all open streams.
  32 //
  33 //         Time --------------------------------------->
  34 //         s1 +----------------+
  35 //         s2              +----------------+
  36 //         s3                            +--------------+
  37 //         s4                            +--------------+
  38 //
  39 // Example usage:
  40 //
  41 //   BandwidthMetrics tracker;
  42 //
  43 //   // When a stream is created
  44 //   tracker.StartStream();
  45 //
  46 //   // When data is transferred on any stream
  47 //   tracker.RecordSample(bytes);
  48 //
  49 //   // When the stream is finished
  50 //   tracker.StopStream();
  51 //
  52 // NOTE: This class is not thread safe.
  53 //
  54 class BandwidthMetrics {
  55  public:
  56   BandwidthMetrics()
  57       : num_streams_in_progress_(0),
  58         num_data_samples_(0),
  59         data_sum_(0.0),
  60         bytes_since_last_start_(0) {
  61   }
  62
  63   // Get the bandwidth.  Returns Kbps (kilo-bits-per-second).
  64   double bandwidth() const {
  65     return data_sum_ / num_data_samples_;
  66   }
  67
  68   // Record that we've started a stream.
  69   void StartStream() {
  70     // If we're the only stream, we've finished some idle time.  Record a new
  71     // timestamp to indicate the start of data flow.
  72     if (++num_streams_in_progress_ == 1) {
  73       last_start_ = base::TimeTicks::HighResNow();
  74       bytes_since_last_start_ = 0;
  75     }
  76   }
  77
  78   // Track that we've completed a stream.
  79   void StopStream() {
  80     if (--num_streams_in_progress_ == 0) {
  81       // We don't use small streams when tracking bandwidth because they are not
  82       // precise; imagine a 25 byte stream.  The sample is too small to make
  83       // a good measurement.
  84       // 20KB is an arbitrary value.  We might want to use a lesser value.
  85       static const int64 kRecordSizeThreshold = 20 * 1024;
  86       if (bytes_since_last_start_ < kRecordSizeThreshold)
  87         return;
  88
  89       base::TimeDelta delta = base::TimeTicks::HighResNow() - last_start_;
  90       double ms = delta.InMillisecondsF();
  91       if (ms > 0.0) {
  92         double kbps = static_cast<double>(bytes_since_last_start_) * 8 / ms;
  93         ++num_data_samples_;
  94         data_sum_ += kbps;
  95         VLOG(1) << "Bandwidth: " << kbps
  96                 << "Kbps (avg " << bandwidth() << "Kbps)";
  97         int kbps_int = static_cast<int>(kbps);
  98         UMA_HISTOGRAM_COUNTS_10000("Net.DownloadBandwidth", kbps_int);
  99       }
 100     }
 101   }
 102
 103   // Add a sample of the number of bytes read from the network into the tracker.
 104   void RecordBytes(int bytes) {
 105     DCHECK(num_streams_in_progress_);
 106     bytes_since_last_start_ += static_cast<int64>(bytes);
 107   }
 108
 109  private:
 110   int num_streams_in_progress_;   // The number of streams in progress.
 111   // TODO(mbelshe): Use a rolling buffer of 30 samples instead of an average.
 112   int num_data_samples_;          // The number of samples collected.
 113   double data_sum_;               // The sum of all samples collected.
 114   int64 bytes_since_last_start_;  // Bytes tracked during this "session".
 115   base::TimeTicks last_start_;    // Timestamp of the begin of this "session".
 116 };
 117
 118 // A utility class for managing the lifecycle of a measured stream.
 119 // It is important that we not leave unclosed streams, and this class helps
 120 // ensure we always stop them.
 121 class ScopedBandwidthMetrics {
 122  public:
 123   ScopedBandwidthMetrics();
 124   ~ScopedBandwidthMetrics();
 125
 126   void StartStream();
 127   void StopStream();
 128   void RecordBytes(int bytes);
 129
 130  private:
 131   bool started_;
 132 };
 133
 134 }  // namespace net
 135
 136 #endif  // NET_BASE_BANDWIDTH_METRICS_H_