cc/debug/frame_rate_counter.cc

   1 // Copyright 2012 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 #include "cc/debug/frame_rate_counter.h"
   6
   7 #include <algorithm>
   8 #include <limits>
   9
  10 #include "base/metrics/histogram.h"
  11 #include "cc/trees/proxy.h"
  12
  13 namespace cc {
  14
  15 // The following constants are measured in seconds.
  16
  17 // Two thresholds (measured in seconds) that describe what is considered to be a
  18 // "no-op frame" that should not be counted.
  19 // - if the frame is too fast, then given our compositor implementation, the
  20 // frame probably was a no-op and did not draw.
  21 // - if the frame is too slow, then there is probably not animating content, so
  22 // we should not pollute the average.
  23 static const double kFrameTooFast = 1.0 / 70.0;
  24 static const double kFrameTooSlow = 1.0 / 4.0;
  25
  26 // If a frame takes longer than this threshold (measured in seconds) then we
  27 // (naively) assume that it missed a screen refresh; that is, we dropped a
  28 // frame.
  29 // TODO(brianderson): Determine this threshold based on monitor refresh rate,
  30 // crbug.com/138642.
  31 static const double kDroppedFrameTime = 1.0 / 50.0;
  32
  33 // static
  34 scoped_ptr<FrameRateCounter> FrameRateCounter::Create(bool has_impl_thread) {
  35   return make_scoped_ptr(new FrameRateCounter(has_impl_thread));
  36 }
  37
  38 base::TimeDelta FrameRateCounter::RecentFrameInterval(size_t n) const {
  39   DCHECK_GT(n, 0u);
  40   DCHECK_LT(n, ring_buffer_.BufferSize());
  41   return ring_buffer_.ReadBuffer(n) - ring_buffer_.ReadBuffer(n - 1);
  42 }
  43
  44 FrameRateCounter::FrameRateCounter(bool has_impl_thread)
  45     : has_impl_thread_(has_impl_thread), dropped_frame_count_(0) {}
  46
  47 void FrameRateCounter::SaveTimeStamp(base::TimeTicks timestamp) {
  48   ring_buffer_.SaveToBuffer(timestamp);
  49
  50   // Check if frame interval can be computed.
  51   if (ring_buffer_.CurrentIndex() < 2)
  52     return;
  53
  54   base::TimeDelta frame_interval_seconds =
  55       RecentFrameInterval(ring_buffer_.BufferSize() - 1);
  56
  57   if (has_impl_thread_ && ring_buffer_.CurrentIndex() > 0) {
  58     UMA_HISTOGRAM_CUSTOM_COUNTS("Renderer4.CompositorThreadImplDrawDelay",
  59                                 frame_interval_seconds.InMilliseconds(),
  60                                 1,
  61                                 120,
  62                                 60);
  63   }
  64
  65   if (!IsBadFrameInterval(frame_interval_seconds) &&
  66       frame_interval_seconds.InSecondsF() > kDroppedFrameTime)
  67     ++dropped_frame_count_;
  68 }
  69
  70 bool FrameRateCounter::IsBadFrameInterval(
  71     base::TimeDelta interval_between_consecutive_frames) const {
  72   double delta = interval_between_consecutive_frames.InSecondsF();
  73   bool scheduler_allows_double_frames = !has_impl_thread_;
  74   bool interval_too_fast =
  75       scheduler_allows_double_frames ? delta < kFrameTooFast : delta <= 0.0;
  76   bool interval_too_slow = delta > kFrameTooSlow;
  77   return interval_too_fast || interval_too_slow;
  78 }
  79
  80 void FrameRateCounter::GetMinAndMaxFPS(double* min_fps, double* max_fps) const {
  81   *min_fps = std::numeric_limits<double>::max();
  82   *max_fps = 0.0;
  83
  84   for (RingBufferType::Iterator it = --ring_buffer_.End(); it; --it) {
  85     base::TimeDelta delta = RecentFrameInterval(it.index() + 1);
  86
  87     if (IsBadFrameInterval(delta))
  88       continue;
  89
  90     DCHECK_GT(delta.InSecondsF(), 0.f);
  91     double fps = 1.0 / delta.InSecondsF();
  92
  93     *min_fps = std::min(fps, *min_fps);
  94     *max_fps = std::max(fps, *max_fps);
  95   }
  96
  97   if (*min_fps > *max_fps)
  98     *min_fps = *max_fps;
  99 }
 100
 101 double FrameRateCounter::GetAverageFPS() const {
 102   int frame_count = 0;
 103   double frame_times_total = 0.0;
 104   double average_fps = 0.0;
 105
 106   // Walk backwards through the samples looking for a run of good frame
 107   // timings from which to compute the mean.
 108   //
 109   // Slow frames occur just because the user is inactive, and should be
 110   // ignored. Fast frames are ignored if the scheduler is in single-thread
 111   // mode in order to represent the true frame rate in spite of the fact that
 112   // the first few swapbuffers happen instantly which skews the statistics
 113   // too much for short lived animations.
 114   //
 115   // IsBadFrameInterval encapsulates the frame too slow/frame too fast logic.
 116
 117   for (RingBufferType::Iterator it = --ring_buffer_.End();
 118        it && frame_times_total < 1.0;
 119        --it) {
 120     base::TimeDelta delta = RecentFrameInterval(it.index() + 1);
 121
 122     if (!IsBadFrameInterval(delta)) {
 123       frame_count++;
 124       frame_times_total += delta.InSecondsF();
 125     } else if (frame_count) {
 126       break;
 127     }
 128   }
 129
 130   if (frame_count) {
 131     DCHECK_GT(frame_times_total, 0.0);
 132     average_fps = frame_count / frame_times_total;
 133   }
 134
 135   return average_fps;
 136 }
 137
 138 }  // namespace cc