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      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
    139