ui/gl/sync_control_vsync_provider.cc

   1 // Copyright 2013 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 "ui/gl/sync_control_vsync_provider.h"
   6
   7 #include <math.h>
   8
   9 #include "base/logging.h"
  10 #include "base/time/time.h"
  11
  12 #if defined(OS_LINUX)
  13 // These constants define a reasonable range for a calculated refresh interval.
  14 // Calculating refreshes out of this range will be considered a fatal error.
  15 const int64 kMinVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 400;
  16 const int64 kMaxVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 10;
  17
  18 // How much noise we'll tolerate between successive computed intervals before
  19 // we think the latest computed interval is invalid (noisey due to
  20 // monitor configuration change, moving a window between monitors, etc.).
  21 const double kRelativeIntervalDifferenceThreshold = 0.05;
  22 #endif
  23
  24 namespace gfx {
  25
  26 SyncControlVSyncProvider::SyncControlVSyncProvider()
  27     : VSyncProvider(), last_media_stream_counter_(0), invalid_msc_(false) {
  28   // On platforms where we can't get an accurate reading on the refresh
  29   // rate we fall back to the assumption that we're displaying 60 frames
  30   // per second.
  31   last_good_interval_ = base::TimeDelta::FromSeconds(1) / 60;
  32 }
  33
  34 SyncControlVSyncProvider::~SyncControlVSyncProvider() {}
  35
  36 void SyncControlVSyncProvider::GetVSyncParameters(
  37     const UpdateVSyncCallback& callback) {
  38 #if defined(OS_LINUX)
  39   base::TimeTicks timebase;
  40
  41   // The actual clock used for the system time returned by glXGetSyncValuesOML
  42   // is unspecified. In practice, the clock used is likely to be either
  43   // CLOCK_REALTIME or CLOCK_MONOTONIC, so we compare the returned time to the
  44   // current time according to both clocks, and assume that the returned time
  45   // was produced by the clock whose current time is closest to it, subject
  46   // to the restriction that the returned time must not be in the future
  47   // (since it is the time of a vblank that has already occurred).
  48   int64 system_time;
  49   int64 media_stream_counter;
  50   int64 swap_buffer_counter;
  51   if (!GetSyncValues(&system_time, &media_stream_counter, &swap_buffer_counter))
  52     return;
  53
  54   // Both Intel and Mali drivers will return TRUE for GetSyncValues
  55   // but a value of 0 for MSC if they cannot access the CRTC data structure
  56   // associated with the surface. crbug.com/231945
  57   bool prev_invalid_msc = invalid_msc_;
  58   invalid_msc_ = (media_stream_counter == 0);
  59   if (invalid_msc_) {
  60     LOG_IF(ERROR, !prev_invalid_msc) << "glXGetSyncValuesOML "
  61         "should not return TRUE with a media stream counter of 0.";
  62     return;
  63   }
  64
  65   struct timespec real_time;
  66   struct timespec monotonic_time;
  67   clock_gettime(CLOCK_REALTIME, &real_time);
  68   clock_gettime(CLOCK_MONOTONIC, &monotonic_time);
  69
  70   int64 real_time_in_microseconds =
  71       real_time.tv_sec * base::Time::kMicrosecondsPerSecond +
  72       real_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
  73   int64 monotonic_time_in_microseconds =
  74       monotonic_time.tv_sec * base::Time::kMicrosecondsPerSecond +
  75       monotonic_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
  76
  77   // We need the time according to CLOCK_MONOTONIC, so if we've been given
  78   // a time from CLOCK_REALTIME, we need to convert.
  79   bool time_conversion_needed =
  80       llabs(system_time - real_time_in_microseconds) <
  81       llabs(system_time - monotonic_time_in_microseconds);
  82
  83   if (time_conversion_needed)
  84     system_time += monotonic_time_in_microseconds - real_time_in_microseconds;
  85
  86   // Return if |system_time| is more than 1 frames in the future.
  87   int64 interval_in_microseconds = last_good_interval_.InMicroseconds();
  88   if (system_time > monotonic_time_in_microseconds + interval_in_microseconds)
  89     return;
  90
  91   // If |system_time| is slightly in the future, adjust it to the previous
  92   // frame and use the last frame counter to prevent issues in the callback.
  93   if (system_time > monotonic_time_in_microseconds) {
  94     system_time -= interval_in_microseconds;
  95     media_stream_counter--;
  96   }
  97   if (monotonic_time_in_microseconds - system_time >
  98       base::Time::kMicrosecondsPerSecond)
  99     return;
 100
 101   timebase = base::TimeTicks::FromInternalValue(system_time);
 102
 103   // Only need the previous calculated interval for our filtering.
 104   while (last_computed_intervals_.size() > 1)
 105     last_computed_intervals_.pop();
 106
 107   int32 numerator, denominator;
 108   if (GetMscRate(&numerator, &denominator)) {
 109     last_computed_intervals_.push(base::TimeDelta::FromSeconds(denominator) /
 110                                   numerator);
 111   } else if (!last_timebase_.is_null()) {
 112     base::TimeDelta timebase_diff = timebase - last_timebase_;
 113     int64 counter_diff = media_stream_counter - last_media_stream_counter_;
 114     if (counter_diff > 0 && timebase > last_timebase_)
 115       last_computed_intervals_.push(timebase_diff / counter_diff);
 116   }
 117
 118   if (last_computed_intervals_.size() == 2) {
 119     const base::TimeDelta& old_interval = last_computed_intervals_.front();
 120     const base::TimeDelta& new_interval = last_computed_intervals_.back();
 121
 122     double relative_change =
 123         fabs(old_interval.InMillisecondsF() - new_interval.InMillisecondsF()) /
 124         new_interval.InMillisecondsF();
 125     if (relative_change < kRelativeIntervalDifferenceThreshold) {
 126       if (new_interval.InMicroseconds() < kMinVsyncIntervalUs ||
 127           new_interval.InMicroseconds() > kMaxVsyncIntervalUs) {
 128 #if defined(USE_ASH)
 129         // On ash platforms (ChromeOS essentially), the real refresh interval is
 130         // queried from XRandR, regardless of the value calculated here, and
 131         // this value is overriden by ui::CompositorVSyncManager.  The log
 132         // should not be fatal in this case. Reconsider all this when XRandR
 133         // support is added to non-ash platforms.
 134         // http://crbug.com/340851
 135         LOG(ERROR)
 136 #else
 137         LOG(FATAL)
 138 #endif  // USE_ASH
 139             << "Calculated bogus refresh interval="
 140             << new_interval.InMicroseconds()
 141             << " us., last_timebase_=" << last_timebase_.ToInternalValue()
 142             << " us., timebase=" << timebase.ToInternalValue()
 143             << " us., last_media_stream_counter_=" << last_media_stream_counter_
 144             << ", media_stream_counter=" << media_stream_counter;
 145       } else {
 146         last_good_interval_ = new_interval;
 147       }
 148     }
 149   }
 150
 151   last_timebase_ = timebase;
 152   last_media_stream_counter_ = media_stream_counter;
 153   callback.Run(timebase, last_good_interval_);
 154 #endif  // defined(OS_LINUX)
 155 }
 156
 157 }  // namespace gfx