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      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) {
     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   if (media_stream_counter == 0) {
     58     LOG(ERROR) << "glXGetSyncValuesOML should not return TRUE with a "
     59                << "media stream counter of 0.";
     60     return;
     61   }
     62 
     63   struct timespec real_time;
     64   struct timespec monotonic_time;
     65   clock_gettime(CLOCK_REALTIME, &real_time);
     66   clock_gettime(CLOCK_MONOTONIC, &monotonic_time);
     67 
     68   int64 real_time_in_microseconds =
     69       real_time.tv_sec * base::Time::kMicrosecondsPerSecond +
     70       real_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
     71   int64 monotonic_time_in_microseconds =
     72       monotonic_time.tv_sec * base::Time::kMicrosecondsPerSecond +
     73       monotonic_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
     74 
     75   // We need the time according to CLOCK_MONOTONIC, so if we've been given
     76   // a time from CLOCK_REALTIME, we need to convert.
     77   bool time_conversion_needed =
     78       llabs(system_time - real_time_in_microseconds) <
     79       llabs(system_time - monotonic_time_in_microseconds);
     80 
     81   if (time_conversion_needed)
     82     system_time += monotonic_time_in_microseconds - real_time_in_microseconds;
     83 
     84   // Return if |system_time| is more than 1 frames in the future.
     85   int64 interval_in_microseconds = last_good_interval_.InMicroseconds();
     86   if (system_time > monotonic_time_in_microseconds + interval_in_microseconds)
     87     return;
     88 
     89   // If |system_time| is slightly in the future, adjust it to the previous
     90   // frame and use the last frame counter to prevent issues in the callback.
     91   if (system_time > monotonic_time_in_microseconds) {
     92     system_time -= interval_in_microseconds;
     93     media_stream_counter--;
     94   }
     95   if (monotonic_time_in_microseconds - system_time >
     96       base::Time::kMicrosecondsPerSecond)
     97     return;
     98 
     99   timebase = base::TimeTicks::FromInternalValue(system_time);
    100 
    101   // Only need the previous calculated interval for our filtering.
    102   while (last_computed_intervals_.size() > 1)
    103     last_computed_intervals_.pop();
    104 
    105   int32 numerator, denominator;
    106   if (GetMscRate(&numerator, &denominator)) {
    107     last_computed_intervals_.push(base::TimeDelta::FromSeconds(denominator) /
    108                                   numerator);
    109   } else if (!last_timebase_.is_null()) {
    110     base::TimeDelta timebase_diff = timebase - last_timebase_;
    111     int64 counter_diff = media_stream_counter - last_media_stream_counter_;
    112     if (counter_diff > 0 && timebase > last_timebase_)
    113       last_computed_intervals_.push(timebase_diff / counter_diff);
    114   }
    115 
    116   if (last_computed_intervals_.size() == 2) {
    117     const base::TimeDelta& old_interval = last_computed_intervals_.front();
    118     const base::TimeDelta& new_interval = last_computed_intervals_.back();
    119 
    120     double relative_change =
    121         fabs(old_interval.InMillisecondsF() - new_interval.InMillisecondsF()) /
    122         new_interval.InMillisecondsF();
    123     if (relative_change < kRelativeIntervalDifferenceThreshold) {
    124       if (new_interval.InMicroseconds() < kMinVsyncIntervalUs ||
    125           new_interval.InMicroseconds() > kMaxVsyncIntervalUs) {
    126         LOG(FATAL) << "Calculated bogus refresh interval of "
    127                    << new_interval.InMicroseconds() << " us. "
    128                    << "Last time base of " << last_timebase_.ToInternalValue()
    129                    << " us. "
    130                    << "Current time base of " << timebase.ToInternalValue()
    131                    << " us. "
    132                    << "Last media stream count of "
    133                    << last_media_stream_counter_ << ". "
    134                    << "Current media stream count of " << media_stream_counter
    135                    << ".";
    136       } else {
    137         last_good_interval_ = new_interval;
    138       }
    139     }
    140   }
    141 
    142   last_timebase_ = timebase;
    143   last_media_stream_counter_ = media_stream_counter;
    144   callback.Run(timebase, last_good_interval_);
    145 #endif  // defined(OS_LINUX)
    146 }
    147 
    148 }  // namespace gfx
    149