viz: Remove perfect cadence restriction for display frequency.

We enforce that the display frequency chosen must be in perfect cadence
with the video playback rate. This doesn't allow the display to run at
30Hz with videos updating at 24Hz. Remove this restriction and choose
the display frequency closest to the desired playback rate.

R=dalecurtis@chromium.org

Bug: 976583, 1069662
Change-Id: Icaaf87f4164c198b5b8ab6e900eaaaf21d229951
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2143534
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758061}

components/viz/service/display/frame_rate_decider.cc

@@ -116,6 +116,11 @@ void FrameRateDecider::UpdatePreferredFrameIntervalIfNeeded() {
     }
 
     if (num_of_frame_sinks_with_fixed_interval < 2) {
+      TRACE_EVENT_INSTANT0(
+          "viz",
+          "FrameRateDecider::UpdatePreferredFrameIntervalIfNeeded - not enough "
+          "frame sinks to toggle",
+          TRACE_EVENT_SCOPE_THREAD);
       SetPreferredInterval(UnspecifiedFrameInterval());
       return;
     }
@@ -136,25 +141,20 @@ void FrameRateDecider::UpdatePreferredFrameIntervalIfNeeded() {
         min_frame_sink_interval,
         client_->GetPreferredFrameIntervalForFrameSinkId(frame_sink_id));
   }
+  TRACE_EVENT_INSTANT1("viz",
+                       "FrameRateDecider::UpdatePreferredFrameIntervalIfNeeded",
+                       TRACE_EVENT_SCOPE_THREAD, "min_frame_sink_interval",
+                       min_frame_sink_interval.InMillisecondsF());
 
   // If we don't have an explicit preference from the active frame sinks, then
   // we use a 0 value for preferred frame interval to let the framework pick the
   // ideal refresh rate.
   base::TimeDelta new_preferred_interval = UnspecifiedFrameInterval();
   if (min_frame_sink_interval != BeginFrameArgs::MinInterval()) {
-    constexpr float kMaxIntervalDelta = 0.05;
     for (auto supported_interval : supported_intervals_) {
-      // We only use a supported interval if it is in perfect cadence with the
-      // desired interval.
-      float delta_int = 0;
-      float delta = std::modf(min_frame_sink_interval.InMicrosecondsF() /
-                                  supported_interval.InMicrosecondsF(),
-                              &delta_int);
-      bool in_perfect_cadence =
-          delta < kMaxIntervalDelta || delta > (1 - kMaxIntervalDelta);
-      if (in_perfect_cadence && supported_interval > new_preferred_interval) {
-        // Make sure that we select the largest one in the
-        // |supported_intervals_| that meets the requirements
+      // Pick the display interval which is closest to the preferred interval.
+      if ((min_frame_sink_interval - supported_interval).magnitude() <
+          (min_frame_sink_interval - new_preferred_interval).magnitude()) {
         new_preferred_interval = supported_interval;
       }
     }
@@ -165,6 +165,10 @@ void FrameRateDecider::UpdatePreferredFrameIntervalIfNeeded() {
 
 void FrameRateDecider::SetPreferredInterval(
     base::TimeDelta new_preferred_interval) {
+  TRACE_EVENT_INSTANT1("viz", "FrameRateDecider::SetPreferredInterval",
+                       TRACE_EVENT_SCOPE_THREAD, "new_preferred_interval",
+                       new_preferred_interval.InMillisecondsF());
+
   if (new_preferred_interval == last_computed_preferred_frame_interval_) {
     num_of_frames_since_preferred_interval_changed_++;
   } else {

components/viz/service/display/frame_rate_decider_unittest.cc

@@ -222,7 +222,7 @@ TEST_F(FrameRateDeciderTest, OptimalFrameSinkIntervelIsPicked) {
     FrameRateDecider::ScopedAggregate scope(frame_rate_decider_.get());
     frame_rate_decider_->OnSurfaceWillBeDrawn(surface1);
   }
-  EXPECT_EQ(display_interval_, FrameRateDecider::UnspecifiedFrameInterval());
+  EXPECT_EQ(display_interval_, min_supported_interval * 2);
 
   UpdateFrame(surface2);
   {