cc: Heuristic for Renderer latency recovery

cc/scheduler/scheduler.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/scheduler/scheduler.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
@@ skipping 111 matching lines @@
 
 base::TimeTicks Scheduler::Now() const {
   base::TimeTicks now = gfx::FrameTime::Now();
   TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler.now"),
                "Scheduler::Now",
                "now",
                now);
   return now;
 }
 
+void Scheduler::SetAuthoritativeVSyncInterval(const base::TimeDelta& interval) {
+  authoritative_vsync_interval_ = interval;
+  if (vsync_observer_)
+    vsync_observer_->OnUpdateVSyncParameters(last_vsync_timebase_, interval);
+}
+
 void Scheduler::CommitVSyncParameters(base::TimeTicks timebase,
                                       base::TimeDelta interval) {
+  TRACE_EVENT2("cc", "Scheduler::CommitVSyncParameters", "timebase",
+               (timebase - base::TimeTicks()).InSecondsF(), "interval",
+               interval.InSecondsF());
+
   if (authoritative_vsync_interval_ != base::TimeDelta()) {
     interval = authoritative_vsync_interval_;
   } else if (interval == base::TimeDelta()) {
     // TODO(brianderson): We should not be receiving 0 intervals.
     interval = BeginFrameArgs::DefaultInterval();
   }
 
   last_vsync_timebase_ = timebase;
 
   if (vsync_observer_)
@@ skipping 236 matching lines @@
     BeginImplFrameWithDeadline(adjusted_args);
   }
   return true;
 }
 
 void Scheduler::SetChildrenNeedBeginFrames(bool children_need_begin_frames) {
   state_machine_.SetChildrenNeedBeginFrames(children_need_begin_frames);
   ProcessScheduledActions();
 }
 
-void Scheduler::SetAuthoritativeVSyncInterval(const base::TimeDelta& interval) {
-  authoritative_vsync_interval_ = interval;
-  if (vsync_observer_)
-    vsync_observer_->OnUpdateVSyncParameters(last_vsync_timebase_, interval);
-}
-
 void Scheduler::SetVideoNeedsBeginFrames(bool video_needs_begin_frames) {
   state_machine_.SetVideoNeedsBeginFrames(video_needs_begin_frames);
   ProcessScheduledActions();
 }
 
 void Scheduler::OnDrawForOutputSurface() {
   DCHECK(settings_.using_synchronous_renderer_compositor);
   DCHECK_EQ(state_machine_.begin_impl_frame_state(),
             SchedulerStateMachine::BEGIN_IMPL_FRAME_STATE_IDLE);
   DCHECK(!BeginImplFrameDeadlinePending());
@@ skipping 85 matching lines @@
                args.AsValue(), "main_thread_is_high_latency",
                main_thread_is_in_high_latency_mode);
   TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler"),
                  "MainThreadLatency", main_thread_is_in_high_latency_mode);
 
   advance_commit_state_task_.Cancel();
 
   begin_impl_frame_args_ = args;
   begin_impl_frame_args_.deadline -= client_->DrawDurationEstimate();
 
-  if (!state_machine_.impl_latency_takes_priority() &&
-      main_thread_is_in_high_latency_mode &&
-      CanCommitAndActivateBeforeDeadline()) {
+  if (ShouldRecoverMainLatency()) {
+    TRACE_EVENT_INSTANT0("cc", "SkipBeginMainFrameToReduceLatency",
+                         TRACE_EVENT_SCOPE_THREAD);
     state_machine_.SetSkipNextBeginMainFrameToReduceLatency();
+  } else if (ShouldRecoverImplLatency()) {

[sunnyps, 2015/05/22 21:15:04]

Does it make sense to prioritize skipping impl frame first? I.e. if both impl
thread and main thread are in high latency and we know we cannot draw in time we
should skip the impl frame but not skip the main frame.

[brianderson, 2015/06/30 22:03:52]

I prioritize skipping the main frame first for two reasons:

1) ShouldRecoverMainLatency will be true when there is a touch handler and we
care about synchronization with the main thread. In that case, skipping an Impl
frame will not help with synchornization.

2) Skipping the impl frame then a main frame back-to-back will arguably be more
jarring than the other way around since there will be two janks (the swap after
the skipped impl frame has an impl-thread discontinuity and the swap after the
skipped main frame has an main-thread discontinuity) instead of one (the main
and impl discontinuities show up in the same swap).

+    TRACE_EVENT_INSTANT0("cc", "SkipBeginImplFrameToReduceLatency",
+                         TRACE_EVENT_SCOPE_THREAD);
+    ProcessScheduledActions();
+    return;

[sunnyps, 2015/05/22 21:15:05]

FinishImplFrame should be called here, right?

[brianderson, 2015/05/23 00:53:56]

Ah! I am missing a call to frame_source_->DidFinishFrame() - that would explain
why this didn't work well with the --disabe-gpu-vsync.

This completely skips calling the BeginImplFrame though - so I don't think I
need to do all of FinishImplFrame.

   }
 
   BeginImplFrame();
 
   // The deadline will be scheduled in ProcessScheduledActions.
   state_machine_.OnBeginImplFrameDeadlinePending();
   ProcessScheduledActions();
 }
 
 void Scheduler::BeginImplFrameSynchronous(const BeginFrameArgs& args) {
   TRACE_EVENT1("cc,benchmark", "Scheduler::BeginImplFrame", "args",
                args.AsValue());
   begin_impl_frame_args_ = args;
   BeginImplFrame();
+
   FinishImplFrame();
 }
 
 void Scheduler::FinishImplFrame() {
   state_machine_.OnBeginImplFrameIdle();
   ProcessScheduledActions();
 
   client_->DidFinishImplFrame();
   frame_source_->DidFinishFrame(begin_retro_frame_args_.size());
 }
@@ skipping 17 matching lines @@
 
 void Scheduler::ScheduleBeginImplFrameDeadline() {
   // The synchronous compositor does not post a deadline task.
   DCHECK(!settings_.using_synchronous_renderer_compositor);
 
   begin_impl_frame_deadline_task_.Cancel();
   begin_impl_frame_deadline_task_.Reset(begin_impl_frame_deadline_closure_);
 
   begin_impl_frame_deadline_mode_ =
       state_machine_.CurrentBeginImplFrameDeadlineMode();
-
   base::TimeTicks deadline;
   switch (begin_impl_frame_deadline_mode_) {
     case SchedulerStateMachine::BEGIN_IMPL_FRAME_DEADLINE_MODE_NONE:
       // No deadline.
       return;
     case SchedulerStateMachine::BEGIN_IMPL_FRAME_DEADLINE_MODE_IMMEDIATE:
       // We are ready to draw a new active tree immediately.
       // We don't use Now() here because it's somewhat expensive to call.
       deadline = base::TimeTicks();
       break;
@@ skipping 197 matching lines @@
   state->SetInteger("begin_retro_frame_args_", begin_retro_frame_args_.size());
   state->SetBoolean("begin_retro_frame_task_",
                     !begin_retro_frame_task_.IsCancelled());
   state->SetBoolean("begin_impl_frame_deadline_task_",
                     !begin_impl_frame_deadline_task_.IsCancelled());
   state->SetBoolean("advance_commit_state_task_",
                     !advance_commit_state_task_.IsCancelled());
   state->BeginDictionary("begin_impl_frame_args");
   begin_impl_frame_args_.AsValueInto(state);
   state->EndDictionary();
+  state->SetString("begin_impl_frame_deadline_mode_",
+                   SchedulerStateMachine::BeginImplFrameDeadlineModeToString(
+                       begin_impl_frame_deadline_mode_));
 
   base::TimeTicks now = Now();
   base::TimeTicks frame_time = begin_impl_frame_args_.frame_time;
   base::TimeTicks deadline = begin_impl_frame_args_.deadline;
   base::TimeDelta interval = begin_impl_frame_args_.interval;
   state->BeginDictionary("major_timestamps_in_ms");
   state->SetDouble("0_interval", interval.InMillisecondsF());
   state->SetDouble("1_now_to_deadline", (deadline - now).InMillisecondsF());
   state->SetDouble("2_frame_time_to_now", (now - frame_time).InMillisecondsF());
   state->SetDouble("3_frame_time_to_deadline",
@@ skipping 12 matching lines @@
                    client_->DrawDurationEstimate().InMillisecondsF());
   state->SetDouble(
       "begin_main_frame_to_commit_duration_estimate_ms",
       client_->BeginMainFrameToCommitDurationEstimate().InMillisecondsF());
   state->SetDouble(
       "commit_to_activate_duration_estimate_ms",
       client_->CommitToActivateDurationEstimate().InMillisecondsF());
   state->EndDictionary();
 }
 
+bool Scheduler::ShouldRecoverMainLatency() const {
+  if (!state_machine_.MainThreadIsInHighLatencyMode())
+    return false;
+
+  if (state_machine_.impl_latency_takes_priority())
+    return false;
+
+  return CanCommitAndActivateBeforeDeadline();
+}
+
+bool Scheduler::ShouldRecoverImplLatency() const {
+  if (!state_machine_.ImplThreadIsLikelyInHighLatencyMode())
+    return false;
+
+  bool frame_time_is_before_deadline =
+      begin_impl_frame_args_.frame_time < begin_impl_frame_args_.deadline;
+
+  SchedulerStateMachine::BeginImplFrameDeadlineMode
+      next_begin_impl_frame_deadline_mode =
+          state_machine_.CurrentBeginImplFrameDeadlineMode();
+  switch (next_begin_impl_frame_deadline_mode) {
+    case SchedulerStateMachine::BEGIN_IMPL_FRAME_DEADLINE_MODE_NONE:
+      return false;
+    case SchedulerStateMachine::BEGIN_IMPL_FRAME_DEADLINE_MODE_IMMEDIATE:
+      return frame_time_is_before_deadline;
+    case SchedulerStateMachine::BEGIN_IMPL_FRAME_DEADLINE_MODE_REGULAR:
+      return frame_time_is_before_deadline;
+    case SchedulerStateMachine::BEGIN_IMPL_FRAME_DEADLINE_MODE_LATE:
+      return CanCommitAndActivateBeforeDeadline();
+    case SchedulerStateMachine::
+        BEGIN_IMPL_FRAME_DEADLINE_MODE_BLOCKED_ON_READY_TO_DRAW:
+      return false;
+  }
+  NOTREACHED();
+  return false;
+}
+
 bool Scheduler::CanCommitAndActivateBeforeDeadline() const {
   // Check if the main thread computation and commit can be finished before the
   // impl thread's deadline.
   base::TimeTicks estimated_draw_time =
       begin_impl_frame_args_.frame_time +
       client_->BeginMainFrameToCommitDurationEstimate() +
       client_->CommitToActivateDurationEstimate();
 
-  TRACE_EVENT2(
-      TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler"),
-      "CanCommitAndActivateBeforeDeadline",
-      "time_left_after_drawing_ms",
-      (begin_impl_frame_args_.deadline - estimated_draw_time).InMillisecondsF(),
-      "state",
-      AsValue());
-
   return estimated_draw_time < begin_impl_frame_args_.deadline;
 }
 
 bool Scheduler::IsBeginMainFrameSentOrStarted() const {
   return (state_machine_.commit_state() ==
               SchedulerStateMachine::COMMIT_STATE_BEGIN_MAIN_FRAME_SENT ||
           state_machine_.commit_state() ==
               SchedulerStateMachine::COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED);
 }
 
 }  // namespace cc