cc: Heuristic for Renderer latency recovery

cc/scheduler/scheduler_unittest.cc

Index: cc/scheduler/scheduler_unittest.cc
diff --git a/cc/scheduler/scheduler_unittest.cc b/cc/scheduler/scheduler_unittest.cc
index 29505e5a9b76197de307feae951fb44f0565c5c0..9e361b917b8d61c69958b9cf16a515e66f6af20d 100644
--- a/cc/scheduler/scheduler_unittest.cc
+++ b/cc/scheduler/scheduler_unittest.cc
@@ -246,6 +246,16 @@ class SchedulerTest : public testing::Test {
         fake_compositor_timing_history.Pass());
     DCHECK(scheduler_);
     client_->set_scheduler(scheduler_.get());
+
+    // Use large estimates by default to avoid latency recovery
+    // in most tests.
+    base::TimeDelta one_second = base::TimeDelta::FromSeconds(1);
+    fake_compositor_timing_history_->SetBeginMainFrameToCommitDurationEstimate(
+        one_second);
+    fake_compositor_timing_history_->SetCommitToReadyToActivateDurationEstimate(
+        one_second);
+    fake_compositor_timing_history_->SetDrawDurationEstimate(one_second);
+
     return scheduler_.get();
   }
 
@@ -384,11 +394,9 @@ class SchedulerTest : public testing::Test {
     return fake_external_begin_frame_source_.get();
   }
 
-  void MainFrameInHighLatencyMode(
-      int64 begin_main_frame_to_commit_estimate_in_ms,
-      int64 commit_to_activate_estimate_in_ms,
-      bool impl_latency_takes_priority,
-      bool should_send_begin_main_frame);
+  void CheckMainFrameSkippedAfterLateCommit(bool expect_send_begin_main_frame);
+  void ImplFrameSkippedAfterLateSwapAck(bool swap_ack_before_deadline);
+  void ImplFrameIsNotSkippedAfterLateSwapAck();
   void BeginFramesNotFromClient(bool use_external_begin_frame_source,
                                 bool throttle_frame_production);
   void BeginFramesNotFromClient_SwapThrottled(
@@ -1289,24 +1297,8 @@ TEST_F(SchedulerTest, WaitForReadyToDrawCancelledWhenLostOutputSurface) {
   EXPECT_ACTION("SendBeginMainFrameNotExpectedSoon", client_, 2, 3);
 }
 
-void SchedulerTest::MainFrameInHighLatencyMode(
-    int64 begin_main_frame_to_commit_estimate_in_ms,
-    int64 commit_to_activate_estimate_in_ms,
-    bool impl_latency_takes_priority,
-    bool should_send_begin_main_frame) {
-  scheduler_settings_.use_external_begin_frame_source = true;
-  SetUpScheduler(true);
-
-  fake_compositor_timing_history_->SetBeginMainFrameToCommitDurationEstimate(
-      base::TimeDelta::FromMilliseconds(
-          begin_main_frame_to_commit_estimate_in_ms));
-  fake_compositor_timing_history_->SetCommitToReadyToActivateDurationEstimate(
-      base::TimeDelta::FromMilliseconds(commit_to_activate_estimate_in_ms));
-  fake_compositor_timing_history_->SetDrawDurationEstimate(
-      base::TimeDelta::FromMilliseconds(1));
-
-  scheduler_->SetImplLatencyTakesPriority(impl_latency_takes_priority);
-
+void SchedulerTest::CheckMainFrameSkippedAfterLateCommit(
+    bool expect_send_begin_main_frame) {
   // Impl thread hits deadline before commit finishes.
   scheduler_->SetNeedsCommit();
   EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
@@ -1326,36 +1318,421 @@ void SchedulerTest::MainFrameInHighLatencyMode(
   EXPECT_SCOPED(AdvanceFrame());
   EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
   task_runner().RunPendingTasks();  // Run posted deadline.
-  EXPECT_EQ(scheduler_->MainThreadIsInHighLatencyMode(),
-            should_send_begin_main_frame);
-  EXPECT_EQ(client_->HasAction("ScheduledActionSendBeginMainFrame"),
-            should_send_begin_main_frame);
+  EXPECT_EQ(expect_send_begin_main_frame,
+            scheduler_->MainThreadIsInHighLatencyMode());
+  EXPECT_EQ(expect_send_begin_main_frame,
+            client_->HasAction("ScheduledActionSendBeginMainFrame"));
+}
+
+TEST_F(SchedulerTest, MainFrameSkippedAfterLateCommit) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+
+  bool expect_send_begin_main_frame = false;
+  EXPECT_SCOPED(
+      CheckMainFrameSkippedAfterLateCommit(expect_send_begin_main_frame));
 }
 
 TEST_F(SchedulerTest,
-       SkipMainFrameIfHighLatencyAndCanCommitAndActivateBeforeDeadline) {
-  // Set up client so that estimates indicate that we can commit and activate
-  // before the deadline (~8ms by default).
-  EXPECT_SCOPED(MainFrameInHighLatencyMode(1, 1, false, false));
+       MainFrameNotSkippedAfterLateCommitInPreferImplLatencyMode) {

[sunnyps, 2015/07/08 22:37:13]

This test should be generalized - we want to check that we don't skip a
BeginMainFrame if we're not waiting for it to draw. There are conditions other
than impl latency takes priority that affect whether we wait to draw or not e.g.
active_tree_needs_first_draw. See
ShouldTriggerBeginImplFrameDeadlineImmediately.

[brianderson, 2015/07/09 01:28:11]

Not sure if this needs to be generalized. See my comment on
Scheduler::ShouldRecoverMainLatency.

+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  scheduler_->SetImplLatencyTakesPriority(true);
+
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+
+  bool expect_send_begin_main_frame = true;
+  EXPECT_SCOPED(
+      CheckMainFrameSkippedAfterLateCommit(expect_send_begin_main_frame));
 }
 
-TEST_F(SchedulerTest, NotSkipMainFrameIfHighLatencyAndCanCommitTooLong) {
-  // Set up client so that estimates indicate that the commit cannot finish
-  // before the deadline (~8ms by default).
-  EXPECT_SCOPED(MainFrameInHighLatencyMode(10, 1, false, true));
+TEST_F(SchedulerTest,
+       MainFrameNotSkippedAfterLateCommit_CommitEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetBeginMainFrameToCommitDurationEstimate(
+      slow_duration);
+
+  bool expect_send_begin_main_frame = true;
+  EXPECT_SCOPED(
+      CheckMainFrameSkippedAfterLateCommit(expect_send_begin_main_frame));
 }
 
-TEST_F(SchedulerTest, NotSkipMainFrameIfHighLatencyAndCanActivateTooLong) {
-  // Set up client so that estimates indicate that the activate cannot finish
-  // before the deadline (~8ms by default).
-  EXPECT_SCOPED(MainFrameInHighLatencyMode(1, 10, false, true));
+TEST_F(SchedulerTest,
+       MainFrameNotSkippedAfterLateCommit_ReadyToActivateEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetCommitToReadyToActivateDurationEstimate(
+      slow_duration);
+
+  bool expect_send_begin_main_frame = true;
+  EXPECT_SCOPED(
+      CheckMainFrameSkippedAfterLateCommit(expect_send_begin_main_frame));
+}
+
+TEST_F(SchedulerTest,
+       MainFrameNotSkippedAfterLateCommit_ActivateEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetActivateDurationEstimate(slow_duration);
+
+  bool expect_send_begin_main_frame = true;
+  EXPECT_SCOPED(
+      CheckMainFrameSkippedAfterLateCommit(expect_send_begin_main_frame));
+}
+
+TEST_F(SchedulerTest, MainFrameNotSkippedAfterLateCommit_DrawEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetDrawDurationEstimate(slow_duration);
+
+  bool expect_send_begin_main_frame = true;
+  EXPECT_SCOPED(
+      CheckMainFrameSkippedAfterLateCommit(expect_send_begin_main_frame));
+}
+
+void SchedulerTest::ImplFrameSkippedAfterLateSwapAck(
+    bool swap_ack_before_deadline) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+
+  // Use estimates that indicate commit and activate can finish before the
+  // deadline.

[sunnyps, 2015/07/08 22:37:13]

nit: Move setting the estimates to the test - so that it looks like the other
tests.

[brianderson, 2015/07/09 01:28:11]

Done.

+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+
+  // To get into a high latency state, this test disables automatic swap acks.
+  scheduler_->SetMaxSwapsPending(1);
+  client_->SetAutomaticSwapAck(false);
+
+  // Draw and swap for first BeginFrame
+  client_->Reset();
+  scheduler_->SetNeedsCommit();
+  scheduler_->SetNeedsRedraw();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  SendNextBeginFrame();
+  EXPECT_ACTION("SetNeedsBeginFrames(true)", client_, 0, 4);
+  EXPECT_ACTION("WillBeginImplFrame", client_, 1, 4);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 2, 4);
+  EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 3, 4);
+
+  client_->Reset();
+  scheduler_->NotifyBeginMainFrameStarted();
+  scheduler_->NotifyReadyToCommit();
+  scheduler_->NotifyReadyToActivate();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  EXPECT_ACTION("ScheduledActionCommit", client_, 0, 4);
+  EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 1, 4);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 2, 4);
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 3, 4);
+
+  // Verify we skip every other frame if the swap ack consistently
+  // comes back late.
+  for (int i = 0; i < 10; i++) {
+    // Not calling scheduler_->DidSwapBuffersComplete() until after next
+    // BeginImplFrame puts the impl thread in high latency mode.
+    client_->Reset();
+    scheduler_->SetNeedsCommit();
+    scheduler_->SetNeedsRedraw();
+    EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+    SendNextBeginFrame();
+    // Verify that we skip the BeginImplFrame
+    EXPECT_NO_ACTION(client_);
+    EXPECT_FALSE(scheduler_->BeginImplFrameDeadlinePending());
+    EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+
+    // Verify that we do not perform any actions after we are no longer
+    // swap throttled.
+    client_->Reset();
+    if (swap_ack_before_deadline) {
+      // It shouldn't matter if the swap ack comes back before the deadline...
+      scheduler_->DidSwapBuffersComplete();
+      task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+    } else {
+      // ... or after the deadline.
+      task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+      scheduler_->DidSwapBuffersComplete();
+    }
+    EXPECT_NO_ACTION(client_);
+
+    // Verify that we start the next BeginImplFrame and continue normally
+    // after having just skipped a BeginImplFrame.
+    client_->Reset();
+    EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+    scheduler_->SetNeedsCommit();

[sunnyps, 2015/07/08 22:37:13]

Shouldn't need to call SetNeedsCommit or SetNeedsRedraw again. Also
SetNeedsRedraw is redundant - activation will set the needs_redraw flag.

[brianderson, 2015/07/09 01:28:12]

Ah, these calls are redundant. Will remove them.

I'd like to keep the SetNeedsRedraw() above though in case the scheduler tries
to swap outside of the BeginImplFrame before we get a new active tree.

This isn't a problem with the current approach, but was an issue I ran into with
my original approach and could be something to protect against if we decouple
draws from the deadline.

+    scheduler_->SetNeedsRedraw();
+    SendNextBeginFrame();
+    EXPECT_ACTION("WillBeginImplFrame", client_, 0, 3);
+    EXPECT_ACTION("ScheduledActionAnimate", client_, 1, 3);
+    EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 2, 3);
+
+    client_->Reset();
+    scheduler_->NotifyBeginMainFrameStarted();
+    scheduler_->NotifyReadyToCommit();
+    scheduler_->NotifyReadyToActivate();
+    task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+    EXPECT_ACTION("ScheduledActionCommit", client_, 0, 4);
+    EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 1, 4);
+    EXPECT_ACTION("ScheduledActionAnimate", client_, 2, 4);
+    EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 3, 4);
+  }
+}
+
+TEST_F(SchedulerTest, ImplFrameSkippedAfterLateSwapAck_SwapAckThenDeadline) {
+  bool swap_ack_before_deadline = true;
+  EXPECT_SCOPED(ImplFrameSkippedAfterLateSwapAck(swap_ack_before_deadline));
+}
+
+TEST_F(SchedulerTest, ImplFrameSkippedAfterLateSwapAck_DeadlineThenSwapAck) {
+  bool swap_ack_before_deadline = false;
+  EXPECT_SCOPED(ImplFrameSkippedAfterLateSwapAck(swap_ack_before_deadline));
+}
+
+void SchedulerTest::ImplFrameIsNotSkippedAfterLateSwapAck() {
+  // To get into a high latency state, this test disables automatic swap acks.
+  scheduler_->SetMaxSwapsPending(1);
+  client_->SetAutomaticSwapAck(false);
+
+  // Draw and swap for first BeginFrame
+  client_->Reset();
+  scheduler_->SetNeedsCommit();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  SendNextBeginFrame();
+  EXPECT_ACTION("SetNeedsBeginFrames(true)", client_, 0, 3);
+  EXPECT_ACTION("WillBeginImplFrame", client_, 1, 3);
+  EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 2, 3);
+
+  client_->Reset();
+  scheduler_->NotifyBeginMainFrameStarted();
+  scheduler_->NotifyReadyToCommit();
+  scheduler_->NotifyReadyToActivate();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  EXPECT_ACTION("ScheduledActionCommit", client_, 0, 4);
+  EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 1, 4);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 2, 4);
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 3, 4);
+
+  // Verify impl thread consistently operates in high latency mode
+  // without skipping any frames.
+  for (int i = 0; i < 10; i++) {
+    // Not calling scheduler_->DidSwapBuffersComplete() until after next frame
+    // puts the impl thread in high latency mode.
+    client_->Reset();
+    scheduler_->SetNeedsCommit();
+    EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+    SendNextBeginFrame();
+    EXPECT_SINGLE_ACTION("WillBeginImplFrame", client_);
+    EXPECT_TRUE(scheduler_->BeginImplFrameDeadlinePending());
+    EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+
+    client_->Reset();
+    scheduler_->DidSwapBuffersComplete();
+    scheduler_->NotifyBeginMainFrameStarted();
+    scheduler_->NotifyReadyToCommit();
+    scheduler_->NotifyReadyToActivate();
+    task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+
+    // Verify that we don't skip the actions of the BeginImplFrame
+    EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 0, 5);
+    EXPECT_ACTION("ScheduledActionCommit", client_, 1, 5);
+    EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 2, 5);
+    EXPECT_ACTION("ScheduledActionAnimate", client_, 3, 5);
+    EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 4, 5);
+  }
 }
 
-TEST_F(SchedulerTest, NotSkipMainFrameInPreferImplLatencyMode) {
-  // Set up client so that estimates indicate that we can commit and activate
-  // before the deadline (~8ms by default), but also enable impl latency takes
-  // priority mode.
-  EXPECT_SCOPED(MainFrameInHighLatencyMode(1, 1, true, true));
+TEST_F(SchedulerTest,
+       ImplFrameIsNotSkippedAfterLateSwapAck_CommitEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetBeginMainFrameToCommitDurationEstimate(
+      slow_duration);
+  EXPECT_SCOPED(ImplFrameIsNotSkippedAfterLateSwapAck());
+}
+
+TEST_F(SchedulerTest,
+       ImplFrameIsNotSkippedAfterLateSwapAck_ReadyToActivateEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetCommitToReadyToActivateDurationEstimate(
+      slow_duration);
+  EXPECT_SCOPED(ImplFrameIsNotSkippedAfterLateSwapAck());
+}
+
+TEST_F(SchedulerTest,
+       ImplFrameIsNotSkippedAfterLateSwapAck_ActivateEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetActivateDurationEstimate(slow_duration);
+  EXPECT_SCOPED(ImplFrameIsNotSkippedAfterLateSwapAck());
+}
+
+TEST_F(SchedulerTest,
+       ImplFrameIsNotSkippedAfterLateSwapAck_DrawEstimateTooLong) {
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetDrawDurationEstimate(slow_duration);
+  EXPECT_SCOPED(ImplFrameIsNotSkippedAfterLateSwapAck());
+}
+
+TEST_F(SchedulerTest,
+       MainFrameThenImplFrameSkippedAfterLateCommitAndLateSwapAck) {
+  // Set up client with custom estimates.
+  // This test starts off with expensive estimates to prevent latency recovery
+  // initially, then lowers the estimates to enable it once both the main
+  // and impl threads are in a high latency mode.
+  scheduler_settings_.use_external_begin_frame_source = true;
+  SetUpScheduler(true);
+
+  auto fast_duration = base::TimeDelta::FromMilliseconds(1);
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+  auto slow_duration = base::TimeDelta::FromSeconds(1);
+  fake_compositor_timing_history_->SetDrawDurationEstimate(slow_duration);

[sunnyps, 2015/07/08 22:37:13]

This doesn't match the comment above.

[brianderson, 2015/07/09 01:28:12]

Done.

+
+  // To get into a high latency state, this test disables automatic swap acks.
+  scheduler_->SetMaxSwapsPending(1);
+  client_->SetAutomaticSwapAck(false);
+
+  // Impl thread hits deadline before commit finishes to make
+  // MainThreadIsInHighLatencyMode true
+  client_->Reset();
+  scheduler_->SetNeedsCommit();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  EXPECT_SCOPED(AdvanceFrame());
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+  scheduler_->NotifyBeginMainFrameStarted();
+  scheduler_->NotifyReadyToCommit();
+  scheduler_->NotifyReadyToActivate();
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+
+  EXPECT_ACTION("SetNeedsBeginFrames(true)", client_, 0, 5);
+  EXPECT_ACTION("WillBeginImplFrame", client_, 1, 5);
+  EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 2, 5);
+  EXPECT_ACTION("ScheduledActionCommit", client_, 3, 5);
+  EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 4, 5);
+
+  // Draw and swap for first commit, start second commit.
+  client_->Reset();
+  scheduler_->SetNeedsCommit();
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+  EXPECT_SCOPED(AdvanceFrame());
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  scheduler_->NotifyBeginMainFrameStarted();
+  scheduler_->NotifyReadyToCommit();
+  scheduler_->NotifyReadyToActivate();
+
+  EXPECT_ACTION("WillBeginImplFrame", client_, 0, 6);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 1, 6);
+  EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 2, 6);
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 3, 6);
+  EXPECT_ACTION("ScheduledActionCommit", client_, 4, 6);
+  EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 5, 6);
+
+  // Don't call scheduler_->DidSwapBuffersComplete() until after next frame
+  // to put the impl thread in a high latency mode.
+  client_->Reset();
+  scheduler_->SetNeedsCommit();
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+  EXPECT_SCOPED(AdvanceFrame());
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  scheduler_->DidSwapBuffersComplete();
+
+  EXPECT_ACTION("WillBeginImplFrame", client_, 0, 2);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 1, 2);
+  // Note: BeginMainFrame and swap are skipped here because of
+  // swap ack backpressure, not because of latency recovery.
+  EXPECT_FALSE(client_->HasAction("ScheduledActionSendBeginMainFrame"));
+  EXPECT_FALSE(client_->HasAction("ScheduledActionDrawAndSwapIfPossible"));

[sunnyps, 2015/07/08 22:37:13]

EXPECT_TRUE that both impl thread and main thread are in high latency mode.

[brianderson, 2015/07/09 01:28:12]

Done.

+
+  // Lower estimates so that the scheduler will attempt latency recovery.
+  fake_compositor_timing_history_->SetAllEstimatesTo(fast_duration);
+
+  // Now that both threads are in a high latency mode, make sure we
+  // skip the BeginMainFrame, then the BeginImplFrame, but not both
+  // at the same time.
+
+  // Verify we skip BeginMainFrame first.
+  client_->Reset();
+  // Previous commit request is still outstanding.
+  EXPECT_TRUE(scheduler_->NeedsCommit());
+  EXPECT_TRUE(scheduler_->MainThreadIsInHighLatencyMode());
+  SendNextBeginFrame();

[sunnyps, 2015/07/08 22:37:13]

Same as above (before the deadline runs).

[brianderson, 2015/07/09 01:28:12]

Thanks for the suggestion. Found out I was calling DidSwapBuffersComplete on
line 1672 too early.

Had to make BeginImplFrameWithDeadline virtual for testing to make this work.

+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());

[sunnyps, 2015/07/08 22:37:13]

nit: Move this EXPECT below so that it reads sequentially.

[brianderson, 2015/07/09 01:28:11]

Done.

+
+  EXPECT_ACTION("WillBeginImplFrame", client_, 0, 3);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 1, 3);
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 2, 3);
+  EXPECT_FALSE(client_->HasAction("ScheduledActionSendBeginMainFrame"));

[sunnyps, 2015/07/08 22:37:13]

nit: Don't need the last EXPECT_FALSE.

[brianderson, 2015/07/09 01:28:11]

Done.

+
+  // Verify we skip the BeginImplFrame second.
+  client_->Reset();
+  // Previous commit request is still outstanding.
+  EXPECT_TRUE(scheduler_->NeedsCommit());
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  SendNextBeginFrame();
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  scheduler_->DidSwapBuffersComplete();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+
+  EXPECT_NO_ACTION(client_);
+
+  // Then verify we operate in a low latency mode.
+  client_->Reset();
+  // Previous commit request is still outstanding.
+  EXPECT_TRUE(scheduler_->NeedsCommit());
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  SendNextBeginFrame();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  scheduler_->NotifyBeginMainFrameStarted();
+  scheduler_->NotifyReadyToCommit();
+  scheduler_->NotifyReadyToActivate();
+  task_runner().RunTasksWhile(client_->ImplFrameDeadlinePending(true));
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+  scheduler_->DidSwapBuffersComplete();
+  EXPECT_FALSE(scheduler_->MainThreadIsInHighLatencyMode());
+
+  EXPECT_ACTION("WillBeginImplFrame", client_, 0, 6);
+  EXPECT_ACTION("ScheduledActionSendBeginMainFrame", client_, 1, 6);
+  EXPECT_ACTION("ScheduledActionCommit", client_, 2, 6);
+  EXPECT_ACTION("ScheduledActionActivateSyncTree", client_, 3, 6);
+  EXPECT_ACTION("ScheduledActionAnimate", client_, 4, 6);
+  EXPECT_ACTION("ScheduledActionDrawAndSwapIfPossible", client_, 5, 6);
 }
 
 TEST_F(