cc: Implement deadline scheduling disabled by default

This patch adds logic to the Scheduler to actually use the BeginFrame
and deadline, but is not enabled by default on any platform yet. This
will ensure emulation of old scheduler in the fallback path is sane.
Emulation of the old path is implemented using an immediate deadline.

SchedulerStateMachine::begin_frame_state has been added and can be in one
of 4 states: Idle, InsideBeginFrame, DeadlinePending, or InsideDeadline.

Notable restrictions of the states are:
- We start a commit as soon after InsideBeginFrame as we can, since the
BeginFrame will be coordinated with user input. (True on Android.
Soon to be true on other platforms.)
- We do not start a commit while Idle, in order to wait for the next
batch of user input.
- Draw and swap only occurs during the InsideDeadline state.

The deadlines of the Browser and Renderer compositors can be nested in
order to have a total draw latency of < 1 frame when starting off. If we
can't hit 1 frame of latency consistently, we will fall back to a higher
latency mode to increase throughput.

TBR=enne@chromium.org
BUG=243461

Review URL: https://chromiumcodereview.appspot.com/24070006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224560 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 136 insertions, 40 deletions

diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index c80d9cc..0d64d2d 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -14,22 +14,22 @@ namespace cc {
 SchedulerStateMachine::SchedulerStateMachine(const SchedulerSettings& settings)
     : settings_(settings),
       output_surface_state_(OUTPUT_SURFACE_LOST),
+      begin_frame_state_(BEGIN_FRAME_STATE_IDLE),
       commit_state_(COMMIT_STATE_IDLE),
       texture_state_(LAYER_TEXTURE_STATE_UNLOCKED),
       forced_redraw_state_(FORCED_REDRAW_STATE_IDLE),
       readback_state_(READBACK_STATE_IDLE),
       commit_count_(0),
       current_frame_number_(0),
-      last_frame_number_where_begin_frame_sent_to_main_thread_(-1),
       last_frame_number_swap_performed_(-1),
-      last_frame_number_where_update_visible_tiles_was_called_(-1),
+      last_frame_number_begin_frame_sent_to_main_thread_(-1),
+      last_frame_number_update_visible_tiles_was_called_(-1),
       consecutive_failed_draws_(0),
       needs_redraw_(false),
       needs_manage_tiles_(false),
       swap_used_incomplete_tile_(false),
       needs_commit_(false),
       main_thread_needs_layer_textures_(false),
-      inside_begin_frame_(false),
       inside_poll_for_anticipated_draw_triggers_(false),
       visible_(false),
       can_start_(false),
@@ -58,6 +58,22 @@ const char* SchedulerStateMachine::OutputSurfaceStateToString(
   return "???";
 }
 
+const char* SchedulerStateMachine::BeginFrameStateToString(
+    BeginFrameState state) {
+  switch (state) {
+    case BEGIN_FRAME_STATE_IDLE:
+      return "BEGIN_FRAME_STATE_IDLE";
+    case BEGIN_FRAME_STATE_BEGIN_FRAME_STARTING:
+      return "BEGIN_FRAME_STATE_BEGIN_FRAME_STARTING";
+    case BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME:
+      return "BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME";
+    case BEGIN_FRAME_STATE_INSIDE_DEADLINE:
+      return "BEGIN_FRAME_STATE_INSIDE_DEADLINE";
+  }
+  NOTREACHED();
+  return "???";
+}
+
 const char* SchedulerStateMachine::CommitStateToString(CommitState state) {
   switch (state) {
     case COMMIT_STATE_IDLE:
@@ -160,6 +176,8 @@ scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
 
   scoped_ptr<base::DictionaryValue> major_state(new base::DictionaryValue);
   major_state->SetString("next_action", ActionToString(NextAction()));
+  major_state->SetString("begin_frame_state",
+                         BeginFrameStateToString(begin_frame_state_));
   major_state->SetString("commit_state", CommitStateToString(commit_state_));
   major_state->SetString("texture_state_",
                          TextureStateToString(texture_state_));
@@ -202,14 +220,16 @@ scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
   scoped_ptr<base::DictionaryValue> minor_state(new base::DictionaryValue);
   minor_state->SetInteger("commit_count", commit_count_);
   minor_state->SetInteger("current_frame_number", current_frame_number_);
-  minor_state->SetInteger(
-      "last_frame_number_where_begin_frame_sent_to_main_thread",
-      last_frame_number_where_begin_frame_sent_to_main_thread_);
-  minor_state->SetInteger("last_frame_number_swap_performed_",
+
+  minor_state->SetInteger("last_frame_number_swap_performed",
                           last_frame_number_swap_performed_);
   minor_state->SetInteger(
-      "last_frame_number_where_update_visible_tiles_was_called",
-      last_frame_number_where_update_visible_tiles_was_called_);
+      "last_frame_number_begin_frame_sent_to_main_thread",
+      last_frame_number_begin_frame_sent_to_main_thread_);
+  minor_state->SetInteger(
+      "last_frame_number_update_visible_tiles_was_called",
+      last_frame_number_update_visible_tiles_was_called_);
+
   minor_state->SetInteger("consecutive_failed_draws",
                           consecutive_failed_draws_);
   minor_state->SetBoolean("needs_redraw", needs_redraw_);
@@ -219,14 +239,13 @@ scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
   minor_state->SetBoolean("needs_commit", needs_commit_);
   minor_state->SetBoolean("main_thread_needs_layer_textures",
                           main_thread_needs_layer_textures_);
-  minor_state->SetBoolean("inside_begin_frame", inside_begin_frame_);
   minor_state->SetBoolean("visible", visible_);
   minor_state->SetBoolean("can_start", can_start_);
   minor_state->SetBoolean("can_draw", can_draw_);
   minor_state->SetBoolean("has_pending_tree", has_pending_tree_);
-  minor_state->SetBoolean("pending_tree_is_ready_for_activation_",
+  minor_state->SetBoolean("pending_tree_is_ready_for_activation",
                           pending_tree_is_ready_for_activation_);
-  minor_state->SetBoolean("active_tree_needs_first_draw_",
+  minor_state->SetBoolean("active_tree_needs_first_draw",
                           active_tree_needs_first_draw_);
   minor_state->SetBoolean("draw_if_possible_failed", draw_if_possible_failed_);
   minor_state->SetBoolean("did_create_and_initialize_first_output_surface",
@@ -236,18 +255,18 @@ scoped_ptr<base::Value> SchedulerStateMachine::AsValue() const  {
   return state.PassAs<base::Value>();
 }
 
-bool SchedulerStateMachine::HasDrawnAndSwappedThisFrame() const {
-  return current_frame_number_ == last_frame_number_swap_performed_;
+bool SchedulerStateMachine::HasSentBeginFrameToMainThreadThisFrame() const {
+  return current_frame_number_ ==
+         last_frame_number_begin_frame_sent_to_main_thread_;
 }
 
 bool SchedulerStateMachine::HasUpdatedVisibleTilesThisFrame() const {
   return current_frame_number_ ==
-         last_frame_number_where_update_visible_tiles_was_called_;
+         last_frame_number_update_visible_tiles_was_called_;
 }
 
-bool SchedulerStateMachine::HasSentBeginFrameToMainThreadThisFrame() const {
-  return current_frame_number_ ==
-         last_frame_number_where_begin_frame_sent_to_main_thread_;
+bool SchedulerStateMachine::HasSwappedThisFrame() const {
+  return current_frame_number_ == last_frame_number_swap_performed_;
 }
 
 bool SchedulerStateMachine::PendingDrawsShouldBeAborted() const {
@@ -330,12 +349,12 @@ bool SchedulerStateMachine::ShouldDraw() const {
   if (PendingDrawsShouldBeAborted())
     return active_tree_needs_first_draw_;
 
-  // After this line, we only want to draw once per frame.
-  if (HasDrawnAndSwappedThisFrame())
+  // After this line, we only want to swap once per frame.
+  if (HasSwappedThisFrame())
     return false;
 
-  // We currently only draw within the BeginFrame.
-  if (!inside_begin_frame_)
+  // Except for the cases above, do not draw outside of the BeginFrame deadline.
+  if (begin_frame_state_ != BEGIN_FRAME_STATE_INSIDE_DEADLINE)
     return false;
 
   // Only handle forced redraws due to timeouts on the regular deadline.
@@ -385,10 +404,10 @@ bool SchedulerStateMachine::ShouldUpdateVisibleTiles() const {
   if (!HasInitializedOutputSurface())
     return false;
 
-  // We always want to update the most recent visible tiles before drawing
-  // so we draw with fewer missing tiles.
-  if (ShouldDraw())
-    return true;
+  // We should not check for visible tiles until we've entered the deadline so
+  // we check as late as possible and give the tiles more time to initialize.
+  if (begin_frame_state_ != BEGIN_FRAME_STATE_INSIDE_DEADLINE)
+    return false;
 
   // If the last swap drew with checkerboard or missing tiles, we should
   // poll for any new visible tiles so we can be notified to draw again
@@ -403,7 +422,8 @@ bool SchedulerStateMachine::ShouldSendBeginFrameToMainThread() const {
   if (!needs_commit_)
     return false;
 
-  // Only send BeginFrame to the main thread when idle.
+  // Only send BeginFrame to the main thread when there isn't another commit
+  // pending already.
   if (commit_state_ != COMMIT_STATE_IDLE)
     return false;
 
@@ -419,7 +439,7 @@ bool SchedulerStateMachine::ShouldSendBeginFrameToMainThread() const {
     return !CommitPending();
 
   // We do not need commits if we are not visible, unless there's a
-  // request for a forced commit.
+  // request for a readback.
   if (!visible_)
     return false;
 
@@ -427,6 +447,23 @@ bool SchedulerStateMachine::ShouldSendBeginFrameToMainThread() const {
   if (output_surface_state_ == OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT)
     return true;
 
+  // With deadline scheduling enabled, we should not send BeginFrame to the
+  // main thread while we are in BEGIN_FRAME_STATE_IDLE, since we might have
+  // new user input coming in soon.
+  // However, if we are not expecting a BeginFrame on the Impl thread to take
+  // us out of idle, we should not early out here to avoid blocking commits
+  // forever.
+  // This only works well when deadline scheduling is enabled because there is
+  // an interval over which to accept the commit and draw. Without deadline
+  // scheduling, delaying the commit could prevent us from having something
+  // to draw on the next BeginFrame.
+  // TODO(brianderson): Allow sending BeginFrame to main thread while idle
+  // when the main thread isn't consuming user input.
+  if (settings_.deadline_scheduling_enabled &&
+      begin_frame_state_ == BEGIN_FRAME_STATE_IDLE &&
+      BeginFrameNeededByImplThread())
+    return false;
+
   // We need a new commit for the forced redraw. This honors the
   // single commit per interval because the result will be swapped to screen.
   if (forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_COMMIT)
@@ -451,7 +488,8 @@ bool SchedulerStateMachine::ShouldManageTiles() const {
   // Limiting to once per-frame is not enough, since we only want to
   // manage tiles _after_ draws. Polling for draw triggers and
   // begin-frame are mutually exclusive, so we limit to these two cases.
-  if (!inside_begin_frame_ && !inside_poll_for_anticipated_draw_triggers_)
+  if (begin_frame_state_ != BEGIN_FRAME_STATE_INSIDE_DEADLINE &&
+      !inside_poll_for_anticipated_draw_triggers_)
     return false;
   return needs_manage_tiles_;
 }
@@ -497,7 +535,7 @@ void SchedulerStateMachine::UpdateState(Action action) {
       return;
 
     case ACTION_UPDATE_VISIBLE_TILES:
-      last_frame_number_where_update_visible_tiles_was_called_ =
+      last_frame_number_update_visible_tiles_was_called_ =
           current_frame_number_;
       return;
 
@@ -512,7 +550,7 @@ void SchedulerStateMachine::UpdateState(Action action) {
       needs_commit_ = false;
       if (readback_state_ == READBACK_STATE_NEEDS_BEGIN_FRAME)
         readback_state_ = READBACK_STATE_WAITING_FOR_COMMIT;
-      last_frame_number_where_begin_frame_sent_to_main_thread_ =
+      last_frame_number_begin_frame_sent_to_main_thread_ =
           current_frame_number_;
       return;
 
@@ -707,6 +745,33 @@ void SchedulerStateMachine::SetMainThreadNeedsLayerTextures() {
   main_thread_needs_layer_textures_ = true;
 }
 
+bool SchedulerStateMachine::BeginFrameNeededByImplThread() const {
+  // Proactive BeginFrames are bad for the synchronous compositor because we
+  // have to draw when we get the BeginFrame and could end up drawing many
+  // duplicate frames if our new frame isn't ready in time.
+  // To poll for state with the synchronous compositor without having to draw,
+  // we rely on ShouldPollForAnticipatedDrawTriggers instead.
+  if (settings_.using_synchronous_renderer_compositor)
+    return BeginFrameNeededToDrawByImplThread();
+
+  return BeginFrameNeededToDrawByImplThread() ||
+         ProactiveBeginFrameWantedByImplThread();
+}
+
+bool SchedulerStateMachine::ShouldPollForAnticipatedDrawTriggers() const {
+  // ShouldPollForAnticipatedDrawTriggers is what we use in place of
+  // ProactiveBeginFrameWantedByImplThread when we are using the synchronous
+  // compositor.
+  if (settings_.using_synchronous_renderer_compositor) {
+    return !BeginFrameNeededToDrawByImplThread() &&
+           ProactiveBeginFrameWantedByImplThread();
+  }
+
+  // Non synchronous compositors should rely on
+  // ProactiveBeginFrameWantedByImplThread to poll for state instead.
+  return false;
+}
+
 // These are the cases where we definitely (or almost definitely) have a
 // new frame to draw and can draw.
 bool SchedulerStateMachine::BeginFrameNeededToDrawByImplThread() const {
@@ -741,15 +806,16 @@ bool SchedulerStateMachine::BeginFrameNeededToDrawByImplThread() const {
 // actually have a new frame to draw when we receive the next BeginFrame.
 // Proactively requesting the BeginFrame helps hide the round trip latency of
 // the SetNeedsBeginFrame request that has to go to the Browser.
-// However, this is bad for the synchronous compositor because we have to
-// draw when we get the BeginFrame and could end up drawing many duplicate
-// frames.
 bool SchedulerStateMachine::ProactiveBeginFrameWantedByImplThread() const {
   // The output surface is the provider of BeginFrames for the impl thread,
   // so we are not going to get them even if we ask for them.
   if (!HasInitializedOutputSurface())
     return false;
 
+  // Do not be proactive if vsync is off.
+  if (!settings_.throttle_frame_production)
+    return false;
+
   // Do not be proactive when invisible.
   if (!visible_)
     return false;
@@ -779,14 +845,43 @@ bool SchedulerStateMachine::ProactiveBeginFrameWantedByImplThread() const {
   return false;
 }
 
-void SchedulerStateMachine::DidEnterBeginFrame(const BeginFrameArgs& args) {
+void SchedulerStateMachine::OnBeginFrame(const BeginFrameArgs& args) {
   current_frame_number_++;
-  inside_begin_frame_ = true;
   last_begin_frame_args_ = args;
+  DCHECK_EQ(begin_frame_state_, BEGIN_FRAME_STATE_IDLE)
+    << *AsValue();
+  begin_frame_state_ = BEGIN_FRAME_STATE_BEGIN_FRAME_STARTING;
 }
 
-void SchedulerStateMachine::DidLeaveBeginFrame() {
-  inside_begin_frame_ = false;
+void SchedulerStateMachine::OnBeginFrameDeadlinePending() {
+  DCHECK_EQ(begin_frame_state_, BEGIN_FRAME_STATE_BEGIN_FRAME_STARTING)
+      << *AsValue();
+  begin_frame_state_ = BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME;
+}
+
+void SchedulerStateMachine::OnBeginFrameDeadline() {
+  DCHECK_EQ(begin_frame_state_, BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME)
+    << *AsValue();
+  begin_frame_state_ = BEGIN_FRAME_STATE_INSIDE_DEADLINE;
+}
+
+void SchedulerStateMachine::OnBeginFrameIdle() {
+  if (HasInitializedOutputSurface()) {
+    DCHECK_EQ(begin_frame_state_, BEGIN_FRAME_STATE_INSIDE_DEADLINE)
+        << *AsValue();
+  }
+  begin_frame_state_ = BEGIN_FRAME_STATE_IDLE;
+}
+
+bool SchedulerStateMachine::ShouldTriggerBeginFrameDeadlineEarly() const {
+  // If we are in the middle of the readback, we won't swap, so there is
+  // no reason to trigger the deadline early.
+  if (readback_state_ != READBACK_STATE_IDLE)
+    return false;
+
+  // TODO(brianderson): This should take into account multiple commit sources.
+  return begin_frame_state_ == BEGIN_FRAME_STATE_INSIDE_BEGIN_FRAME &&
+         active_tree_needs_first_draw_;
 }
 
 void SchedulerStateMachine::DidEnterPollForAnticipatedDrawTriggers() {
@@ -800,6 +895,8 @@ void SchedulerStateMachine::DidLeavePollForAnticipatedDrawTriggers() {
 
 void SchedulerStateMachine::SetVisible(bool visible) { visible_ = visible; }
 
+void SchedulerStateMachine::SetCanDraw(bool can_draw) { can_draw_ = can_draw; }
+
 void SchedulerStateMachine::SetNeedsRedraw() { needs_redraw_ = true; }
 
 void SchedulerStateMachine::SetNeedsManageTiles() {
@@ -876,6 +973,7 @@ void SchedulerStateMachine::DidLoseOutputSurface() {
     return;
   output_surface_state_ = OUTPUT_SURFACE_LOST;
   needs_redraw_ = false;
+  begin_frame_state_ = BEGIN_FRAME_STATE_IDLE;
 }
 
 void SchedulerStateMachine::NotifyReadyToActivate() {
@@ -883,8 +981,6 @@ void SchedulerStateMachine::NotifyReadyToActivate() {
     pending_tree_is_ready_for_activation_ = true;
 }
 
-void SchedulerStateMachine::SetCanDraw(bool can) { can_draw_ = can; }
-
 void SchedulerStateMachine::DidCreateAndInitializeOutputSurface() {
   DCHECK_EQ(output_surface_state_, OUTPUT_SURFACE_CREATING);
   output_surface_state_ = OUTPUT_SURFACE_WAITING_FOR_FIRST_COMMIT;