Optimize for TouchStart responsiveness

components/scheduler/renderer/renderer_scheduler_impl.h

 // Copyright 2014 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.
 
 #ifndef COMPONENTS_SCHEDULER_RENDERER_RENDERER_SCHEDULER_IMPL_H_
 #define COMPONENTS_SCHEDULER_RENDERER_RENDERER_SCHEDULER_IMPL_H_
 
 #include "base/atomicops.h"
 #include "base/synchronization/lock.h"
 #include "components/scheduler/child/idle_helper.h"
@@ skipping 47 matching lines @@
   void SuspendTimerQueue() override;
   void ResumeTimerQueue() override;
 
   SchedulerHelper* GetSchedulerHelperForTesting();
   base::TimeTicks CurrentIdleTaskDeadlineForTesting() const;
 
  private:
   friend class RendererSchedulerImplTest;
   friend class RendererSchedulerImplForTest;
 
-  // Keep RendererSchedulerImpl::PolicyToString in sync with this enum.
-  enum class Policy {
-    NORMAL,
-    COMPOSITOR_PRIORITY,
-    COMPOSITOR_CRITICAL_PATH_PRIORITY,
-    TOUCHSTART_PRIORITY,
-    LOADING_PRIORITY,
+  // Keep RendererSchedulerImpl::UseCaseToString in sync with this enum.
+  enum class UseCase {
+    NOT_SCROLLING,

[Sami, 2015/08/26 13:38:02]

I feel like scrolling as a term is too narrow since there are also things like
pinch-to-zoom that fall under this. How about COMPOSITOR_INTERACTION vs.
MAIN_THREAD_INTERACTION or something? Also, the base case could just be IDLE?

[alex clarke (OOO till 29th), 2015/08/27 12:02:51]

As discussed offline I went with COMPOSITOR_GESTURE & MAIN_THREAD_GESTURE

+    COMPOSITOR_SCROLLING,
+    MAINTHREAD_SCROLLING,

[Sami, 2015/08/26 13:38:02]

nit: MAIN_THREAD_SCROLLING

[alex clarke (OOO till 29th), 2015/08/27 12:02:51]

Acknowledged.

+    TOUCHSTART,
+    LOADING,
     // Must be the last entry.
-    POLICY_COUNT,
-    FIRST_POLICY = NORMAL,
+    USE_CASE_COUNT,
+    FIRST_USE_CASE = NOT_SCROLLING,
+  };
+
+  struct Policy {
+    Policy();
+
+    TaskQueue::QueuePriority compositor_queue_priority_;

[Sami, 2015/08/26 13:38:02]

Public struct members shouldn't have trailing underscores (yep, we've got other
places where we're doing this wrong atm.)

[alex clarke (OOO till 29th), 2015/08/27 12:02:51]

OK lets fix em.  Or at least the ones in this class.

+    TaskQueue::QueuePriority loading_queue_priority_;
+    TaskQueue::QueuePriority timer_queue_priority_;
+
+    bool operator==(const Policy& other) const {
+      return compositor_queue_priority_ == other.compositor_queue_priority_ &&
+             loading_queue_priority_ == other.loading_queue_priority_ &&
+             timer_queue_priority_ == other.timer_queue_priority_;
+    }
   };
 
   class PollableNeedsUpdateFlag {
    public:
     PollableNeedsUpdateFlag(base::Lock* write_lock);
     ~PollableNeedsUpdateFlag();
 
     // Set the flag. May only be called if |write_lock| is held.
     void SetWhileLocked(bool value);
 
@@ skipping 15 matching lines @@
   void OnIdlePeriodStarted() override;
   void OnIdlePeriodEnded() override;
 
   void EndIdlePeriod();
 
   // Returns the serialized scheduler state for tracing.
   scoped_refptr<base::trace_event::ConvertableToTraceFormat> AsValue(
       base::TimeTicks optional_now) const;
   scoped_refptr<base::trace_event::ConvertableToTraceFormat> AsValueLocked(
       base::TimeTicks optional_now) const;
-  static const char* PolicyToString(Policy policy);
+  static const char* UseCaseToString(UseCase use_case);
 
   static bool ShouldPrioritizeInputEvent(
       const blink::WebInputEvent& web_input_event);
 
   // The time we should stay in a priority-escalated mode after an input event.
   static const int kPriorityEscalationAfterInputMillis = 100;
 
+  // We consider further input invents to be likely if the user has interacted
+  // with the device in the past two seconds.
+  // TODO(alexclarke): Get a real number based on actual data.
+  static const int kExpectSubsequentInputMillis = 2000;
+
   // The amount of time which idle periods can continue being scheduled when the
   // renderer has been hidden, before going to sleep for good.
   static const int kEndIdleWhenHiddenDelayMillis = 10000;
 
   // The amount of time for which loading tasks will be prioritized over
   // other tasks during the initial page load.
   static const int kRailsInitialLoadingPrioritizationMillis = 1000;
 
+  // TODO(alexclarke): Get a real number on actual data.
+  static const int kMinimumTypicalScrollDurationMillis = 500;
+
   // For the purposes of deciding whether or not it's safe to turn timers and
   // loading tasks on only in idle periods, we regard the system as being as
   // being "idle period" starved if there hasn't been an idle period in the last
   // 10 seconds. This was chosen to be long enough to cover most anticipated
   // user gestures.
   static const int kIdlePeriodStarvationThresholdMillis = 10000;
 
   // Schedules an immediate PolicyUpdate, if there isn't one already pending and
   // sets |policy_may_need_update_|. Note |any_thread_lock_| must be
   // locked.
@@ skipping 17 matching lines @@
   };
 
   // The implelemtation of UpdatePolicy & ForceUpdatePolicy.  It is allowed to
   // early out if |update_type| is MAY_EARLY_OUT_IF_POLICY_UNCHANGED.
   virtual void UpdatePolicyLocked(UpdateType update_type);
 
   // Returns the amount of time left in the current input escalated priority
   // policy.  Can be called from any thread.
   base::TimeDelta TimeLeftInInputEscalatedPolicy(base::TimeTicks now) const;
 
-  // Helper for computing the new policy. |new_policy_duration| will be filled
+  // Helper for computing the policy. |new_policy_duration| will be filled
   // with the amount of time after which the policy should be updated again. If
   // the duration is zero, a new policy update will not be scheduled. Must be
   // called with |any_thread_lock_| held. Can be called from any thread.
-  Policy ComputeNewPolicy(base::TimeTicks now,
-                          base::TimeDelta* new_policy_duration) const;
+  UseCase ComputeCurrentUseCase(base::TimeTicks now,
+                                base::TimeDelta* new_policy_duration) const;

[Sami, 2015/08/26 13:38:02]

Should this now be the policy duration or the use case duration?

[alex clarke (OOO till 29th), 2015/08/27 12:02:51]

How about expected_use_case_duration?

 
   // Works out if compositor tasks would be prioritized based on the current
   // input signals.  Can be called from any thread.
-  bool InputSignalsSuggestCompositorPriority(base::TimeTicks now) const;
+  bool InputSignalsSuggestScrolling(base::TimeTicks now) const;

[Sami, 2015/08/26 13:38:02]

Suggest main thread scrolling?

[alex clarke (OOO till 29th), 2015/08/27 12:02:51]

This is used to avoid posting lots of policy updates from the compositor thread.
 As discussed offline I think InputSignalsSuggestGestureInProgress is a better
name.

 
   // An input event of some sort happened, the policy may need updating.
   void UpdateForInputEventOnCompositorThread(blink::WebInputEvent::Type type,
                                              InputEventState input_event_state);
 
   // Returns true if there has been at least one idle period in the last
   // |kIdlePeriodStarvationThresholdMillis|.
   bool HadAnIdlePeriodRecently(base::TimeTicks now) const;
 
+  // Tries to guess if the user is likely to happen soon. Currently this is
+  // very simple, but one day I hope to do something more sophisticated here.
+  bool ScrollExpectedSoon(UseCase use_case,

[Sami, 2015/08/26 13:38:02]

Could you split all the logic about predicting the user into a new UserModel
class? I suspect it's going to become a lot more complicated and it's fairly
independent anyway.

[alex clarke (OOO till 29th), 2015/08/27 12:02:51]

Done.

+                          const base::TimeTicks now,
+                          base::TimeDelta* new_policy_duration) const;
+
   SchedulerHelper helper_;
   IdleHelper idle_helper_;
 
   const scoped_refptr<TaskQueue> control_task_runner_;
   const scoped_refptr<TaskQueue> compositor_task_runner_;
   const scoped_refptr<TaskQueue> loading_task_runner_;
   const scoped_refptr<TaskQueue> timer_task_runner_;
 
   base::Closure update_policy_closure_;
   DeadlineTaskRunner delayed_update_policy_runner_;
   CancelableClosureHolder end_renderer_hidden_idle_period_closure_;
 
   // We have decided to improve thread safety at the cost of some boilerplate
   // (the accessors) for the following data members.
 
   struct MainThreadOnly {
     MainThreadOnly();
     ~MainThreadOnly();
 
+    TaskCostEstimator loading_task_cost_estimator_;
     TaskCostEstimator timer_task_cost_estimator_;
     cc::RollingTimeDeltaHistory short_idle_period_duration_;
+    UseCase current_use_case_;
     Policy current_policy_;
     base::TimeTicks current_policy_expiration_time_;
     base::TimeTicks estimated_next_frame_begin_;
     base::TimeDelta expected_short_idle_period_duration_;
     int timer_queue_suspend_count_;  // TIMER_TASK_QUEUE suspended if non-zero.
     bool renderer_hidden_;
     bool was_shutdown_;
+    bool loading_tasks_seem_expensive_;
+    bool timer_tasks_seem_expensive_;
+    bool scroll_expected_soon_;
   };
 
   struct AnyThread {
     AnyThread();
 
     base::TimeTicks last_input_signal_time_;
     base::TimeTicks last_idle_period_end_time_;
     base::TimeTicks rails_loading_priority_deadline_;
+    base::TimeTicks last_touchstart_time_;
     int pending_main_thread_input_event_count_;
     bool awaiting_touch_start_response_;
     bool in_idle_period_;
     bool begin_main_frame_on_critical_path_;
-    bool timer_tasks_seem_expensive_;
   };
 
   struct CompositorThreadOnly {
     CompositorThreadOnly();
     ~CompositorThreadOnly();
 
     blink::WebInputEvent::Type last_input_type_;
     scoped_ptr<base::ThreadChecker> compositor_thread_checker_;
 
     void CheckOnValidThread() {
@@ skipping 39 matching lines @@
 
   PollableThreadSafeFlag policy_may_need_update_;
   base::WeakPtrFactory<RendererSchedulerImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RendererSchedulerImpl);
 };
 
 }  // namespace scheduler
 
 #endif  // COMPONENTS_SCHEDULER_RENDERER_RENDERER_SCHEDULER_IMPL_H_