[scheduler] Implement time-based cpu throttling.

third_party/WebKit/Source/platform/scheduler/renderer/task_queue_throttler.cc

Index: third_party/WebKit/Source/platform/scheduler/renderer/task_queue_throttler.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/renderer/task_queue_throttler.cc b/third_party/WebKit/Source/platform/scheduler/renderer/task_queue_throttler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a42374af9a24b44a539af66c1a0ba104e156a7e9
--- /dev/null
+++ b/third_party/WebKit/Source/platform/scheduler/renderer/task_queue_throttler.cc
@@ -0,0 +1,590 @@
+// Copyright 2015 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 "platform/scheduler/renderer/task_queue_throttler.h"
+
+#include <cstdint>
+
+#include "base/format_macros.h"
+#include "base/logging.h"
+#include "base/memory/ptr_util.h"
+#include "base/optional.h"
+#include "base/strings/stringprintf.h"
+#include "platform/scheduler/base/real_time_domain.h"
+#include "platform/scheduler/child/scheduler_tqm_delegate.h"
+#include "platform/scheduler/renderer/auto_advancing_virtual_time_domain.h"
+#include "platform/scheduler/renderer/renderer_scheduler_impl.h"
+#include "platform/scheduler/renderer/throttled_time_domain.h"
+#include "platform/scheduler/renderer/web_frame_scheduler_impl.h"
+#include "public/platform/WebFrameScheduler.h"
+
+namespace blink {
+namespace scheduler {
+
+namespace {
+const int kMaxBudgetLevelInSeconds = 1;
+
+base::Optional<base::TimeTicks> NextTaskRunTime(LazyNow* lazy_now,
+                                                TaskQueue* queue) {
+  if (queue->HasPendingImmediateWork())
+    return lazy_now->Now();
+  return queue->GetNextScheduledWakeUp();
+}
+}
+
+TaskQueueThrottler::TimeBudgetPool::TimeBudgetPool(
+    const char* name,
+    TaskQueueThrottler* task_queue_throttler,
+    base::TimeTicks now)
+    : name_(name),
+      task_queue_throttler_(task_queue_throttler),
+      max_budget_level_(base::TimeDelta::FromSeconds(kMaxBudgetLevelInSeconds)),
+      last_checkpoint_(now),
+      cpu_percentage_(1),
+      is_enabled_(true) {}
+
+TaskQueueThrottler::TimeBudgetPool::~TimeBudgetPool() {}
+
+void TaskQueueThrottler::TimeBudgetPool::SetTimeBudget(base::TimeTicks now,
+                                                       double cpu_percentage) {
+  Advance(now);
+  cpu_percentage_ = cpu_percentage;
+}
+
+void TaskQueueThrottler::TimeBudgetPool::AddQueue(base::TimeTicks now,
+                                                  TaskQueue* queue) {
+  Metadata& metadata = task_queue_throttler_->queue_details_[queue];
+  DCHECK(!metadata.time_budget_pool);
+  metadata.time_budget_pool = this;
+
+  associated_task_queues_.insert(queue);
+
+  if (metadata->throttling_ref_count == 0)

[alex clarke (OOO till 29th), 2016/09/16 15:23:38]

Lets add an IsThrottled() helper function.

[altimin, 2016/09/16 16:32:25]

Done.

+    return;
+
+  queue->SetQueueEnabled(false);
+
+  task_queue_throttler_->MaybeSchedulePumpQueue(FROM_HERE, now, queue,
+                                                GetNextAllowedRunTime());
+}
+
+void TaskQueueThrottler::TimeBudgetPool::RemoveQueue(base::TimeTicks now,
+                                                     TaskQueue* queue) {
+  auto find_it = task_queue_throttler_->queue_details_.find(queue);
+  DCHECK(find_it != task_queue_throttler_->queue_details_.end() &&
+         find_it->second.time_budget_pool == this);
+  find_it->second.time_budget_pool = nullptr;
+  bool is_throttled = find_it->second.throttling_ref_count > 0;
+
+  task_queue_throttler_->MaybeDeleteQueueMetadata(find_it);
+  associated_task_queues_.erase(queue);
+
+  if (is_throttled)
+    return;
+
+  task_queue_throttler_->MaybeSchedulePumpQueue(FROM_HERE, now, queue,
+                                                base::nullopt);
+}
+
+void TaskQueueThrottler::TimeBudgetPool::EnableThrottling(LazyNow* lazy_now) {
+  if (is_enabled_)
+    return;
+  is_enabled_ = true;
+
+  for (TaskQueue* queue : associated_task_queues_) {
+    if (!task_queue_throttler_->IsThrottled(queue))
+      continue;
+
+    queue->SetQueueEnabled(false);
+
+    task_queue_throttler_->MaybeSchedulePumpQueue(
+        FROM_HERE, lazy_now->Now(), queue, GetNextAllowedRunTime());
+  }
+}
+
+void TaskQueueThrottler::TimeBudgetPool::DisableThrottling(LazyNow* lazy_now) {
+  if (!is_enabled_)
+    return;
+  is_enabled_ = false;
+
+  for (TaskQueue* queue : associated_task_queues_) {
+    if (!task_queue_throttler_->IsThrottled(queue))
+      continue;
+
+    task_queue_throttler_->MaybeSchedulePumpQueue(FROM_HERE, lazy_now->Now(),
+                                                  queue, base::nullopt);
+  }
+}
+
+bool TaskQueueThrottler::TimeBudgetPool::IsThrottlingEnabled() const {
+  return is_enabled_;
+}
+
+void TaskQueueThrottler::TimeBudgetPool::Close() {
+  DCHECK_EQ(0u, associated_task_queues_.size());
+
+  task_queue_throttler_->time_budget_pools_.erase(this);
+}
+
+bool TaskQueueThrottler::TimeBudgetPool::HasEnoughBudgetToRun(
+    base::TimeTicks now) {
+  Advance(now);
+  return !is_enabled_ || current_budget_level_.InMicroseconds() >= 0;
+}
+
+base::TimeTicks TaskQueueThrottler::TimeBudgetPool::GetNextAllowedRunTime() {
+  if (!is_enabled_ || current_budget_level_.InMicroseconds() >= 0) {
+    return last_checkpoint_;
+  } else {
+    // Subtract because current_budget is negative.
+    return last_checkpoint_ - current_budget_level_ / cpu_percentage_;
+  }
+}
+
+void TaskQueueThrottler::TimeBudgetPool::RecordTaskRunTime(
+    base::TimeDelta task_run_time) {
+  if (is_enabled_) {
+    current_budget_level_ -= task_run_time;
+  }
+}
+
+const char* TaskQueueThrottler::TimeBudgetPool::Name() const {
+  return name_;
+}
+
+void TaskQueueThrottler::TimeBudgetPool::AsValueInto(
+    base::trace_event::TracedValue* state,
+    base::TimeTicks now) const {
+  state->BeginDictionary();
+
+  state->SetString("name", name_);
+  state->SetDouble("time_budget", cpu_percentage_);
+  state->SetDouble("time_budget_level_in_seconds",
+                   current_budget_level_.InSecondsF());
+  state->SetDouble("last_checkpoint_seconds_ago",
+                   (now - last_checkpoint_).InSecondsF());
+
+  state->BeginArray("task_queues");
+  for (TaskQueue* queue : associated_task_queues_) {
+    state->AppendString(base::StringPrintf(
+        "%" PRIx64, static_cast<uint64_t>(reinterpret_cast<uintptr_t>(queue))));
+  }
+  state->EndArray();
+
+  state->EndDictionary();
+}
+
+void TaskQueueThrottler::TimeBudgetPool::Advance(base::TimeTicks now) {
+  if (now > last_checkpoint_) {
+    if (is_enabled_) {
+      current_budget_level_ = std::min(
+          current_budget_level_ + cpu_percentage_ * (now - last_checkpoint_),
+          max_budget_level_);
+    }
+    last_checkpoint_ = now;
+  }
+}
+
+void TaskQueueThrottler::TimeBudgetPool::BlockQueues(base::TimeTicks now) {
+  for (TaskQueue* queue : associated_task_queues_) {
+    if (!task_queue_throttler_->IsThrottled(queue))
+      continue;
+
+    queue->SetQueueEnabled(false);
+    task_queue_throttler_->MaybeSchedulePumpQueue(FROM_HERE, now, queue,
+                                                  base::nullopt);
+  }
+}
+
+TaskQueueThrottler::TaskQueueThrottler(
+    RendererSchedulerImpl* renderer_scheduler,
+    const char* tracing_category)
+    : task_runner_(renderer_scheduler->ControlTaskRunner()),
+      renderer_scheduler_(renderer_scheduler),
+      tick_clock_(renderer_scheduler->tick_clock()),
+      tracing_category_(tracing_category),
+      time_domain_(new ThrottledTimeDomain(this, tracing_category)),
+      virtual_time_(false),
+      weak_factory_(this) {
+  pump_throttled_tasks_closure_.Reset(base::Bind(
+      &TaskQueueThrottler::PumpThrottledTasks, weak_factory_.GetWeakPtr()));
+  forward_immediate_work_callback_ =
+      base::Bind(&TaskQueueThrottler::OnTimeDomainHasImmediateWork,
+                 weak_factory_.GetWeakPtr());
+
+  renderer_scheduler_->RegisterTimeDomain(time_domain_.get());
+}
+
+TaskQueueThrottler::~TaskQueueThrottler() {
+  // It's possible for queues to be still throttled, so we need to tidy up
+  // before unregistering the time domain.
+  for (const TaskQueueMap::value_type& map_entry : queue_details_) {
+    if (map_entry.second.throttling_ref_count > 0) {
+      TaskQueue* task_queue = map_entry.first;
+      task_queue->SetTimeDomain(renderer_scheduler_->real_time_domain());
+      task_queue->RemoveFence();
+    }
+  }
+
+  renderer_scheduler_->UnregisterTimeDomain(time_domain_.get());
+}
+
+void TaskQueueThrottler::SetQueueEnabled(TaskQueue* task_queue, bool enabled) {
+  TaskQueueMap::iterator find_it = queue_details_.find(task_queue);
+
+  if (find_it == queue_details_.end()) {
+    task_queue->SetQueueEnabled(enabled);
+    return;
+  }
+
+  find_it->second.enabled = enabled;
+
+  if (find_it->second.throttling_ref_count == 0)
+    return;
+
+  // We don't enable the queue here because it's throttled and there might be
+  // tasks in it's work queue that would execute immediatly rather than after
+  // PumpThrottledTasks runs.
+  if (!enabled) {
+    task_queue->SetQueueEnabled(false);
+    MaybeSchedulePumpQueue(FROM_HERE, tick_clock_->NowTicks(), task_queue,
+                           base::nullopt);
+  }
+}
+
+void TaskQueueThrottler::IncreaseThrottleRefCount(TaskQueue* task_queue) {
+  DCHECK_NE(task_queue, task_runner_.get());
+
+  if (virtual_time_)
+    return;
+
+  std::pair<TaskQueueMap::iterator, bool> insert_result =
+      queue_details_.insert(std::make_pair(task_queue, Metadata()));
+
+  if (insert_result.first->second.throttling_ref_count == 0) {
+    // The insert was successful so we need to throttle the queue.
+    insert_result.first->second.enabled = task_queue->IsQueueEnabled();
+
+    task_queue->SetTimeDomain(time_domain_.get());
+    task_queue->RemoveFence();
+    task_queue->SetQueueEnabled(false);
+
+    if (!task_queue->IsEmpty()) {
+      if (task_queue->HasPendingImmediateWork()) {
+        OnTimeDomainHasImmediateWork(task_queue);
+      } else {
+        OnTimeDomainHasDelayedWork(task_queue);
+      }
+    }
+
+    TRACE_EVENT1(tracing_category_, "TaskQueueThrottler_TaskQueueThrottled",
+                 "task_queue", task_queue);
+  }
+
+  insert_result.first->second.throttling_ref_count++;
+}
+
+void TaskQueueThrottler::DecreaseThrottleRefCount(TaskQueue* task_queue) {
+  if (virtual_time_)
+    return;
+
+  TaskQueueMap::iterator iter = queue_details_.find(task_queue);
+
+  if (iter != queue_details_.end() &&
+      --iter->second.throttling_ref_count == 0) {
+    bool enabled = iter->second.enabled;
+
+    MaybeDeleteQueueMetadata(iter);
+
+    task_queue->SetTimeDomain(renderer_scheduler_->real_time_domain());
+    task_queue->RemoveFence();
+    task_queue->SetQueueEnabled(enabled);
+
+    TRACE_EVENT1(tracing_category_, "TaskQueueThrottler_TaskQueueUntrottled",
+                 "task_queue", task_queue);
+  }
+}
+
+bool TaskQueueThrottler::IsThrottled(TaskQueue* task_queue) const {
+  auto find_it = queue_details_.find(task_queue);
+  if (find_it == queue_details_.end())
+    return false;
+  return find_it->second.throttling_ref_count > 0;
+}
+
+void TaskQueueThrottler::UnregisterTaskQueue(TaskQueue* task_queue) {
+  LazyNow lazy_now(tick_clock_);
+  auto find_it = queue_details_.find(task_queue);
+
+  if (find_it == queue_details_.end())
+    return;
+
+  if (find_it->second.time_budget_pool)
+    find_it->second.time_budget_pool->RemoveQueue(lazy_now.Now(), task_queue);
+
+  queue_details_.erase(find_it);
+}
+
+void TaskQueueThrottler::OnTimeDomainHasImmediateWork(TaskQueue* queue) {
+  // Forward to the main thread if called from another thread
+  if (!task_runner_->RunsTasksOnCurrentThread()) {
+    task_runner_->PostTask(FROM_HERE,
+                           base::Bind(forward_immediate_work_callback_, queue));
+    return;
+  }
+  TRACE_EVENT0(tracing_category_,
+               "TaskQueueThrottler::OnTimeDomainHasImmediateWork");
+
+  base::TimeTicks now = tick_clock_->NowTicks();
+  base::TimeTicks next_allowed_run_time = GetNextAllowedRunTime(now, queue);
+  MaybeSchedulePumpThrottledTasks(FROM_HERE, now, next_allowed_run_time);
+}
+
+void TaskQueueThrottler::OnTimeDomainHasDelayedWork(TaskQueue* queue) {
+  TRACE_EVENT0(tracing_category_,
+               "TaskQueueThrottler::OnTimeDomainHasDelayedWork");
+  base::TimeTicks now = tick_clock_->NowTicks();
+  LazyNow lazy_now(now);
+
+  base::Optional<base::TimeTicks> next_scheduled_delayed_task =
+      NextTaskRunTime(&lazy_now, queue);
+  DCHECK(next_scheduled_delayed_task);
+  MaybeSchedulePumpThrottledTasks(FROM_HERE, now,
+                                  next_scheduled_delayed_task.value());
+}
+
+namespace {
+
+template <class T>
+T Min(const base::Optional<T>& optional, const T& value) {
+  if (!optional) {
+    return value;
+  }
+  return std::min(optional.value(), value);
+}
+
+template <class T>
+base::Optional<T> Min(const base::Optional<T>& a, const base::Optional<T>& b) {
+  if (!b)
+    return a;
+  if (!a)
+    return b;
+  return std::min(a.value(), b.value());
+}
+
+template <class T>
+T Max(const base::Optional<T>& optional, const T& value) {
+  if (!optional)
+    return value;
+  return std::max(optional.value(), value);
+}
+
+template <class T>
+base::Optional<T> Max(const base::Optional<T>& a, const base::Optional<T>& b) {
+  if (!b)
+    return a;
+  if (!a)
+    return b;
+  return std::max(a.value(), b.value());
+}
+
+}  // namespace
+
+void TaskQueueThrottler::PumpThrottledTasks() {
+  TRACE_EVENT0(tracing_category_, "TaskQueueThrottler::PumpThrottledTasks");
+  pending_pump_throttled_tasks_runtime_.reset();
+
+  LazyNow lazy_now(tick_clock_);
+  base::Optional<base::TimeTicks> next_scheduled_delayed_task;
+
+  for (const TaskQueueMap::value_type& map_entry : queue_details_) {
+    TaskQueue* task_queue = map_entry.first;
+    if (!map_entry.second.enabled || task_queue->IsEmpty() ||
+        map_entry.second.throttling_ref_count == 0)
+      continue;
+
+    // Don't enable queues whose budget pool doesn't allow them to run now.
+    base::TimeTicks next_allowed_run_time =
+        GetNextAllowedRunTime(lazy_now.Now(), task_queue);
+    base::Optional<base::TimeTicks> next_desired_run_time =
+        NextTaskRunTime(&lazy_now, task_queue);
+
+    if (next_desired_run_time &&
+        next_allowed_run_time > next_desired_run_time.value()) {
+      TRACE_EVENT1(
+          tracing_category_,
+          "TaskQueueThrottler::PumpThrottledTasks_ExpensiveTaskThrottled",
+          "throttle_time_in_seconds",
+          (next_allowed_run_time - next_desired_run_time.value()).InSecondsF());
+
+      // Schedule a pump for queue which was disabled because of time budget.
+      next_scheduled_delayed_task =
+          Min(next_scheduled_delayed_task, next_allowed_run_time);
+
+      continue;
+    }
+
+    next_scheduled_delayed_task =
+        Min(next_scheduled_delayed_task, task_queue->GetNextScheduledWakeUp());
+
+    if (next_allowed_run_time > lazy_now.Now())
+      continue;
+
+    task_queue->SetQueueEnabled(true);
+    task_queue->InsertFence();
+  }
+
+  // Maybe schedule a call to TaskQueueThrottler::PumpThrottledTasks if there is
+  // a pending delayed task or a throttled task ready to run.
+  // NOTE: posting a non-delayed task in the future will result in
+  // TaskQueueThrottler::OnTimeDomainHasImmediateWork being called.
+  if (next_scheduled_delayed_task) {
+    MaybeSchedulePumpThrottledTasks(FROM_HERE, lazy_now.Now(),
+                                    *next_scheduled_delayed_task);
+  }
+}
+
+/* static */
+base::TimeTicks TaskQueueThrottler::AlignedThrottledRunTime(
+    base::TimeTicks unthrottled_runtime) {
+  const base::TimeDelta one_second = base::TimeDelta::FromSeconds(1);
+  return unthrottled_runtime + one_second -
+         ((unthrottled_runtime - base::TimeTicks()) % one_second);
+}
+
+void TaskQueueThrottler::MaybeSchedulePumpThrottledTasks(
+    const tracked_objects::Location& from_here,
+    base::TimeTicks now,
+    base::TimeTicks unaligned_runtime) {
+  if (virtual_time_)
+    return;
+
+  base::TimeTicks runtime =
+      std::max(now, AlignedThrottledRunTime(unaligned_runtime));
+
+  // If there is a pending call to PumpThrottledTasks and it's sooner than
+  // |runtime| then return.
+  if (pending_pump_throttled_tasks_runtime_ &&
+      runtime >= pending_pump_throttled_tasks_runtime_.value()) {
+    return;
+  }
+
+  pending_pump_throttled_tasks_runtime_ = runtime;
+
+  pump_throttled_tasks_closure_.Cancel();
+
+  base::TimeDelta delay = pending_pump_throttled_tasks_runtime_.value() - now;
+  TRACE_EVENT1(tracing_category_,
+               "TaskQueueThrottler::MaybeSchedulePumpThrottledTasks",
+               "delay_till_next_pump_ms", delay.InMilliseconds());
+  task_runner_->PostDelayedTask(
+      from_here, pump_throttled_tasks_closure_.callback(), delay);
+}
+
+void TaskQueueThrottler::EnableVirtualTime() {
+  virtual_time_ = true;
+
+  pump_throttled_tasks_closure_.Cancel();
+
+  for (auto it = queue_details_.begin(); it != queue_details_.end();) {
+    TaskQueue* task_queue = it->first;
+    bool enabled = it->second.enabled;
+
+    if (!it->second.time_budget_pool) {
+      it = queue_details_.erase(it);
+    } else {
+      // Fall back to default values.
+      it->second.throttling_ref_count = 0;
+      it->second.enabled = false;
+      it++;
+    }
+
+    task_queue->SetTimeDomain(renderer_scheduler_->GetVirtualTimeDomain());
+    task_queue->RemoveFence();
+    task_queue->SetQueueEnabled(enabled);
+  }
+}
+
+TaskQueueThrottler::TimeBudgetPool* TaskQueueThrottler::CreateTimeBudgetPool(
+    const char* name) {
+  TimeBudgetPool* time_budget_pool =
+      new TimeBudgetPool(name, this, tick_clock_->NowTicks());
+  time_budget_pools_[time_budget_pool] = base::WrapUnique(time_budget_pool);
+  return time_budget_pool;
+}
+
+void TaskQueueThrottler::OnTaskRunTimeReported(TaskQueue* task_queue,
+                                               base::TimeTicks start_time,
+                                               base::TimeTicks end_time) {
+  if (!IsThrottled(task_queue))

[alex clarke (OOO till 29th), 2016/09/16 15:23:38]

Just want to make sure I understand this.  Is it possible for a queue to be in a
TimeBudgetPool but not be throttled?

If so is this check the right thing to do?

[altimin, 2016/09/16 16:32:25]

Yes, yes.

Example use case: we have a common time budget pool for offscreen frames and
we're throttling only ones which are offscreen. Onscreen frames are added to
same budget pool but not throttled.

+    return;
+
+  TimeBudgetPool* time_budget_pool = GetTimeBudgetPoolForQueue(task_queue);
+  if (!time_budget_pool)
+    return;
+
+  time_budget_pool->RecordTaskRunTime(end_time - start_time);
+  if (!time_budget_pool->HasEnoughBudgetToRun(end_time))
+    time_budget_pool->BlockQueues(end_time);
+}
+
+void TaskQueueThrottler::AsValueInto(base::trace_event::TracedValue* state,
+                                     base::TimeTicks now) const {
+  if (pending_pump_throttled_tasks_runtime_) {
+    state->SetDouble(
+        "next_throttled_tasks_pump_in_seconds",
+        (pending_pump_throttled_tasks_runtime_.value() - now).InSecondsF());
+  }
+
+  state->BeginDictionary("time_budget_pools");
+
+  for (const auto& map_entry : time_budget_pools_) {
+    TaskQueueThrottler::TimeBudgetPool* pool = map_entry.first;
+    pool->AsValueInto(state, now);
+  }
+
+  state->EndDictionary();
+}
+
+TaskQueueThrottler::TimeBudgetPool*
+TaskQueueThrottler::GetTimeBudgetPoolForQueue(TaskQueue* queue) {
+  auto find_it = queue_details_.find(queue);
+  if (find_it == queue_details_.end()) {
+    return nullptr;
+  } else {
+    return find_it->second.time_budget_pool;
+  }
+}
+
+void TaskQueueThrottler::MaybeSchedulePumpQueue(
+    const tracked_objects::Location& from_here,
+    base::TimeTicks now,
+    TaskQueue* queue,
+    base::Optional<base::TimeTicks> next_possible_run_time) {
+  LazyNow lazy_now(now);
+  base::Optional<base::TimeTicks> next_run_time =
+      Max(NextTaskRunTime(&lazy_now, queue), next_possible_run_time);
+
+  if (next_run_time) {
+    MaybeSchedulePumpThrottledTasks(from_here, now, next_run_time.value());
+  }
+}
+
+base::TimeTicks TaskQueueThrottler::GetNextAllowedRunTime(base::TimeTicks now,
+                                                          TaskQueue* queue) {
+  TimeBudgetPool* time_budget_pool = GetTimeBudgetPoolForQueue(queue);
+  if (!time_budget_pool) {
+    return now;
+  } else {
+    return std::max(now, time_budget_pool->GetNextAllowedRunTime());
+  }
+}
+
+void TaskQueueThrottler::MaybeDeleteQueueMetadata(TaskQueueMap::iterator it) {
+  if (it->second.throttling_ref_count == 0 && !it->second.time_budget_pool)
+    queue_details_.erase(it);
+}
+
+}  // namespace scheduler
+}  // namespace blink