[task] Create kMaxDelayedStarvationTasks feature param

Bug: 1153139 Change-Id: I90c8a1d1c42d005337833cf327f0e852e5cdc24e Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4327433 Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org> Reviewed-by: Francois Pierre Doray <fdoray@chromium.org> Cr-Commit-Position: refs/heads/main@{#1117734}
chromium · Mar 15, 2023 · e9957c9 · e9957c9
1 parent 1150229
commit e9957c9
Show file tree

Hide file tree

Showing 5 changed files with 32 additions and 2 deletions.
diff --git a/base/task/sequence_manager/sequence_manager_impl.cc b/base/task/sequence_manager/sequence_manager_impl.cc
@@ -296,6 +296,7 @@ void SequenceManagerImpl::InitializeFeatures() {
   g_explicit_high_resolution_timer_win =
       FeatureList::IsEnabled(kExplicitHighResolutionTimerWin);
 #endif  // BUILDFLAG(IS_WIN)
+  TaskQueueSelector::InitializeFeatures();
 }
 
 // static

diff --git a/base/task/sequence_manager/task_queue_selector.cc b/base/task/sequence_manager/task_queue_selector.cc
@@ -11,6 +11,7 @@
 #include "base/task/sequence_manager/associated_thread_id.h"
 #include "base/task/sequence_manager/task_queue_impl.h"
 #include "base/task/sequence_manager/work_queue.h"
+#include "base/task/task_features.h"
 #include "base/threading/thread_checker.h"
 #include "base/trace_event/base_tracing.h"
 #include "third_party/abseil-cpp/absl/types/optional.h"
@@ -19,6 +20,9 @@ namespace base {
 namespace sequence_manager {
 namespace internal {
 
+std::atomic_int TaskQueueSelector::g_max_delayed_starvation_tasks =
+    TaskQueueSelector::kDefaultMaxDelayedStarvationTasks;
+
 TaskQueueSelector::TaskQueueSelector(
     scoped_refptr<const AssociatedThreadId> associated_thread,
     const SequenceManager::Settings& settings)
@@ -34,6 +38,12 @@ TaskQueueSelector::TaskQueueSelector(
 
 TaskQueueSelector::~TaskQueueSelector() = default;
 
+// static
+void TaskQueueSelector::InitializeFeatures() {
+  g_max_delayed_starvation_tasks.store(kMaxDelayedStarvationTasksParam.Get(),
+                                       std::memory_order_relaxed);
+}
+
 void TaskQueueSelector::AddQueue(internal::TaskQueueImpl* queue,
                                  TaskQueue::QueuePriority priority) {
   DCHECK_CALLED_ON_VALID_THREAD(associated_thread_->thread_checker);

diff --git a/base/task/sequence_manager/task_queue_selector.h b/base/task/sequence_manager/task_queue_selector.h
@@ -7,6 +7,7 @@
 
 #include <stddef.h>
 
+#include <atomic>
 #include <vector>
 
 #include "base/base_export.h"
@@ -39,6 +40,8 @@ class BASE_EXPORT TaskQueueSelector : public WorkQueueSets::Observer {
   TaskQueueSelector& operator=(const TaskQueueSelector&) = delete;
   ~TaskQueueSelector() override;
 
+  static void InitializeFeatures();
+
   // Called to register a queue that can be selected. This function is called
   // on the main thread.
   void AddQueue(internal::TaskQueueImpl* queue,
@@ -108,7 +111,7 @@ class BASE_EXPORT TaskQueueSelector : public WorkQueueSets::Observer {
 
   // Maximum number of delayed tasks tasks which can be run while there's a
   // waiting non-delayed task.
-  static const int kMaxDelayedStarvationTasks = 3;
+  static const int kDefaultMaxDelayedStarvationTasks = 3;
 
   // Tracks which priorities are currently active, meaning there are pending
   // runnable tasks with that priority. Because there are only a handful of
@@ -167,7 +170,7 @@ class BASE_EXPORT TaskQueueSelector : public WorkQueueSets::Observer {
   template <typename SetOperation>
   WorkQueue* ChooseWithPriority(TaskQueue::QueuePriority priority) const {
     // Select an immediate work queue if we are starving immediate tasks.
-    if (immediate_starvation_count_ >= kMaxDelayedStarvationTasks) {
+    if (immediate_starvation_count_ >= g_max_delayed_starvation_tasks) {
       WorkQueue* queue =
           ChooseImmediateOnlyWithPriority<SetOperation>(priority);
       if (queue)
@@ -240,6 +243,9 @@ class BASE_EXPORT TaskQueueSelector : public WorkQueueSets::Observer {
   std::vector<int> non_empty_set_counts_;
 
   static constexpr const int kMaxNonEmptySetCount = 2;
+  // An atomic is used here because InitializeFeatures() can race with
+  // SequenceManager reading this.
+  static std::atomic_int g_max_delayed_starvation_tasks;
 
   // List of active priorities, which is used to work out which priority to run
   // next.

diff --git a/base/task/task_features.cc b/base/task/task_features.cc
@@ -85,4 +85,11 @@ BASE_EXPORT TimeDelta GetDefaultTaskLeeway() {
   return g_task_leeway.load(std::memory_order_relaxed);
 }
 
+BASE_FEATURE(kMaxDelayedStarvationTasks,
+             "MaxDelayedStarvationTasks",
+             base::FEATURE_ENABLED_BY_DEFAULT);
+
+const base::FeatureParam<int> kMaxDelayedStarvationTasksParam{
+    &kMaxDelayedStarvationTasks, "count", 3};
+
 }  // namespace base
diff --git a/base/task/task_features.h b/base/task/task_features.h
@@ -59,6 +59,12 @@ BASE_EXPORT void InitializeTaskLeeway();
 BASE_EXPORT TimeDelta GetTaskLeewayForCurrentThread();
 BASE_EXPORT TimeDelta GetDefaultTaskLeeway();
 
+// Controls the max number of delayed tasks that can run before selecting an
+// immediate task in sequence manager.
+BASE_EXPORT BASE_DECLARE_FEATURE(kMaxDelayedStarvationTasks);
+extern const BASE_EXPORT base::FeatureParam<int>
+    kMaxDelayedStarvationTasksParam;
+
 }  // namespace base
 
 #endif  // BASE_TASK_TASK_FEATURES_H_