[threadpool] Remove ThreadPool.NumTasksRunWhileQueuing histogram.

Historical histogram data is already available in
base/task/thread_pool/historical_histogram_data.md

Bug: 995483
Change-Id: I9c7898627dcd75dc6ffb1bb9b64d60f6a52a21a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446206Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Auto-Submit: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814942}

base/task/thread_pool/service_thread.cc

@@ -81,10 +81,8 @@ void ServiceThread::PerformHeartbeatLatencyReport() const {
   // reported latency.
   ThreadPool::PostTask(
       FROM_HERE, {profiled_priority},
-      BindOnce(
-          &TaskTracker::RecordHeartbeatLatencyAndTasksRunWhileQueuingHistograms,
-          Unretained(task_tracker_), profiled_priority, TimeTicks::Now(),
-          task_tracker_->GetNumTasksRun()));
+      BindOnce(&TaskTracker::RecordHeartbeatLatencyHistogram,
+               Unretained(task_tracker_), profiled_priority, TimeTicks::Now()));
 }
 
 }  // namespace internal

base/task/thread_pool/task_tracker.cc

@@ -102,27 +102,6 @@ HistogramBase* GetLatencyHistogram(StringPiece histogram_name,
       HistogramBase::kUmaTargetedHistogramFlag);
 }
 
-// Constructs a histogram to track task count which is logging to
-// "ThreadPool.{histogram_name}.{histogram_label}.{task_type_suffix}".
-HistogramBase* GetCountHistogram(StringPiece histogram_name,
-                                 StringPiece histogram_label,
-                                 StringPiece task_type_suffix) {
-  DCHECK(!histogram_name.empty());
-  DCHECK(!task_type_suffix.empty());
-
-  if (histogram_label.empty())
-    return nullptr;
-
-  // Mimics the UMA_HISTOGRAM_CUSTOM_COUNTS macro.
-  const std::string histogram = JoinString(
-      {"ThreadPool", histogram_name, histogram_label, task_type_suffix}, ".");
-  // 500 was chosen as the maximum number of tasks run while queuing because
-  // values this high would likely indicate an error, beyond which knowing the
-  // actual number of tasks is not informative.
-  return Histogram::FactoryGet(histogram, 1, 500, 50,
-                               HistogramBase::kUmaTargetedHistogramFlag);
-}
-
 // Returns a histogram stored in an array indexed by task priority.
 // TODO(jessemckenna): use the STATIC_HISTOGRAM_POINTER_GROUP macro from
 // histogram_macros.h instead.
@@ -336,16 +315,6 @@ TaskTracker::TaskTracker(StringPiece histogram_label)
           GetLatencyHistogram("HeartbeatLatencyMicroseconds",
                               histogram_label,
                               "UserBlockingTaskPriority")},
-      num_tasks_run_while_queuing_histograms_{
-          GetCountHistogram("NumTasksRunWhileQueuing",
-                            histogram_label,
-                            "BackgroundTaskPriority"),
-          GetCountHistogram("NumTasksRunWhileQueuing",
-                            histogram_label,
-                            "UserVisibleTaskPriority"),
-          GetCountHistogram("NumTasksRunWhileQueuing",
-                            histogram_label,
-                            "UserBlockingTaskPriority")},
       tracked_ref_factory_(this) {}
 
 TaskTracker::~TaskTracker() = default;
@@ -532,27 +501,14 @@ void TaskTracker::RecordLatencyHistogram(TaskPriority priority,
       ->AddTimeMicrosecondsGranularity(task_latency);
 }
 
-void TaskTracker::RecordHeartbeatLatencyAndTasksRunWhileQueuingHistograms(
-    TaskPriority priority,
-    TimeTicks posted_time,
-    int num_tasks_run_when_posted) const {
+void TaskTracker::RecordHeartbeatLatencyHistogram(TaskPriority priority,
+                                                  TimeTicks posted_time) const {
   if (histogram_label_.empty())
     return;
 
   const TimeDelta task_latency = TimeTicks::Now() - posted_time;
   GetHistogramForTaskPriority(priority, heartbeat_latency_histograms_)
       ->AddTimeMicrosecondsGranularity(task_latency);
-
-  GetHistogramForTaskPriority(priority, num_tasks_run_while_queuing_histograms_)
-      ->Add(GetNumTasksRun() - num_tasks_run_when_posted);
-}
-
-int TaskTracker::GetNumTasksRun() const {
-  return num_tasks_run_.load(std::memory_order_relaxed);
-}
-
-void TaskTracker::IncrementNumTasksRun() {
-  num_tasks_run_.fetch_add(1, std::memory_order_relaxed);
 }
 
 void TaskTracker::RunTask(Task task,
@@ -709,7 +665,6 @@ bool TaskTracker::BeforeRunTask(TaskShutdownBehavior shutdown_behavior) {
 }
 
 void TaskTracker::AfterRunTask(TaskShutdownBehavior shutdown_behavior) {
-  IncrementNumTasksRun();
   if (shutdown_behavior == TaskShutdownBehavior::SKIP_ON_SHUTDOWN) {
     DecrementNumItemsBlockingShutdown();
   }

base/task/thread_pool/task_tracker.h

@@ -130,20 +130,12 @@ class BASE_EXPORT TaskTracker {
   // no tasks are blocking shutdown).
   bool IsShutdownComplete() const;
 
-  // Records two histograms
-  // 1. ThreadPool.[label].HeartbeatLatencyMicroseconds.[suffix]:
-  //    Now() - posted_time
-  // 2. ThreadPool.[label].NumTasksRunWhileQueuing.[suffix]:
-  //    GetNumTasksRun() - num_tasks_run_when_posted.
+  // Records Now() - posted_time to
+  // ThreadPool.[label].HeartbeatLatencyMicroseconds.[suffix].
   // [label] is the histogram label provided to the constructor.
   // [suffix] is derived from |task_priority|.
-  void RecordHeartbeatLatencyAndTasksRunWhileQueuingHistograms(
-      TaskPriority task_priority,
-      TimeTicks posted_time,
-      int num_tasks_run_when_posted) const;
-
-  // Returns the number of tasks run so far
-  int GetNumTasksRun() const;
+  void RecordHeartbeatLatencyHistogram(TaskPriority task_priority,
+                                       TimeTicks posted_time) const;
 
   TrackedRef<TaskTracker> GetTrackedRef() {
     return tracked_ref_factory_.GetTrackedRef();
@@ -206,8 +198,6 @@ class BASE_EXPORT TaskTracker {
   void RecordLatencyHistogram(TaskPriority priority,
                               TimeTicks posted_time) const;
 
-  void IncrementNumTasksRun();
-
   // Dummy frames to allow identification of shutdown behavior in a stack trace.
   void RunContinueOnShutdown(Task* task);
   void RunSkipOnShutdown(Task* task);
@@ -263,10 +253,6 @@ class BASE_EXPORT TaskTracker {
   // completes.
   std::unique_ptr<WaitableEvent> shutdown_event_ GUARDED_BY(shutdown_lock_);
 
-  // Counter for number of tasks run so far, used to record tasks run while
-  // a task queued to histogram.
-  std::atomic_int num_tasks_run_{0};
-
   // ThreadPool.TaskLatencyMicroseconds.*,
   // ThreadPool.HeartbeatLatencyMicroseconds.*, and
   // ThreadPool.NumTasksRunWhileQueuing.* histograms. The index is a
@@ -278,8 +264,6 @@ class BASE_EXPORT TaskTracker {
       static_cast<TaskPriorityType>(TaskPriority::HIGHEST) + 1;
   HistogramBase* const task_latency_histograms_[kNumTaskPriorities];
   HistogramBase* const heartbeat_latency_histograms_[kNumTaskPriorities];
-  HistogramBase* const
-      num_tasks_run_while_queuing_histograms_[kNumTaskPriorities];
 
   // Ensures all state (e.g. dangling cleaned up workers) is coalesced before
   // destroying the TaskTracker (e.g. in test environments).

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -14818,6 +14818,9 @@ should be kept until we remove incident reporting. -->
 
 <histogram base="true" name="ThreadPool.NumTasksRunWhileQueuing" units="tasks"
     expires_after="2019-10-01">
+  <obsolete>
+    Removed 10/2020. Not actively used.
+  </obsolete>
   <owner>fdoray@chromium.org</owner>
   <summary>
     Number of tasks run by ThreadPool while task was queuing (from time task was