Index: components/scheduler/base/queueing_time_estimator.cc |
diff --git a/components/scheduler/base/queueing_time_estimator.cc b/components/scheduler/base/queueing_time_estimator.cc |
new file mode 100644 |
index 0000000000000000000000000000000000000000..1402380f5721e24ceb34ae9b87ca5785ed565760 |
--- /dev/null |
+++ b/components/scheduler/base/queueing_time_estimator.cc |
@@ -0,0 +1,87 @@ |
+// Copyright 2016 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 "components/scheduler/base/queueing_time_estimator.h" |
+ |
+#include "base/time/default_tick_clock.h" |
+ |
+namespace scheduler { |
+ |
+namespace { |
+ |
+// This method computes the expected queueing time of a randomly distributed |
+// task R within a window containing a single task T. Let T' be the time range |
+// for which T overlaps the window. We first compute the probability that R will |
+// start within T'. We then compute the expected queueing duration if R does |
+// start within this range. Since the start time of R is uniformly distributed |
+// within the window, this is equal to the average of the queueing times if R |
+// started at the beginning or end of T'. The expected queueing time of T is the |
+// probability that R will start within T', multiplied by the expected queueing |
+// duration if R does fall in this range. |
+base::TimeDelta ExpectedQueueingTimeFromTask(base::TimeTicks task_start, |
+ base::TimeTicks task_end, |
+ base::TimeTicks window_start, |
+ base::TimeTicks window_end) { |
+ DCHECK(task_start <= task_end); |
+ DCHECK(task_start <= window_end); |
+ DCHECK(window_start < window_end); |
+ DCHECK(task_end >= window_start); |
+ base::TimeTicks task_in_window_start_time = |
+ std::max(task_start, window_start); |
+ base::TimeTicks task_in_window_end_time = |
+ std::min(task_end, window_end); |
+ DCHECK(task_in_window_end_time <= task_in_window_end_time); |
+ |
+ double probability_of_this_task = |
+ static_cast<double>((task_in_window_end_time - task_in_window_start_time) |
+ .InMicroseconds()) / |
+ (window_end - window_start).InMicroseconds(); |
+ |
+ base::TimeDelta expected_queueing_duration_within_task = |
+ ((task_end - task_in_window_start_time) + |
+ (task_end - task_in_window_end_time)) / |
+ 2; |
+ |
+ return base::TimeDelta::FromMillisecondsD( |
+ probability_of_this_task * |
+ expected_queueing_duration_within_task.InMillisecondsF()); |
+} |
+ |
+} // namespace |
+ |
+QueueingTimeEstimator::QueueingTimeEstimator( |
+ QueueingTimeEstimator::Client* client, |
+ base::TimeDelta window_duration) |
+ : client_(client), |
+ window_duration_(window_duration), |
+ window_start_time_() {} |
+ |
+void QueueingTimeEstimator::OnToplevelTaskCompleted( |
+ base::TimeTicks task_start_time, |
+ base::TimeTicks task_end_time) { |
+ if (window_start_time_.is_null()) |
+ window_start_time_ = task_start_time; |
+ |
+ while (TimePastWindowEnd(task_end_time)) { |
+ if (!TimePastWindowEnd(task_start_time)) { |
+ // Include the current task in this window. |
+ current_expected_queueing_time_ += ExpectedQueueingTimeFromTask( |
+ task_start_time, task_end_time, window_start_time_, |
+ window_start_time_ + window_duration_); |
+ } |
+ client_->OnQueueingTimeForWindowEstimated(current_expected_queueing_time_); |
+ window_start_time_ += window_duration_; |
+ current_expected_queueing_time_ = base::TimeDelta(); |
+ } |
+ |
+ current_expected_queueing_time_ += ExpectedQueueingTimeFromTask( |
+ task_start_time, task_end_time, window_start_time_, |
+ window_start_time_ + window_duration_); |
+} |
+ |
+bool QueueingTimeEstimator::TimePastWindowEnd(base::TimeTicks time) { |
+ return time > window_start_time_ + window_duration_; |
+} |
+ |
+} // namespace scheduler |