Support computing percentiles on a rolling window of samples

cc/scheduler/rolling_time_delta_history_unittest.cc

+// Copyright 2013 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 "cc/scheduler/rolling_time_delta_history.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cc {
+namespace {
+
+TEST(RollingTimeDeltaHistoryTest, EmptyHistory) {
+  RollingTimeDeltaHistory empty_history(0);
+
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(0.0));
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(50.0));
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(100.0));
+
+  empty_history.InsertSample(base::TimeDelta::FromMilliseconds(10));
+  empty_history.InsertSample(base::TimeDelta::FromMilliseconds(15));
+  empty_history.InsertSample(base::TimeDelta::FromMilliseconds(20));
+
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(0.0));
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(50.0));
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(100.0));
+
+  empty_history.Clear();
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(0.0));
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(50.0));
+  EXPECT_EQ(base::TimeDelta(), empty_history.Percentile(100.0));
+}
+
+TEST(RollingTimeDeltaHistoryTest, SizeOneHistory) {
+  RollingTimeDeltaHistory size_one_history(1);
+  base::TimeDelta sample1 = base::TimeDelta::FromMilliseconds(10);
+  base::TimeDelta sample2 = base::TimeDelta::FromMilliseconds(20);
+
+  EXPECT_EQ(base::TimeDelta(), size_one_history.Percentile(0.0));
+  EXPECT_EQ(base::TimeDelta(), size_one_history.Percentile(50.0));
+  EXPECT_EQ(base::TimeDelta(), size_one_history.Percentile(100.0));
+
+  size_one_history.InsertSample(sample1);
+  EXPECT_EQ(sample1, size_one_history.Percentile(0.0));
+  EXPECT_EQ(sample1, size_one_history.Percentile(50.0));
+  EXPECT_EQ(sample1, size_one_history.Percentile(100.0));
+
+  size_one_history.InsertSample(sample2);
+  EXPECT_EQ(sample2, size_one_history.Percentile(0.0));
+  EXPECT_EQ(sample2, size_one_history.Percentile(50.0));
+  EXPECT_EQ(sample2, size_one_history.Percentile(100.0));
+
+  size_one_history.Clear();
+  EXPECT_EQ(base::TimeDelta(), size_one_history.Percentile(0.0));
+  EXPECT_EQ(base::TimeDelta(), size_one_history.Percentile(50.0));
+  EXPECT_EQ(base::TimeDelta(), size_one_history.Percentile(100.0));
+}
+
+TEST(RollingTimeDeltaHistoryTest, LargeHistory) {
+  RollingTimeDeltaHistory large_history(100);
+  base::TimeDelta sample1 = base::TimeDelta::FromMilliseconds(150);
+  base::TimeDelta sample2 = base::TimeDelta::FromMilliseconds(250);
+  base::TimeDelta sample3 = base::TimeDelta::FromMilliseconds(200);
+
+  large_history.InsertSample(sample1);
+  large_history.InsertSample(sample2);
+
+  EXPECT_EQ(sample1, large_history.Percentile(0.0));
+  EXPECT_EQ(sample1, large_history.Percentile(25.0));
+  EXPECT_EQ(sample2, large_history.Percentile(75.0));
+  EXPECT_EQ(sample2, large_history.Percentile(100.0));
+
+  large_history.InsertSample(sample3);
+  EXPECT_EQ(sample1, large_history.Percentile(0.0));
+  EXPECT_EQ(sample1, large_history.Percentile(25.0));
+  EXPECT_EQ(sample3, large_history.Percentile(50.0));
+  EXPECT_EQ(sample2, large_history.Percentile(100.0));
+
+  // Fill the history.
+  for (int i = 1; i <= 97; i++)
+    large_history.InsertSample(base::TimeDelta::FromMilliseconds(i));
+
+  EXPECT_EQ(base::TimeDelta::FromMilliseconds(1),
+            large_history.Percentile(0.0));
+  for (int i = 1; i <= 97; i++) {
+    EXPECT_EQ(base::TimeDelta::FromMilliseconds(i),
+              large_history.Percentile(i - 0.5));
+  }
+  EXPECT_EQ(sample1, large_history.Percentile(97.5));
+  EXPECT_EQ(sample3, large_history.Percentile(98.5));
+  EXPECT_EQ(sample2, large_history.Percentile(99.5));
+
+  // Continue inserting samples, causing the oldest samples to be discarded.
+  base::TimeDelta sample4 = base::TimeDelta::FromMilliseconds(100);
+  base::TimeDelta sample5 = base::TimeDelta::FromMilliseconds(102);
+  base::TimeDelta sample6 = base::TimeDelta::FromMilliseconds(104);
+  large_history.InsertSample(sample4);
+  large_history.InsertSample(sample5);
+  large_history.InsertSample(sample6);
+  EXPECT_EQ(sample4, large_history.Percentile(97.5));
+  EXPECT_EQ(sample5, large_history.Percentile(98.5));
+  EXPECT_EQ(sample6, large_history.Percentile(99.5));
+
+  large_history.Clear();
+  EXPECT_EQ(base::TimeDelta(), large_history.Percentile(0.0));
+  EXPECT_EQ(base::TimeDelta(), large_history.Percentile(50.0));
+  EXPECT_EQ(base::TimeDelta(), large_history.Percentile(100.0));
+}
+
+}  // namespace
+}  // namespace cc