Add CPU reduction experiment.

This CL has two parts:

Part 1: This CL adds an experiment to base called
IsRunningCpuReductionExperiment. When enabled, several different
unrelated features will change their behavior to reduce overall CPU
consumption of chrome. As these features are unrelated, this experiment
must live in base as the only common dependency.

Part 2: This CL modifies 6 functions that emit UMA metrics to emit at
1/1000th of their current rate. Combined, the UMA metric emission from
these 6 functions are responsible for 0.33% of all CPU cycles on
ChromeOS, including time from non-chrome processes. This demonstrates
why the code in part 1 must live in base.

Future CLs will add more CPU-savings to the experiment before it is
enabled.

Bug: 1295441
Change-Id: I8202c5a1482ff66fc90a7bc64bb36b3cdc773130
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3449251
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#969512}

base/BUILD.gn

@@ -278,6 +278,8 @@ mixed_component("base") {
     "containers/vector_buffer.h",
     "cpu.cc",
     "cpu.h",
+    "cpu_reduction_experiment.cc",
+    "cpu_reduction_experiment.h",
     "critical_closure.h",
     "cxx17_backports.h",
     "cxx20_to_address.h",

base/cpu_reduction_experiment.cc

@@ -0,0 +1,40 @@
+// Copyright 2022 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 "base/cpu_reduction_experiment.h"
+
+#include "base/feature_list.h"
+
+namespace base {
+
+namespace {
+
+// This feature controls whether to enable a series of optimizations that
+// reduces total CPU utilization of chrome.
+constexpr Feature kReduceCpuUtilization{"ReduceCpuUtilization",
+                                        FEATURE_DISABLED_BY_DEFAULT};
+
+// Cache of the state of the ReduceCpuUtilization feature. This avoids the need
+// to constantly query its enabled state through FeatureList::IsEnabled().
+bool g_is_reduce_cpu_enabled =
+    kReduceCpuUtilization.default_state == FEATURE_ENABLED_BY_DEFAULT;
+
+}  // namespace
+
+bool IsRunningCpuReductionExperiment() {
+  return g_is_reduce_cpu_enabled;
+}
+
+void InitializeCpuReductionExperiment() {
+  g_is_reduce_cpu_enabled = FeatureList::IsEnabled(kReduceCpuUtilization);
+}
+
+bool CpuReductionExperimentFilter::ShouldLogHistograms() {
+  if (!IsRunningCpuReductionExperiment())
+    return true;
+
+  return (++counter_ % 1000) == 1;
+}
+
+}  // namespace base

base/cpu_reduction_experiment.h

@@ -0,0 +1,35 @@
+// Copyright 2022 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.
+
+#ifndef BASE_CPU_REDUCTION_EXPERIMENT_H_
+#define BASE_CPU_REDUCTION_EXPERIMENT_H_
+
+#include "base/base_export.h"
+
+namespace base {
+
+// Returns whether the cpu cycle reduction experiment is running.
+// The goal of this experiment is to better understand the relationship between
+// total CPU cycles used across the fleet and top-line chrome metrics.
+BASE_EXPORT bool IsRunningCpuReductionExperiment();
+
+// Must be called after FeatureList initialization and while chrome is still
+// single-threaded.
+BASE_EXPORT void InitializeCpuReductionExperiment();
+
+// This is a helper class to reduce common duplicate code. If the CPU reduction
+// experiment is running, then ShouldLogHistograms returns true on every 1000th
+// call. Otherwise it always returns true.
+class BASE_EXPORT CpuReductionExperimentFilter {
+ public:
+  // Returns true on the first call, and every 1000th call after that.
+  bool ShouldLogHistograms();
+
+ private:
+  int counter_ = 0;
+};
+
+}  // namespace base
+
+#endif  // BASE_CPU_REDUCTION_EXPERIMENT_H_

cc/metrics/compositor_frame_reporter.cc

@@ -9,6 +9,7 @@
 #include <string>
 #include <utility>
 
+#include "base/cpu_reduction_experiment.h"
 #include "base/cxx17_backports.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/strcat.h"
@@ -819,6 +820,9 @@ void CompositorFrameReporter::EndCurrentStage(base::TimeTicks end_time) {
 }
 
 void CompositorFrameReporter::ReportCompositorLatencyHistograms() const {
+  static base::CpuReductionExperimentFilter filter;
+  if (!filter.ShouldLogHistograms())
+    return;
   for (const StageData& stage : stage_history_) {
     ReportStageHistogramWithBreakdown(stage);
     for (size_t type = 0; type < active_trackers_.size(); ++type) {

chrome/app/chrome_main_delegate.cc

@@ -11,6 +11,7 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/cpu.h"
+#include "base/cpu_reduction_experiment.h"
 #include "base/cxx17_backports.h"
 #include "base/dcheck_is_on.h"
 #include "base/files/file_path.h"
@@ -732,6 +733,7 @@ void ChromeMainDelegate::PostFieldTrialInitialization() {
   base::HangWatcher::InitializeOnMainThread(hang_watcher_process_type);
 
   base::internal::TimerBase::InitializeFeatures();
+  base::InitializeCpuReductionExperiment();
   base::sequence_manager::internal::SequenceManagerImpl::InitializeFeatures();
 }
 

components/scheduling_metrics/total_duration_metric_reporter.cc

@@ -4,6 +4,8 @@
 
 #include "components/scheduling_metrics/total_duration_metric_reporter.h"
 
+#include "base/cpu_reduction_experiment.h"
+
 namespace scheduling_metrics {
 
 namespace {
@@ -34,6 +36,9 @@ TotalDurationMetricReporter::~TotalDurationMetricReporter() = default;
 
 void TotalDurationMetricReporter::RecordAdditionalDuration(
     base::TimeDelta duration) {
+  static base::CpuReductionExperimentFilter filter;
+  if (!filter.ShouldLogHistograms())
+    return;
   if (reported_value_)
     negative_histogram_->Add(reported_value_->InSeconds());
   reported_value_ = reported_value_.value_or(base::TimeDelta()) + duration;

gpu/command_buffer/service/scheduler.cc

@@ -10,6 +10,7 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
+#include "base/cpu_reduction_experiment.h"
 #include "base/hash/md5_constexpr.h"
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ -612,11 +613,15 @@ Scheduler::RebuildSchedulingQueueIfNeeded(
 }
 
 void Scheduler::RunNextTask() {
+  static base::CpuReductionExperimentFilter filter;
+  bool log_histograms = filter.ShouldLogHistograms();
   base::AutoLock auto_lock(lock_);
-  UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
-      "GPU.Scheduler.ThreadSuspendedTime",
-      base::TimeTicks::Now() - run_next_task_scheduled_, base::Microseconds(10),
-      base::Seconds(30), 100);
+  if (log_histograms) {
+    UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
+        "GPU.Scheduler.ThreadSuspendedTime",
+        base::TimeTicks::Now() - run_next_task_scheduled_,
+        base::Microseconds(10), base::Seconds(30), 100);
+  }
   auto* task_runner = base::ThreadTaskRunnerHandle::Get().get();
 
   SchedulingState state;
@@ -641,15 +646,17 @@ void Scheduler::RunNextTask() {
   DCHECK(sequence);
   DCHECK_EQ(sequence->task_runner(), task_runner);
 
-  UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
-      "GPU.Scheduler.TaskDependencyTime",
-      sequence->FrontTaskWaitingDependencyDelta(), base::Microseconds(10),
-      base::Seconds(30), 100);
+  if (log_histograms) {
+    UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
+        "GPU.Scheduler.TaskDependencyTime",
+        sequence->FrontTaskWaitingDependencyDelta(), base::Microseconds(10),
+        base::Seconds(30), 100);
 
-  UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
-      "GPU.Scheduler.TaskSchedulingDelayTime",
-      sequence->FrontTaskSchedulingDelay(), base::Microseconds(10),
-      base::Seconds(30), 100);
+    UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
+        "GPU.Scheduler.TaskSchedulingDelayTime",
+        sequence->FrontTaskSchedulingDelay(), base::Microseconds(10),
+        base::Seconds(30), 100);
+  }
 
   base::OnceClosure closure;
   uint32_t order_num = sequence->BeginTask(&closure);
@@ -703,9 +710,11 @@ void Scheduler::RunNextTask() {
     }
   }
 
-  UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
-      "GPU.Scheduler.RunTaskTime", task_timer.Elapsed(), base::Microseconds(10),
-      base::Seconds(30), 100);
+  if (log_histograms) {
+    UMA_HISTOGRAM_CUSTOM_MICROSECONDS_TIMES(
+        "GPU.Scheduler.RunTaskTime", task_timer.Elapsed(),
+        base::Microseconds(10), base::Seconds(30), 100);
+  }
 
   // Avoid scheduling another RunNextTask if we're done with all tasks.
   auto& scheduling_queue = RebuildSchedulingQueueIfNeeded(task_runner);

mojo/core/channel_posix.cc

@@ -15,6 +15,7 @@
 
 #include "base/bind.h"
 #include "base/containers/queue.h"
+#include "base/cpu_reduction_experiment.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
@@ -153,10 +154,17 @@ void ChannelPosix::ShutDownImpl() {
 }
 
 void ChannelPosix::Write(MessagePtr message) {
-  UMA_HISTOGRAM_COUNTS_100000("Mojo.Channel.WriteMessageSize",
-                              message->data_num_bytes());
-  UMA_HISTOGRAM_COUNTS_100("Mojo.Channel.WriteMessageHandles",
-                           message->NumHandlesForTransit());
+  bool log_histograms = true;
+#if !defined(MOJO_CORE_SHARED_LIBRARY)
+  static base::CpuReductionExperimentFilter filter;
+  log_histograms = filter.ShouldLogHistograms();
+#endif
+  if (log_histograms) {
+    UMA_HISTOGRAM_COUNTS_100000("Mojo.Channel.WriteMessageSize",
+                                message->data_num_bytes());
+    UMA_HISTOGRAM_COUNTS_100("Mojo.Channel.WriteMessageHandles",
+                             message->NumHandlesForTransit());
+  }
 
   bool write_error = false;
   {

third_party/blink/renderer/core/frame/DEPS

@@ -27,6 +27,9 @@ specific_include_rules = {
   "local_frame\.cc": [
     "+ui/gfx/transform.h"
   ],
+  "local_frame_ukm_aggregator\.cc": [
+    "+base/cpu_reduction_experiment.h",
+  ],
   "local_frame_ukm_aggregator_test\.cc": [
     "+base/metrics/statistics_recorder.h"
   ],

third_party/blink/renderer/core/frame/local_frame_ukm_aggregator.cc

@@ -6,6 +6,7 @@
 
 #include <memory>
 
+#include "base/cpu_reduction_experiment.h"
 #include "base/format_macros.h"
 #include "base/numerics/safe_conversions.h"
 #include "base/rand_util.h"
@@ -253,6 +254,10 @@ void LocalFrameUkmAggregator::RecordTimerSample(size_t metric_index,
 
 void LocalFrameUkmAggregator::RecordCountSample(size_t metric_index,
                                                 int64_t count) {
+  static base::CpuReductionExperimentFilter filter;
+  if (!filter.ShouldLogHistograms())
+    return;
+
   // Always use RecordForcedLayoutSample for the kForcedStyleAndLayout
   // metric id.
   DCHECK_NE(metric_index, static_cast<size_t>(kForcedStyleAndLayout));

third_party/blink/tools/blinkpy/presubmit/audit_non_blink_usage.py

@@ -46,6 +46,7 @@
             'base::ApplyMetadataToPastSamples',
             'base::AutoReset',
             'base::Contains',
+            'base::CpuReductionExperimentFilter',
             'base::CreateSequencedTaskRunner',
             'base::ValuesEquivalent',
             'base::Days',

url/url_canon_host.cc

@@ -5,6 +5,7 @@
 #include <unordered_set>
 
 #include "base/check.h"
+#include "base/cpu_reduction_experiment.h"
 #include "base/metrics/histogram_macros.h"
 #include "url/url_canon.h"
 #include "url/url_canon_internal.h"
@@ -177,12 +178,15 @@ bool DoSimpleHost(const INCHAR* host,
     }
   }
   if (success) {
-    bool did_escape = !escaped_chars_to_measure.empty();
-    UMA_HISTOGRAM_BOOLEAN("URL.Host.DidEscape", did_escape);
-    if (did_escape) {
-      for (char c : escaped_chars_to_measure) {
-        UMA_HISTOGRAM_ENUMERATION("URL.Host.EscapeChar",
-                                  EscapedHostCharToEnum(c));
+    static base::CpuReductionExperimentFilter filter;
+    if (filter.ShouldLogHistograms()) {
+      bool did_escape = !escaped_chars_to_measure.empty();
+      UMA_HISTOGRAM_BOOLEAN("URL.Host.DidEscape", did_escape);
+      if (did_escape) {
+        for (char c : escaped_chars_to_measure) {
+          UMA_HISTOGRAM_ENUMERATION("URL.Host.EscapeChar",
+                                    EscapedHostCharToEnum(c));
+        }
       }
     }
   }