base/cpu_reduction_experiment.cc

   1 // Copyright 2022 The Chromium Authors
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/cpu_reduction_experiment.h"
   6
   7 #include <atomic>
   8
   9 #include "base/check.h"
  10 #include "base/dcheck_is_on.h"
  11 #include "base/feature_list.h"
  12 #include "base/rand_util.h"
  13 #include "base/synchronization/lock.h"
  14 #include "base/thread_annotations.h"
  15
  16 namespace base {
  17
  18 namespace {
  19
  20 // Whether to enable a series of optimizations that reduce total CPU
  21 // utilization.
  22 BASE_FEATURE(kReduceCpuUtilization,
  23              "ReduceCpuUtilization2",
  24              FEATURE_ENABLED_BY_DEFAULT);
  25
  26 class CpuReductionExperimentSubSampler {
  27  public:
  28   CpuReductionExperimentSubSampler() = default;
  29
  30   bool ShouldLogHistograms() {
  31     AutoLock hold(lock_);
  32     return sub_sampler_.ShouldSample(0.001);
  33   }
  34
  35  private:
  36   Lock lock_;
  37   MetricsSubSampler sub_sampler_ GUARDED_BY(lock_);
  38 };
  39
  40 // Singleton instance of CpuReductionExperimentSubSampler. This is only set when
  41 // the ReduceCpuUtilization experiment is enabled -- as a result, it's ok to
  42 // assume that the experiment is disabled when this is not set.
  43 CpuReductionExperimentSubSampler* g_subsampler = nullptr;
  44
  45 #if DCHECK_IS_ON()
  46 // Atomic to support concurrent writes from IsRunningCpuReductionExperiment().
  47 std::atomic_bool g_accessed_subsampler = false;
  48 #endif
  49
  50 }  // namespace
  51
  52 bool IsRunningCpuReductionExperiment() {
  53 #if DCHECK_IS_ON()
  54   g_accessed_subsampler.store(true, std::memory_order_seq_cst);
  55 #endif
  56   return !!g_subsampler;
  57 }
  58
  59 void InitializeCpuReductionExperiment() {
  60 #if DCHECK_IS_ON()
  61   // TSAN should generate an error if InitializeCpuReductionExperiment() races
  62   // with IsRunningCpuReductionExperiment().
  63   DCHECK(!g_accessed_subsampler.load(std::memory_order_seq_cst));
  64 #endif
  65   if (FeatureList::IsEnabled(kReduceCpuUtilization)) {
  66     g_subsampler = new CpuReductionExperimentSubSampler();
  67   }
  68 }
  69
  70 bool ShouldLogHistogramForCpuReductionExperiment() {
  71   if (!IsRunningCpuReductionExperiment())
  72     return true;
  73   return g_subsampler->ShouldLogHistograms();
  74 }
  75
  76 }  // namespace base