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// Copyright 2022 The Chromium Authors
// 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 <atomic>
#include "base/check.h"
#include "base/dcheck_is_on.h"
#include "base/feature_list.h"
#include "base/rand_util.h"
#include "base/synchronization/lock.h"
#include "base/thread_annotations.h"
namespace base {
namespace {
// Whether to enable a series of optimizations that reduce total CPU
// utilization.
BASE_FEATURE(kReduceCpuUtilization,
"ReduceCpuUtilization",
FEATURE_DISABLED_BY_DEFAULT);
class CpuReductionExperimentSubSampler {
public:
CpuReductionExperimentSubSampler() = default;
bool ShouldLogHistograms() {
AutoLock hold(lock_);
return sub_sampler_.ShouldSample(0.001);
}
private:
Lock lock_;
MetricsSubSampler sub_sampler_ GUARDED_BY(lock_);
};
// Singleton instance of CpuReductionExperimentSubSampler. This is only set when
// the ReduceCpuUtilization experiment is enabled -- as a result, it's ok to
// assume that the experiment is disabled when this is not set.
CpuReductionExperimentSubSampler* g_subsampler = nullptr;
#if DCHECK_IS_ON()
// Atomic to support concurrent writes from IsRunningCpuReductionExperiment().
std::atomic_bool g_accessed_subsampler = false;
#endif
} // namespace
bool IsRunningCpuReductionExperiment() {
#if DCHECK_IS_ON()
g_accessed_subsampler.store(true, std::memory_order_seq_cst);
#endif
return !!g_subsampler;
}
void InitializeCpuReductionExperiment() {
#if DCHECK_IS_ON()
// TSAN should generate an error if InitializeCpuReductionExperiment() races
// with IsRunningCpuReductionExperiment().
DCHECK(!g_accessed_subsampler.load(std::memory_order_seq_cst));
#endif
if (FeatureList::IsEnabled(kReduceCpuUtilization)) {
g_subsampler = new CpuReductionExperimentSubSampler();
}
}
bool ShouldLogHistogramForCpuReductionExperiment() {
if (!IsRunningCpuReductionExperiment())
return true;
return g_subsampler->ShouldLogHistograms();
}
} // namespace base
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