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base / cpu_reduction_experiment.cc [blame]
// 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"
namespace base {
namespace {
// Whether to enable a series of optimizations that reduce total CPU
// utilization.
BASE_FEATURE(kReduceCpuUtilization,
"ReduceCpuUtilization2",
FEATURE_ENABLED_BY_DEFAULT);
class CpuReductionExperimentSubSampler {
public:
CpuReductionExperimentSubSampler() : counter_(base::RandUint64()) {}
bool ShouldLogHistograms() {
// Relaxed memory order since there is no dependent memory access.
uint64_t val = counter_.fetch_add(1, std::memory_order_relaxed);
return val % 1000 == 0;
}
private:
std::atomic<uint64_t> counter_{0};
};
// 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()
// Relaxed memory order since there is no dependent memory access.
g_accessed_subsampler.store(true, std::memory_order_relaxed);
#endif
return !!g_subsampler;
}
void InitializeCpuReductionExperiment() {
#if DCHECK_IS_ON()
// TSAN should generate an error if InitializeCpuReductionExperiment() races
// with IsRunningCpuReductionExperiment().
//
// Relaxed memory order since there is no dependent memory access.
DCHECK(!g_accessed_subsampler.load(std::memory_order_relaxed));
#endif
if (FeatureList::IsEnabled(kReduceCpuUtilization)) {
g_subsampler = new CpuReductionExperimentSubSampler();
}
}
bool ShouldLogHistogramForCpuReductionExperiment() {
if (!IsRunningCpuReductionExperiment())
return true;
return g_subsampler->ShouldLogHistograms();
}
} // namespace base