| // 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 |