95 lines
2.8 KiB
C++
95 lines
2.8 KiB
C++
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// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include <vector>
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#include "benchmark/benchmark.h"
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#include "absl/base/internal/sysinfo.h"
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#include "absl/synchronization/blocking_counter.h"
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#include "absl/synchronization/internal/thread_pool.h"
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#include "absl/synchronization/mutex.h"
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namespace {
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// Measure the overhead of conditions on mutex release (when they must be
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// evaluated). Mutex has (some) support for equivalence classes allowing
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// Conditions with the same function/argument to potentially not be multiply
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// evaluated.
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//
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// num_classes==0 is used for the special case of every waiter being distinct.
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void BM_ConditionWaiters(benchmark::State& state) {
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int num_classes = state.range(0);
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int num_waiters = state.range(1);
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struct Helper {
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static void Waiter(absl::BlockingCounter* init, absl::Mutex* m, int* p) {
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init->DecrementCount();
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m->LockWhen(absl::Condition(
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static_cast<bool (*)(int*)>([](int* v) { return *v == 0; }), p));
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m->Unlock();
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}
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};
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if (num_classes == 0) {
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// No equivalence classes.
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num_classes = num_waiters;
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}
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absl::BlockingCounter init(num_waiters);
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absl::Mutex mu;
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std::vector<int> equivalence_classes(num_classes, 1);
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// Must be declared last to be destroyed first.
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absl::synchronization_internal::ThreadPool pool(num_waiters);
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for (int i = 0; i < num_waiters; i++) {
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// Mutex considers Conditions with the same function and argument
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// to be equivalent.
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pool.Schedule([&, i] {
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Helper::Waiter(&init, &mu, &equivalence_classes[i % num_classes]);
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});
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}
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init.Wait();
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for (auto _ : state) {
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mu.Lock();
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mu.Unlock(); // Each unlock requires Condition evaluation for our waiters.
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}
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mu.Lock();
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for (int i = 0; i < num_classes; i++) {
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equivalence_classes[i] = 0;
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}
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mu.Unlock();
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}
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#ifdef THREAD_SANITIZER
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// ThreadSanitizer can't handle 8192 threads.
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constexpr int kMaxConditionWaiters = 2048;
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#else
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constexpr int kMaxConditionWaiters = 8192;
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#endif
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BENCHMARK(BM_ConditionWaiters)->RangePair(0, 2, 1, kMaxConditionWaiters);
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void BM_ContendedMutex(benchmark::State& state) {
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static absl::Mutex* mu = new absl::Mutex;
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for (auto _ : state) {
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absl::MutexLock lock(mu);
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}
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}
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BENCHMARK(BM_ContendedMutex)->Threads(1);
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BENCHMARK(BM_ContendedMutex)->ThreadPerCpu();
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} // namespace
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