[libcxx-commits] [libcxx] [libc++][test] add benchmarks for `std::atomic::wait` (PR #70571)
Louis Dionne via libcxx-commits
libcxx-commits at lists.llvm.org
Mon Nov 27 10:28:16 PST 2023
================
@@ -0,0 +1,163 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <atomic>
+#include <numeric>
+#include <thread>
+
+#include "benchmark/benchmark.h"
+#include "make_test_thread.h"
+
+#include <iostream>
+
+using namespace std::chrono_literals;
+
+void BM_atomic_wait_one_thread_one_atomic_wait(benchmark::State& state) {
+ std::atomic<std::uint64_t> a;
+ auto thread_func = [&](std::stop_token st) {
+ while (!st.stop_requested()) {
+ a.fetch_add(1, std::memory_order_relaxed);
+ a.notify_all();
+ }
+ };
+
+ std::uint64_t total_loop_test_param = state.range(0);
+
+ auto thread = support::make_test_jthread(thread_func);
+
+ for (auto _ : state) {
+ for (std::uint64_t i = 0; i < total_loop_test_param; ++i) {
+ auto old = a.load(std::memory_order_relaxed);
+ a.wait(old);
+ }
+ }
+}
+BENCHMARK(BM_atomic_wait_one_thread_one_atomic_wait)->RangeMultiplier(2)->Range(1 << 10, 1 << 24);
+
+void BM_atomic_wait_multi_thread_one_atomic_wait(benchmark::State& state) {
+ std::atomic<std::uint64_t> a;
+ auto notify_func = [&](std::stop_token st) {
+ while (!st.stop_requested()) {
+ a.fetch_add(1, std::memory_order_relaxed);
+ a.notify_all();
+ }
+ };
+
+ std::uint64_t total_loop_test_param = state.range(0);
+ constexpr auto num_waiting_threads = 15;
+ std::vector<std::jthread> wait_threads;
+ wait_threads.reserve(num_waiting_threads);
+
+ auto notify_thread = support::make_test_jthread(notify_func);
+
+ std::atomic<std::uint64_t> start_flag = 0;
+ std::atomic<std::uint64_t> done_count = 0;
+ auto wait_func = [&a, &start_flag, &done_count, total_loop_test_param](std::stop_token st) {
+ auto old_start = 0;
+ while (!st.stop_requested()) {
+ start_flag.wait(old_start);
+ old_start = start_flag.load();
+ for (std::uint64_t i = 0; i < total_loop_test_param; ++i) {
+ auto old = a.load(std::memory_order_relaxed);
+ a.wait(old);
+ }
+ done_count.fetch_add(1);
+ }
+ };
+
+ for (size_t i = 0; i < num_waiting_threads; ++i) {
+ wait_threads.emplace_back(support::make_test_jthread(wait_func));
+ }
+
+ for (auto _ : state) {
+ done_count = 0;
+ start_flag.fetch_add(1);
+ start_flag.notify_all();
+ while (done_count < num_waiting_threads) {
+ std::this_thread::yield();
+ }
+ }
+ for (auto& t : wait_threads) {
+ t.request_stop();
+ }
+ start_flag.fetch_add(1);
+ start_flag.notify_all();
+ for (auto& t : wait_threads) {
+ t.join();
+ }
+}
+BENCHMARK(BM_atomic_wait_multi_thread_one_atomic_wait)->RangeMultiplier(2)->Range(1 << 10, 1 << 20);
+
+// hardware_destructive_interference_size not implemented yet for clang
+// alignas 128 to cover the cases for x86 and apple arm to prevent false sharing
+// from the test itself
+struct alignas(128) Atomic {
+ std::atomic<std::uint64_t> at{0};
+};
----------------
ldionne wrote:
I think this was a temporary test, it probably shouldn't be in the base benchmark.
https://github.com/llvm/llvm-project/pull/70571
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