/*
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* Copyright (C) 2014 The Android Open Source Project
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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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*/
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#include <pthread.h>
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#include <semaphore.h>
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#include <stdatomic.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <benchmark/benchmark.h>
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#include "util.h"
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static void BM_semaphore_sem_getvalue(benchmark::State& state) {
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sem_t semaphore;
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sem_init(&semaphore, 1, 1);
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while (state.KeepRunning()) {
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int dummy;
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sem_getvalue(&semaphore, &dummy);
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}
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}
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BIONIC_BENCHMARK(BM_semaphore_sem_getvalue);
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static void BM_semaphore_sem_wait_sem_post(benchmark::State& state) {
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sem_t semaphore;
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sem_init(&semaphore, 1, 1);
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while (state.KeepRunning()) {
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sem_wait(&semaphore);
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sem_post(&semaphore);
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}
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}
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BIONIC_BENCHMARK(BM_semaphore_sem_wait_sem_post);
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// This test reports the overhead of the underlying futex wake syscall on
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// the producer. It does not report the overhead from issuing the wake to the
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// point where the posted consumer thread wakes up. It suffers from
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// clock_gettime syscall overhead. Lock the CPU speed for consistent results
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// as we may not reach >50% cpu utilization.
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//
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// We will run a background thread that catches the sem_post wakeup and
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// loops immediately returning back to sleep in sem_wait for the next one. This
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// thread is run with policy SCHED_OTHER (normal policy), a middle policy.
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//
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// The primary thread will run at SCHED_IDLE (lowest priority policy) when
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// monitoring the background thread to detect when it hits sem_wait sleep. It
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// will do so with no clock running. Once we are ready, we will switch to
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// SCHED_FIFO (highest priority policy) to time the act of running sem_post
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// with the benchmark clock running. This ensures nothing else in the system
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// can preempt our timed activity, including the background thread. We are
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// also protected with the scheduling policy of letting a process hit a
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// resource limit rather than get hit with a context switch.
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//
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// The background thread will start executing either on another CPU, or
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// after we back down from SCHED_FIFO, but certainly not in the context of
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// the timing of the sem_post.
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static atomic_int BM_semaphore_sem_post_running;
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static void* BM_semaphore_sem_post_start_thread(void* arg) {
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sem_t* semaphore = reinterpret_cast<sem_t*>(arg);
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while ((BM_semaphore_sem_post_running > 0) && !sem_wait(semaphore)) {
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}
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BM_semaphore_sem_post_running = -1;
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return nullptr;
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}
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class SemaphoreFixture : public benchmark::Fixture {
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public:
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void SetUp(const benchmark::State&) override {
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sem_init(&semaphore, 0, 0);
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pthread_attr_t attr;
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pthread_attr_init(&attr);
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memset(¶m, 0, sizeof(param));
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pthread_attr_setschedparam(&attr, ¶m);
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pthread_attr_setschedpolicy(&attr, SCHED_OTHER);
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pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
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pthread_t pthread;
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pthread_create(&pthread, &attr, BM_semaphore_sem_post_start_thread, &semaphore);
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pthread_attr_destroy(&attr);
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sched_setscheduler(0, SCHED_IDLE, ¶m);
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BM_semaphore_sem_post_running = 1;
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setup = true;
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}
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~SemaphoreFixture() override {
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if (setup) {
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// Only do this if the test was actually run.
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sched_setscheduler(0, SCHED_OTHER, ¶m);
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if (BM_semaphore_sem_post_running > 0) {
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BM_semaphore_sem_post_running = 0;
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}
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do {
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sem_post(&semaphore);
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sched_yield();
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} while (BM_semaphore_sem_post_running != -1);
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}
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}
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sem_t semaphore;
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sched_param param;
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bool setup = false;
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};
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// This is commented out because dynamic benchmark registering doesn't currently support fixtures.
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// Uncomment it and recompile to run this benchmark on every run.
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/* BENCHMARK_F(SemaphoreFixture, semaphore_sem_post)(benchmark::State& state) {
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while (state.KeepRunning()) {
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state.PauseTiming();
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int trys = 3, dummy = 0;
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do {
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if (BM_semaphore_sem_post_running < 0) {
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sched_setscheduler(0, SCHED_OTHER, ¶m);
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fprintf(stderr, "BM_semaphore_sem_post: start_thread died unexpectedly\n");
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abort();
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}
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sched_yield();
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sem_getvalue(&semaphore, &dummy);
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if (dummy < 0) { // POSIX.1-2001 possibility 1
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break;
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}
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if (dummy == 0) { // POSIX.1-2001 possibility 2
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--trys;
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}
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} while (trys);
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param.sched_priority = 1;
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sched_setscheduler(0, SCHED_FIFO, ¶m);
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state.ResumeTiming();
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sem_post(&semaphore);
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param.sched_priority = 0;
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sched_setscheduler(0, SCHED_IDLE, ¶m);
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}
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}*/
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