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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #include <pthread.h>
     18 #include <semaphore.h>
     19 #include <stdatomic.h>
     20 #include <stdio.h>
     21 
     22 #include <benchmark/Benchmark.h>
     23 
     24 BENCHMARK_NO_ARG(BM_semaphore_sem_getvalue);
     25 void BM_semaphore_sem_getvalue::Run(int iters) {
     26   StopBenchmarkTiming();
     27   sem_t semaphore;
     28   sem_init(&semaphore, 1, 1);
     29   StartBenchmarkTiming();
     30 
     31   for (int i = 0; i < iters; ++i) {
     32     int dummy;
     33     sem_getvalue(&semaphore, &dummy);
     34   }
     35 
     36   StopBenchmarkTiming();
     37 }
     38 
     39 BENCHMARK_NO_ARG(BM_semaphore_sem_wait_sem_post);
     40 void BM_semaphore_sem_wait_sem_post::Run(int iters) {
     41   StopBenchmarkTiming();
     42   sem_t semaphore;
     43   sem_init(&semaphore, 1, 1);
     44   StartBenchmarkTiming();
     45 
     46   for (int i = 0; i < iters; ++i) {
     47     sem_wait(&semaphore);
     48     sem_post(&semaphore);
     49   }
     50 
     51   StopBenchmarkTiming();
     52 }
     53 
     54 /*
     55  *    This test reports the overhead of the underlying futex wake syscall on
     56  * the producer. It does not report the overhead from issuing the wake to the
     57  * point where the posted consumer thread wakes up. It suffers from
     58  * clock_gettime syscall overhead. Lock the CPU speed for consistent results
     59  * as we may not reach >50% cpu utilization.
     60  *
     61  *    We will run a background thread that catches the sem_post wakeup and
     62  * loops immediately returning back to sleep in sem_wait for the next one. This
     63  * thread is run with policy SCHED_OTHER (normal policy), a middle policy.
     64  *
     65  *    The primary thread will run at SCHED_IDLE (lowest priority policy) when
     66  * monitoring the background thread to detect when it hits sem_wait sleep. It
     67  * will do so with no clock running. Once we are ready, we will switch to
     68  * SCHED_FIFO (highest priority policy) to time the act of running sem_post
     69  * with the benchmark clock running. This ensures nothing else in the system
     70  * can preempt our timed activity, including the background thread. We are
     71  * also protected with the scheduling policy of letting a process hit a
     72  * resource limit rather than get hit with a context switch.
     73  *
     74  *    The background thread will start executing either on another CPU, or
     75  * after we back down from SCHED_FIFO, but certainly not in the context of
     76  * the timing of the sem_post.
     77  */
     78 static atomic_int BM_semaphore_sem_post_running;
     79 
     80 static void *BM_semaphore_sem_post_start_thread(void *obj) {
     81     sem_t *semaphore = reinterpret_cast<sem_t *>(obj);
     82 
     83     while ((BM_semaphore_sem_post_running > 0) && !sem_wait(semaphore)) {
     84         ;
     85     }
     86     BM_semaphore_sem_post_running = -1;
     87     return NULL;
     88 }
     89 
     90 BENCHMARK_NO_ARG(BM_semaphore_sem_post);
     91 void BM_semaphore_sem_post::Run(int iters) {
     92   StopBenchmarkTiming();
     93 
     94   sem_t semaphore;
     95   sem_init(&semaphore, 0, 0);
     96 
     97   pthread_attr_t attr;
     98   pthread_attr_init(&attr);
     99   BM_semaphore_sem_post_running = 1;
    100   struct sched_param param = { 0, };
    101   pthread_attr_setschedparam(&attr, &param);
    102   pthread_attr_setschedpolicy(&attr, SCHED_OTHER);
    103   pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
    104   pthread_t pthread;
    105   pthread_create(&pthread, &attr, BM_semaphore_sem_post_start_thread, &semaphore);
    106   pthread_attr_destroy(&attr);
    107 
    108   sched_setscheduler((pid_t)0, SCHED_IDLE, &param);
    109   for (int i = 0; i < iters; ++i) {
    110     int trys = 3, dummy = 0;
    111     do {
    112       if (BM_semaphore_sem_post_running < 0) {
    113         sched_setscheduler((pid_t)0, SCHED_OTHER, &param);
    114         fprintf(stderr, "BM_semaphore_sem_post: start_thread died unexpectedly\n");
    115         return;
    116       }
    117       sched_yield();
    118       sem_getvalue(&semaphore, &dummy);
    119       if (dummy < 0) {  // POSIX.1-2001 possibility 1
    120         break;
    121       }
    122       if (dummy == 0) { // POSIX.1-2001 possibility 2
    123         --trys;
    124       }
    125     } while (trys);
    126     param.sched_priority = 1;
    127     sched_setscheduler((pid_t)0, SCHED_FIFO, &param);
    128     StartBenchmarkTiming();
    129     sem_post(&semaphore);
    130     StopBenchmarkTiming(); // Remember to subtract clock syscall overhead
    131     param.sched_priority = 0;
    132     sched_setscheduler((pid_t)0, SCHED_IDLE, &param);
    133   }
    134   sched_setscheduler((pid_t)0, SCHED_OTHER, &param);
    135 
    136   if (BM_semaphore_sem_post_running > 0) {
    137     BM_semaphore_sem_post_running = 0;
    138   }
    139   do {
    140     sem_post(&semaphore);
    141     sched_yield();
    142   } while (!BM_semaphore_sem_post_running);
    143 }
    144