tools/perf/bench/futex-wake.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
   4  *
   5  * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
   6  *
   7  * This program is particularly useful to measure the latency of nthread wakeups
   8  * in non-error situations:  all waiters are queued and all wake calls wakeup
   9  * one or more tasks, and thus the waitqueue is never empty.
  10  */
  11
  12 /* For the CLR_() macros */
  13 #include <string.h>
  14 #include <pthread.h>
  15
  16 #include <signal.h>
  17 #include "../util/mutex.h"
  18 #include "../util/stat.h"
  19 #include <subcmd/parse-options.h>
  20 #include <linux/compiler.h>
  21 #include <linux/kernel.h>
  22 #include <linux/time64.h>
  23 #include <errno.h>
  24 #include <perf/cpumap.h>
  25 #include "bench.h"
  26 #include "futex.h"
  27
  28 #include <err.h>
  29 #include <stdlib.h>
  30 #include <sys/time.h>
  31 #include <sys/mman.h>
  32
  33 /* all threads will block on the same futex */
  34 static u_int32_t futex1 = 0;
  35
  36 static pthread_t *worker;
  37 static bool done = false;
  38 static struct mutex thread_lock;
  39 static struct cond thread_parent, thread_worker;
  40 static struct stats waketime_stats, wakeup_stats;
  41 static unsigned int threads_starting;
  42 static int futex_flag = 0;
  43
  44 static struct bench_futex_parameters params = {
  45         /*
  46          * How many wakeups to do at a time.
  47          * Default to 1 in order to make the kernel work more.
  48          */
  49         .nwakes  = 1,
  50 };
  51
  52 static const struct option options[] = {
  53         OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
  54         OPT_UINTEGER('w', "nwakes",  &params.nwakes, "Specify amount of threads to wake at once"),
  55         OPT_BOOLEAN( 's', "silent",  &params.silent, "Silent mode: do not display data/details"),
  56         OPT_BOOLEAN( 'S', "shared",  &params.fshared, "Use shared futexes instead of private ones"),
  57         OPT_BOOLEAN( 'm', "mlockall", &params.mlockall, "Lock all current and future memory"),
  58
  59         OPT_END()
  60 };
  61
  62 static const char * const bench_futex_wake_usage[] = {
  63         "perf bench futex wake <options>",
  64         NULL
  65 };
  66
  67 static void *workerfn(void *arg __maybe_unused)
  68 {
  69         mutex_lock(&thread_lock);
  70         threads_starting--;
  71         if (!threads_starting)
  72                 cond_signal(&thread_parent);
  73         cond_wait(&thread_worker, &thread_lock);
  74         mutex_unlock(&thread_lock);
  75
  76         while (1) {
  77                 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
  78                         break;
  79         }
  80
  81         pthread_exit(NULL);
  82         return NULL;
  83 }
  84
  85 static void print_summary(void)
  86 {
  87         double waketime_avg = avg_stats(&waketime_stats);
  88         double waketime_stddev = stddev_stats(&waketime_stats);
  89         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  90
  91         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  92                wakeup_avg,
  93                params.nthreads,
  94                waketime_avg / USEC_PER_MSEC,
  95                rel_stddev_stats(waketime_stddev, waketime_avg));
  96 }
  97
  98 static void block_threads(pthread_t *w, struct perf_cpu_map *cpu)
  99 {
 100         cpu_set_t *cpuset;
 101         unsigned int i;
 102         size_t size;
 103         int nrcpus = cpu__max_cpu().cpu;
 104         threads_starting = params.nthreads;
 105
 106         cpuset = CPU_ALLOC(nrcpus);
 107         BUG_ON(!cpuset);
 108         size = CPU_ALLOC_SIZE(nrcpus);
 109
 110         /* create and block all threads */
 111         for (i = 0; i < params.nthreads; i++) {
 112                 pthread_attr_t thread_attr;
 113
 114                 pthread_attr_init(&thread_attr);
 115                 CPU_ZERO_S(size, cpuset);
 116                 CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, size, cpuset);
 117
 118                 if (pthread_attr_setaffinity_np(&thread_attr, size, cpuset)) {
 119                         CPU_FREE(cpuset);
 120                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 121                 }
 122
 123                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) {
 124                         CPU_FREE(cpuset);
 125                         err(EXIT_FAILURE, "pthread_create");
 126                 }
 127                 pthread_attr_destroy(&thread_attr);
 128         }
 129         CPU_FREE(cpuset);
 130 }
 131
 132 static void toggle_done(int sig __maybe_unused,
 133                         siginfo_t *info __maybe_unused,
 134                         void *uc __maybe_unused)
 135 {
 136         done = true;
 137 }
 138
 139 int bench_futex_wake(int argc, const char **argv)
 140 {
 141         int ret = 0;
 142         unsigned int i, j;
 143         struct sigaction act;
 144         struct perf_cpu_map *cpu;
 145
 146         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 147         if (argc) {
 148                 usage_with_options(bench_futex_wake_usage, options);
 149                 exit(EXIT_FAILURE);
 150         }
 151
 152         cpu = perf_cpu_map__new_online_cpus();
 153         if (!cpu)
 154                 err(EXIT_FAILURE, "calloc");
 155
 156         memset(&act, 0, sizeof(act));
 157         sigfillset(&act.sa_mask);
 158         act.sa_sigaction = toggle_done;
 159         sigaction(SIGINT, &act, NULL);
 160
 161         if (params.mlockall) {
 162                 if (mlockall(MCL_CURRENT | MCL_FUTURE))
 163                         err(EXIT_FAILURE, "mlockall");
 164         }
 165
 166         if (!params.nthreads)
 167                 params.nthreads = perf_cpu_map__nr(cpu);
 168
 169         worker = calloc(params.nthreads, sizeof(*worker));
 170         if (!worker)
 171                 err(EXIT_FAILURE, "calloc");
 172
 173         if (!params.fshared)
 174                 futex_flag = FUTEX_PRIVATE_FLAG;
 175
 176         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
 177                "waking up %d at a time.\n\n",
 178                getpid(), params.nthreads, params.fshared ? "shared":"private",
 179                &futex1, params.nwakes);
 180
 181         init_stats(&wakeup_stats);
 182         init_stats(&waketime_stats);
 183         mutex_init(&thread_lock);
 184         cond_init(&thread_parent);
 185         cond_init(&thread_worker);
 186
 187         for (j = 0; j < bench_repeat && !done; j++) {
 188                 unsigned int nwoken = 0;
 189                 struct timeval start, end, runtime;
 190
 191                 /* create, launch & block all threads */
 192                 block_threads(worker, cpu);
 193
 194                 /* make sure all threads are already blocked */
 195                 mutex_lock(&thread_lock);
 196                 while (threads_starting)
 197                         cond_wait(&thread_parent, &thread_lock);
 198                 cond_broadcast(&thread_worker);
 199                 mutex_unlock(&thread_lock);
 200
 201                 usleep(100000);
 202
 203                 /* Ok, all threads are patiently blocked, start waking folks up */
 204                 gettimeofday(&start, NULL);
 205                 while (nwoken != params.nthreads)
 206                         nwoken += futex_wake(&futex1,
 207                                              params.nwakes, futex_flag);
 208                 gettimeofday(&end, NULL);
 209                 timersub(&end, &start, &runtime);
 210
 211                 update_stats(&wakeup_stats, nwoken);
 212                 update_stats(&waketime_stats, runtime.tv_usec);
 213
 214                 if (!params.silent) {
 215                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 216                                j + 1, nwoken, params.nthreads,
 217                                runtime.tv_usec / (double)USEC_PER_MSEC);
 218                 }
 219
 220                 for (i = 0; i < params.nthreads; i++) {
 221                         ret = pthread_join(worker[i], NULL);
 222                         if (ret)
 223                                 err(EXIT_FAILURE, "pthread_join");
 224                 }
 225
 226         }
 227
 228         /* cleanup & report results */
 229         cond_destroy(&thread_parent);
 230         cond_destroy(&thread_worker);
 231         mutex_destroy(&thread_lock);
 232
 233         print_summary();
 234
 235         free(worker);
 236         perf_cpu_map__put(cpu);
 237         return ret;
 238 }