tools/perf/bench/futex-requeue.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
   4  *
   5  * futex-requeue: Block a bunch of threads on futex1 and requeue them
   6  *                on futex2, N at a time.
   7  *
   8  * This program is particularly useful to measure the latency of nthread
   9  * requeues without waking up any tasks (in the non-pi case) -- thus
  10  * mimicking a regular futex_wait.
  11  */
  12
  13 /* For the CLR_() macros */
  14 #include <string.h>
  15 #include <pthread.h>
  16
  17 #include <signal.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 static u_int32_t futex1 = 0, futex2 = 0;
  34
  35 static pthread_t *worker;
  36 static bool done = false;
  37 static pthread_mutex_t thread_lock;
  38 static pthread_cond_t thread_parent, thread_worker;
  39 static struct stats requeuetime_stats, requeued_stats;
  40 static unsigned int threads_starting;
  41 static int futex_flag = 0;
  42
  43 static struct bench_futex_parameters params = {
  44         /*
  45          * How many tasks to requeue at a time.
  46          * Default to 1 in order to make the kernel work more.
  47          */
  48         .nrequeue = 1,
  49 };
  50
  51 static const struct option options[] = {
  52         OPT_UINTEGER('t', "threads",  &params.nthreads, "Specify amount of threads"),
  53         OPT_UINTEGER('q', "nrequeue", &params.nrequeue, "Specify amount of threads to requeue at once"),
  54         OPT_BOOLEAN( 's', "silent",   &params.silent, "Silent mode: do not display data/details"),
  55         OPT_BOOLEAN( 'S', "shared",   &params.fshared, "Use shared futexes instead of private ones"),
  56         OPT_BOOLEAN( 'm', "mlockall", &params.mlockall, "Lock all current and future memory"),
  57         OPT_BOOLEAN( 'B', "broadcast", &params.broadcast, "Requeue all threads at once"),
  58         OPT_BOOLEAN( 'p', "pi", &params.pi, "Use PI-aware variants of FUTEX_CMP_REQUEUE"),
  59
  60         OPT_END()
  61 };
  62
  63 static const char * const bench_futex_requeue_usage[] = {
  64         "perf bench futex requeue <options>",
  65         NULL
  66 };
  67
  68 static void print_summary(void)
  69 {
  70         double requeuetime_avg = avg_stats(&requeuetime_stats);
  71         double requeuetime_stddev = stddev_stats(&requeuetime_stats);
  72         unsigned int requeued_avg = avg_stats(&requeued_stats);
  73
  74         printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
  75                requeued_avg,
  76                params.nthreads,
  77                requeuetime_avg / USEC_PER_MSEC,
  78                rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
  79 }
  80
  81 static void *workerfn(void *arg __maybe_unused)
  82 {
  83         int ret;
  84
  85         pthread_mutex_lock(&thread_lock);
  86         threads_starting--;
  87         if (!threads_starting)
  88                 pthread_cond_signal(&thread_parent);
  89         pthread_cond_wait(&thread_worker, &thread_lock);
  90         pthread_mutex_unlock(&thread_lock);
  91
  92         while (1) {
  93                 if (!params.pi) {
  94                         ret = futex_wait(&futex1, 0, NULL, futex_flag);
  95                         if (!ret)
  96                                 break;
  97
  98                         if (ret && errno != EAGAIN) {
  99                                 if (!params.silent)
 100                                         warnx("futex_wait");
 101                                 break;
 102                         }
 103                 } else {
 104                         ret = futex_wait_requeue_pi(&futex1, 0, &futex2,
 105                                                     NULL, futex_flag);
 106                         if (!ret) {
 107                                 /* got the lock at futex2 */
 108                                 futex_unlock_pi(&futex2, futex_flag);
 109                                 break;
 110                         }
 111
 112                         if (ret && errno != EAGAIN) {
 113                                 if (!params.silent)
 114                                         warnx("futex_wait_requeue_pi");
 115                                 break;
 116                         }
 117                 }
 118         }
 119
 120         return NULL;
 121 }
 122
 123 static void block_threads(pthread_t *w,
 124                           pthread_attr_t thread_attr, struct perf_cpu_map *cpu)
 125 {
 126         cpu_set_t cpuset;
 127         unsigned int i;
 128
 129         threads_starting = params.nthreads;
 130
 131         /* create and block all threads */
 132         for (i = 0; i < params.nthreads; i++) {
 133                 CPU_ZERO(&cpuset);
 134                 CPU_SET(cpu->map[i % cpu->nr], &cpuset);
 135
 136                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
 137                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 138
 139                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 140                         err(EXIT_FAILURE, "pthread_create");
 141         }
 142 }
 143
 144 static void toggle_done(int sig __maybe_unused,
 145                         siginfo_t *info __maybe_unused,
 146                         void *uc __maybe_unused)
 147 {
 148         done = true;
 149 }
 150
 151 int bench_futex_requeue(int argc, const char **argv)
 152 {
 153         int ret = 0;
 154         unsigned int i, j;
 155         struct sigaction act;
 156         pthread_attr_t thread_attr;
 157         struct perf_cpu_map *cpu;
 158
 159         argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
 160         if (argc)
 161                 goto err;
 162
 163         cpu = perf_cpu_map__new(NULL);
 164         if (!cpu)
 165                 err(EXIT_FAILURE, "cpu_map__new");
 166
 167         memset(&act, 0, sizeof(act));
 168         sigfillset(&act.sa_mask);
 169         act.sa_sigaction = toggle_done;
 170         sigaction(SIGINT, &act, NULL);
 171
 172         if (params.mlockall) {
 173                 if (mlockall(MCL_CURRENT | MCL_FUTURE))
 174                         err(EXIT_FAILURE, "mlockall");
 175         }
 176
 177         if (!params.nthreads)
 178                 params.nthreads = cpu->nr;
 179
 180         worker = calloc(params.nthreads, sizeof(*worker));
 181         if (!worker)
 182                 err(EXIT_FAILURE, "calloc");
 183
 184         if (!params.fshared)
 185                 futex_flag = FUTEX_PRIVATE_FLAG;
 186
 187         if (params.nrequeue > params.nthreads)
 188                 params.nrequeue = params.nthreads;
 189
 190         if (params.broadcast)
 191                 params.nrequeue = params.nthreads;
 192
 193         printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %s%p), "
 194                "%d at a time.\n\n",  getpid(), params.nthreads,
 195                params.fshared ? "shared":"private", &futex1,
 196                params.pi ? "PI ": "", &futex2, params.nrequeue);
 197
 198         init_stats(&requeued_stats);
 199         init_stats(&requeuetime_stats);
 200         pthread_attr_init(&thread_attr);
 201         pthread_mutex_init(&thread_lock, NULL);
 202         pthread_cond_init(&thread_parent, NULL);
 203         pthread_cond_init(&thread_worker, NULL);
 204
 205         for (j = 0; j < bench_repeat && !done; j++) {
 206                 unsigned int nrequeued = 0, wakeups = 0;
 207                 struct timeval start, end, runtime;
 208
 209                 /* create, launch & block all threads */
 210                 block_threads(worker, thread_attr, cpu);
 211
 212                 /* make sure all threads are already blocked */
 213                 pthread_mutex_lock(&thread_lock);
 214                 while (threads_starting)
 215                         pthread_cond_wait(&thread_parent, &thread_lock);
 216                 pthread_cond_broadcast(&thread_worker);
 217                 pthread_mutex_unlock(&thread_lock);
 218
 219                 usleep(100000);
 220
 221                 /* Ok, all threads are patiently blocked, start requeueing */
 222                 gettimeofday(&start, NULL);
 223                 while (nrequeued < params.nthreads) {
 224                         int r;
 225
 226                         /*
 227                          * For the regular non-pi case, do not wakeup any tasks
 228                          * blocked on futex1, allowing us to really measure
 229                          * futex_wait functionality. For the PI case the first
 230                          * waiter is always awoken.
 231                          */
 232                         if (!params.pi) {
 233                                 r = futex_cmp_requeue(&futex1, 0, &futex2, 0,
 234                                                       params.nrequeue,
 235                                                       futex_flag);
 236                         } else {
 237                                 r = futex_cmp_requeue_pi(&futex1, 0, &futex2,
 238                                                          params.nrequeue,
 239                                                          futex_flag);
 240                                 wakeups++; /* assume no error */
 241                         }
 242
 243                         if (r < 0)
 244                                 err(EXIT_FAILURE, "couldn't requeue from %p to %p",
 245                                     &futex1, &futex2);
 246
 247                         nrequeued += r;
 248                 }
 249
 250                 gettimeofday(&end, NULL);
 251                 timersub(&end, &start, &runtime);
 252
 253                 update_stats(&requeued_stats, nrequeued);
 254                 update_stats(&requeuetime_stats, runtime.tv_usec);
 255
 256                 if (!params.silent) {
 257                         if (!params.pi)
 258                                 printf("[Run %d]: Requeued %d of %d threads in "
 259                                        "%.4f ms\n", j + 1, nrequeued,
 260                                        params.nthreads,
 261                                        runtime.tv_usec / (double)USEC_PER_MSEC);
 262                         else {
 263                                 nrequeued -= wakeups;
 264                                 printf("[Run %d]: Awoke and Requeued (%d+%d) of "
 265                                        "%d threads in %.4f ms\n",
 266                                        j + 1, wakeups, nrequeued,
 267                                        params.nthreads,
 268                                        runtime.tv_usec / (double)USEC_PER_MSEC);
 269                         }
 270
 271                 }
 272
 273                 if (!params.pi) {
 274                         /* everybody should be blocked on futex2, wake'em up */
 275                         nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
 276                         if (params.nthreads != nrequeued)
 277                                 warnx("couldn't wakeup all tasks (%d/%d)",
 278                                       nrequeued, params.nthreads);
 279                 }
 280
 281                 for (i = 0; i < params.nthreads; i++) {
 282                         ret = pthread_join(worker[i], NULL);
 283                         if (ret)
 284                                 err(EXIT_FAILURE, "pthread_join");
 285                 }
 286         }
 287
 288         /* cleanup & report results */
 289         pthread_cond_destroy(&thread_parent);
 290         pthread_cond_destroy(&thread_worker);
 291         pthread_mutex_destroy(&thread_lock);
 292         pthread_attr_destroy(&thread_attr);
 293
 294         print_summary();
 295
 296         free(worker);
 297         return ret;
 298 err:
 299         usage_with_options(bench_futex_requeue_usage, options);
 300         exit(EXIT_FAILURE);
 301 }