tools/perf/bench/futex-wake-parallel.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2015 Davidlohr Bueso.
   4  *
   5  * Block a bunch of threads and let parallel waker threads wakeup an
   6  * equal amount of them. The program output reflects the avg latency
   7  * for each individual thread to service its share of work. Ultimately
   8  * it can be used to measure futex_wake() changes.
   9  */
  10 #include "bench.h"
  11 #include <linux/compiler.h>
  12 #include "../util/debug.h"
  13
  14 #ifndef HAVE_PTHREAD_BARRIER
  15 int bench_futex_wake_parallel(int argc __maybe_unused, const char **argv __maybe_unused)
  16 {
  17         pr_err("%s: pthread_barrier_t unavailable, disabling this test...\n", __func__);
  18         return 0;
  19 }
  20 #else /* HAVE_PTHREAD_BARRIER */
  21 /* For the CLR_() macros */
  22 #include <string.h>
  23 #include <pthread.h>
  24
  25 #include <signal.h>
  26 #include "../util/stat.h"
  27 #include <subcmd/parse-options.h>
  28 #include <linux/kernel.h>
  29 #include <linux/time64.h>
  30 #include <errno.h>
  31 #include "futex.h"
  32 #include "cpumap.h"
  33
  34 #include <err.h>
  35 #include <stdlib.h>
  36 #include <sys/time.h>
  37
  38 struct thread_data {
  39         pthread_t worker;
  40         unsigned int nwoken;
  41         struct timeval runtime;
  42 };
  43
  44 static unsigned int nwakes = 1;
  45
  46 /* all threads will block on the same futex -- hash bucket chaos ;) */
  47 static u_int32_t futex = 0;
  48
  49 static pthread_t *blocked_worker;
  50 static bool done = false, silent = false, fshared = false;
  51 static unsigned int nblocked_threads = 0, nwaking_threads = 0;
  52 static pthread_mutex_t thread_lock;
  53 static pthread_cond_t thread_parent, thread_worker;
  54 static pthread_barrier_t barrier;
  55 static struct stats waketime_stats, wakeup_stats;
  56 static unsigned int threads_starting;
  57 static int futex_flag = 0;
  58
  59 static const struct option options[] = {
  60         OPT_UINTEGER('t', "threads", &nblocked_threads, "Specify amount of threads"),
  61         OPT_UINTEGER('w', "nwakers", &nwaking_threads, "Specify amount of waking threads"),
  62         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  63         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
  64         OPT_END()
  65 };
  66
  67 static const char * const bench_futex_wake_parallel_usage[] = {
  68         "perf bench futex wake-parallel <options>",
  69         NULL
  70 };
  71
  72 static void *waking_workerfn(void *arg)
  73 {
  74         struct thread_data *waker = (struct thread_data *) arg;
  75         struct timeval start, end;
  76
  77         pthread_barrier_wait(&barrier);
  78
  79         gettimeofday(&start, NULL);
  80
  81         waker->nwoken = futex_wake(&futex, nwakes, futex_flag);
  82         if (waker->nwoken != nwakes)
  83                 warnx("couldn't wakeup all tasks (%d/%d)",
  84                       waker->nwoken, nwakes);
  85
  86         gettimeofday(&end, NULL);
  87         timersub(&end, &start, &waker->runtime);
  88
  89         pthread_exit(NULL);
  90         return NULL;
  91 }
  92
  93 static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
  94 {
  95         unsigned int i;
  96
  97         pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_JOINABLE);
  98
  99         pthread_barrier_init(&barrier, NULL, nwaking_threads + 1);
 100
 101         /* create and block all threads */
 102         for (i = 0; i < nwaking_threads; i++) {
 103                 /*
 104                  * Thread creation order will impact per-thread latency
 105                  * as it will affect the order to acquire the hb spinlock.
 106                  * For now let the scheduler decide.
 107                  */
 108                 if (pthread_create(&td[i].worker, &thread_attr,
 109                                    waking_workerfn, (void *)&td[i]))
 110                         err(EXIT_FAILURE, "pthread_create");
 111         }
 112
 113         pthread_barrier_wait(&barrier);
 114
 115         for (i = 0; i < nwaking_threads; i++)
 116                 if (pthread_join(td[i].worker, NULL))
 117                         err(EXIT_FAILURE, "pthread_join");
 118
 119         pthread_barrier_destroy(&barrier);
 120 }
 121
 122 static void *blocked_workerfn(void *arg __maybe_unused)
 123 {
 124         pthread_mutex_lock(&thread_lock);
 125         threads_starting--;
 126         if (!threads_starting)
 127                 pthread_cond_signal(&thread_parent);
 128         pthread_cond_wait(&thread_worker, &thread_lock);
 129         pthread_mutex_unlock(&thread_lock);
 130
 131         while (1) { /* handle spurious wakeups */
 132                 if (futex_wait(&futex, 0, NULL, futex_flag) != EINTR)
 133                         break;
 134         }
 135
 136         pthread_exit(NULL);
 137         return NULL;
 138 }
 139
 140 static void block_threads(pthread_t *w, pthread_attr_t thread_attr,
 141                           struct perf_cpu_map *cpu)
 142 {
 143         cpu_set_t cpuset;
 144         unsigned int i;
 145
 146         threads_starting = nblocked_threads;
 147
 148         /* create and block all threads */
 149         for (i = 0; i < nblocked_threads; i++) {
 150                 CPU_ZERO(&cpuset);
 151                 CPU_SET(cpu->map[i % cpu->nr], &cpuset);
 152
 153                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
 154                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 155
 156                 if (pthread_create(&w[i], &thread_attr, blocked_workerfn, NULL))
 157                         err(EXIT_FAILURE, "pthread_create");
 158         }
 159 }
 160
 161 static void print_run(struct thread_data *waking_worker, unsigned int run_num)
 162 {
 163         unsigned int i, wakeup_avg;
 164         double waketime_avg, waketime_stddev;
 165         struct stats __waketime_stats, __wakeup_stats;
 166
 167         init_stats(&__wakeup_stats);
 168         init_stats(&__waketime_stats);
 169
 170         for (i = 0; i < nwaking_threads; i++) {
 171                 update_stats(&__waketime_stats, waking_worker[i].runtime.tv_usec);
 172                 update_stats(&__wakeup_stats, waking_worker[i].nwoken);
 173         }
 174
 175         waketime_avg = avg_stats(&__waketime_stats);
 176         waketime_stddev = stddev_stats(&__waketime_stats);
 177         wakeup_avg = avg_stats(&__wakeup_stats);
 178
 179         printf("[Run %d]: Avg per-thread latency (waking %d/%d threads) "
 180                "in %.4f ms (+-%.2f%%)\n", run_num + 1, wakeup_avg,
 181                nblocked_threads, waketime_avg / USEC_PER_MSEC,
 182                rel_stddev_stats(waketime_stddev, waketime_avg));
 183 }
 184
 185 static void print_summary(void)
 186 {
 187         unsigned int wakeup_avg;
 188         double waketime_avg, waketime_stddev;
 189
 190         waketime_avg = avg_stats(&waketime_stats);
 191         waketime_stddev = stddev_stats(&waketime_stats);
 192         wakeup_avg = avg_stats(&wakeup_stats);
 193
 194         printf("Avg per-thread latency (waking %d/%d threads) in %.4f ms (+-%.2f%%)\n",
 195                wakeup_avg,
 196                nblocked_threads,
 197                waketime_avg / USEC_PER_MSEC,
 198                rel_stddev_stats(waketime_stddev, waketime_avg));
 199 }
 200
 201
 202 static void do_run_stats(struct thread_data *waking_worker)
 203 {
 204         unsigned int i;
 205
 206         for (i = 0; i < nwaking_threads; i++) {
 207                 update_stats(&waketime_stats, waking_worker[i].runtime.tv_usec);
 208                 update_stats(&wakeup_stats, waking_worker[i].nwoken);
 209         }
 210
 211 }
 212
 213 static void toggle_done(int sig __maybe_unused,
 214                         siginfo_t *info __maybe_unused,
 215                         void *uc __maybe_unused)
 216 {
 217         done = true;
 218 }
 219
 220 int bench_futex_wake_parallel(int argc, const char **argv)
 221 {
 222         int ret = 0;
 223         unsigned int i, j;
 224         struct sigaction act;
 225         pthread_attr_t thread_attr;
 226         struct thread_data *waking_worker;
 227         struct perf_cpu_map *cpu;
 228
 229         argc = parse_options(argc, argv, options,
 230                              bench_futex_wake_parallel_usage, 0);
 231         if (argc) {
 232                 usage_with_options(bench_futex_wake_parallel_usage, options);
 233                 exit(EXIT_FAILURE);
 234         }
 235
 236         sigfillset(&act.sa_mask);
 237         act.sa_sigaction = toggle_done;
 238         sigaction(SIGINT, &act, NULL);
 239
 240         cpu = perf_cpu_map__new(NULL);
 241         if (!cpu)
 242                 err(EXIT_FAILURE, "calloc");
 243
 244         if (!nblocked_threads)
 245                 nblocked_threads = cpu->nr;
 246
 247         /* some sanity checks */
 248         if (nwaking_threads > nblocked_threads || !nwaking_threads)
 249                 nwaking_threads = nblocked_threads;
 250
 251         if (nblocked_threads % nwaking_threads)
 252                 errx(EXIT_FAILURE, "Must be perfectly divisible");
 253         /*
 254          * Each thread will wakeup nwakes tasks in
 255          * a single futex_wait call.
 256          */
 257         nwakes = nblocked_threads/nwaking_threads;
 258
 259         blocked_worker = calloc(nblocked_threads, sizeof(*blocked_worker));
 260         if (!blocked_worker)
 261                 err(EXIT_FAILURE, "calloc");
 262
 263         if (!fshared)
 264                 futex_flag = FUTEX_PRIVATE_FLAG;
 265
 266         printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
 267                "futex %p), %d threads waking up %d at a time.\n\n",
 268                getpid(), nblocked_threads, fshared ? "shared":"private",
 269                &futex, nwaking_threads, nwakes);
 270
 271         init_stats(&wakeup_stats);
 272         init_stats(&waketime_stats);
 273
 274         pthread_attr_init(&thread_attr);
 275         pthread_mutex_init(&thread_lock, NULL);
 276         pthread_cond_init(&thread_parent, NULL);
 277         pthread_cond_init(&thread_worker, NULL);
 278
 279         for (j = 0; j < bench_repeat && !done; j++) {
 280                 waking_worker = calloc(nwaking_threads, sizeof(*waking_worker));
 281                 if (!waking_worker)
 282                         err(EXIT_FAILURE, "calloc");
 283
 284                 /* create, launch & block all threads */
 285                 block_threads(blocked_worker, thread_attr, cpu);
 286
 287                 /* make sure all threads are already blocked */
 288                 pthread_mutex_lock(&thread_lock);
 289                 while (threads_starting)
 290                         pthread_cond_wait(&thread_parent, &thread_lock);
 291                 pthread_cond_broadcast(&thread_worker);
 292                 pthread_mutex_unlock(&thread_lock);
 293
 294                 usleep(100000);
 295
 296                 /* Ok, all threads are patiently blocked, start waking folks up */
 297                 wakeup_threads(waking_worker, thread_attr);
 298
 299                 for (i = 0; i < nblocked_threads; i++) {
 300                         ret = pthread_join(blocked_worker[i], NULL);
 301                         if (ret)
 302                                 err(EXIT_FAILURE, "pthread_join");
 303                 }
 304
 305                 do_run_stats(waking_worker);
 306                 if (!silent)
 307                         print_run(waking_worker, j);
 308
 309                 free(waking_worker);
 310         }
 311
 312         /* cleanup & report results */
 313         pthread_cond_destroy(&thread_parent);
 314         pthread_cond_destroy(&thread_worker);
 315         pthread_mutex_destroy(&thread_lock);
 316         pthread_attr_destroy(&thread_attr);
 317
 318         print_summary();
 319
 320         free(blocked_worker);
 321         return ret;
 322 }
 323 #endif /* HAVE_PTHREAD_BARRIER */