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

   1 /*
   2  * Copyright (C) 2015 Davidlohr Bueso.
   3  *
   4  * Block a bunch of threads and let parallel waker threads wakeup an
   5  * equal amount of them. The program output reflects the avg latency
   6  * for each individual thread to service its share of work. Ultimately
   7  * it can be used to measure futex_wake() changes.
   8  */
   9
  10 #include "../perf.h"
  11 #include "../util/util.h"
  12 #include "../util/stat.h"
  13 #include <subcmd/parse-options.h>
  14 #include "../util/header.h"
  15 #include "bench.h"
  16 #include "futex.h"
  17
  18 #include <err.h>
  19 #include <stdlib.h>
  20 #include <sys/time.h>
  21 #include <pthread.h>
  22
  23 struct thread_data {
  24         pthread_t worker;
  25         unsigned int nwoken;
  26         struct timeval runtime;
  27 };
  28
  29 static unsigned int nwakes = 1;
  30
  31 /* all threads will block on the same futex -- hash bucket chaos ;) */
  32 static u_int32_t futex = 0;
  33
  34 static pthread_t *blocked_worker;
  35 static bool done = false, silent = false, fshared = false;
  36 static unsigned int nblocked_threads = 0, nwaking_threads = 0;
  37 static pthread_mutex_t thread_lock;
  38 static pthread_cond_t thread_parent, thread_worker;
  39 static struct stats waketime_stats, wakeup_stats;
  40 static unsigned int ncpus, threads_starting;
  41 static int futex_flag = 0;
  42
  43 static const struct option options[] = {
  44         OPT_UINTEGER('t', "threads", &nblocked_threads, "Specify amount of threads"),
  45         OPT_UINTEGER('w', "nwakers", &nwaking_threads, "Specify amount of waking threads"),
  46         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  47         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
  48         OPT_END()
  49 };
  50
  51 static const char * const bench_futex_wake_parallel_usage[] = {
  52         "perf bench futex wake-parallel <options>",
  53         NULL
  54 };
  55
  56 static void *waking_workerfn(void *arg)
  57 {
  58         struct thread_data *waker = (struct thread_data *) arg;
  59         struct timeval start, end;
  60
  61         gettimeofday(&start, NULL);
  62
  63         waker->nwoken = futex_wake(&futex, nwakes, futex_flag);
  64         if (waker->nwoken != nwakes)
  65                 warnx("couldn't wakeup all tasks (%d/%d)",
  66                       waker->nwoken, nwakes);
  67
  68         gettimeofday(&end, NULL);
  69         timersub(&end, &start, &waker->runtime);
  70
  71         pthread_exit(NULL);
  72         return NULL;
  73 }
  74
  75 static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
  76 {
  77         unsigned int i;
  78
  79         pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_JOINABLE);
  80
  81         /* create and block all threads */
  82         for (i = 0; i < nwaking_threads; i++) {
  83                 /*
  84                  * Thread creation order will impact per-thread latency
  85                  * as it will affect the order to acquire the hb spinlock.
  86                  * For now let the scheduler decide.
  87                  */
  88                 if (pthread_create(&td[i].worker, &thread_attr,
  89                                    waking_workerfn, (void *)&td[i]))
  90                         err(EXIT_FAILURE, "pthread_create");
  91         }
  92
  93         for (i = 0; i < nwaking_threads; i++)
  94                 if (pthread_join(td[i].worker, NULL))
  95                         err(EXIT_FAILURE, "pthread_join");
  96 }
  97
  98 static void *blocked_workerfn(void *arg __maybe_unused)
  99 {
 100         pthread_mutex_lock(&thread_lock);
 101         threads_starting--;
 102         if (!threads_starting)
 103                 pthread_cond_signal(&thread_parent);
 104         pthread_cond_wait(&thread_worker, &thread_lock);
 105         pthread_mutex_unlock(&thread_lock);
 106
 107         while (1) { /* handle spurious wakeups */
 108                 if (futex_wait(&futex, 0, NULL, futex_flag) != EINTR)
 109                         break;
 110         }
 111
 112         pthread_exit(NULL);
 113         return NULL;
 114 }
 115
 116 static void block_threads(pthread_t *w, pthread_attr_t thread_attr)
 117 {
 118         cpu_set_t cpu;
 119         unsigned int i;
 120
 121         threads_starting = nblocked_threads;
 122
 123         /* create and block all threads */
 124         for (i = 0; i < nblocked_threads; i++) {
 125                 CPU_ZERO(&cpu);
 126                 CPU_SET(i % ncpus, &cpu);
 127
 128                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
 129                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 130
 131                 if (pthread_create(&w[i], &thread_attr, blocked_workerfn, NULL))
 132                         err(EXIT_FAILURE, "pthread_create");
 133         }
 134 }
 135
 136 static void print_run(struct thread_data *waking_worker, unsigned int run_num)
 137 {
 138         unsigned int i, wakeup_avg;
 139         double waketime_avg, waketime_stddev;
 140         struct stats __waketime_stats, __wakeup_stats;
 141
 142         init_stats(&__wakeup_stats);
 143         init_stats(&__waketime_stats);
 144
 145         for (i = 0; i < nwaking_threads; i++) {
 146                 update_stats(&__waketime_stats, waking_worker[i].runtime.tv_usec);
 147                 update_stats(&__wakeup_stats, waking_worker[i].nwoken);
 148         }
 149
 150         waketime_avg = avg_stats(&__waketime_stats);
 151         waketime_stddev = stddev_stats(&__waketime_stats);
 152         wakeup_avg = avg_stats(&__wakeup_stats);
 153
 154         printf("[Run %d]: Avg per-thread latency (waking %d/%d threads) "
 155                "in %.4f ms (+-%.2f%%)\n", run_num + 1, wakeup_avg,
 156                nblocked_threads, waketime_avg/1e3,
 157                rel_stddev_stats(waketime_stddev, waketime_avg));
 158 }
 159
 160 static void print_summary(void)
 161 {
 162         unsigned int wakeup_avg;
 163         double waketime_avg, waketime_stddev;
 164
 165         waketime_avg = avg_stats(&waketime_stats);
 166         waketime_stddev = stddev_stats(&waketime_stats);
 167         wakeup_avg = avg_stats(&wakeup_stats);
 168
 169         printf("Avg per-thread latency (waking %d/%d threads) in %.4f ms (+-%.2f%%)\n",
 170                wakeup_avg,
 171                nblocked_threads,
 172                waketime_avg/1e3,
 173                rel_stddev_stats(waketime_stddev, waketime_avg));
 174 }
 175
 176
 177 static void do_run_stats(struct thread_data *waking_worker)
 178 {
 179         unsigned int i;
 180
 181         for (i = 0; i < nwaking_threads; i++) {
 182                 update_stats(&waketime_stats, waking_worker[i].runtime.tv_usec);
 183                 update_stats(&wakeup_stats, waking_worker[i].nwoken);
 184         }
 185
 186 }
 187
 188 static void toggle_done(int sig __maybe_unused,
 189                         siginfo_t *info __maybe_unused,
 190                         void *uc __maybe_unused)
 191 {
 192         done = true;
 193 }
 194
 195 int bench_futex_wake_parallel(int argc, const char **argv,
 196                               const char *prefix __maybe_unused)
 197 {
 198         int ret = 0;
 199         unsigned int i, j;
 200         struct sigaction act;
 201         pthread_attr_t thread_attr;
 202         struct thread_data *waking_worker;
 203
 204         argc = parse_options(argc, argv, options,
 205                              bench_futex_wake_parallel_usage, 0);
 206         if (argc) {
 207                 usage_with_options(bench_futex_wake_parallel_usage, options);
 208                 exit(EXIT_FAILURE);
 209         }
 210
 211         sigfillset(&act.sa_mask);
 212         act.sa_sigaction = toggle_done;
 213         sigaction(SIGINT, &act, NULL);
 214
 215         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 216         if (!nblocked_threads)
 217                 nblocked_threads = ncpus;
 218
 219         /* some sanity checks */
 220         if (nwaking_threads > nblocked_threads || !nwaking_threads)
 221                 nwaking_threads = nblocked_threads;
 222
 223         if (nblocked_threads % nwaking_threads)
 224                 errx(EXIT_FAILURE, "Must be perfectly divisible");
 225         /*
 226          * Each thread will wakeup nwakes tasks in
 227          * a single futex_wait call.
 228          */
 229         nwakes = nblocked_threads/nwaking_threads;
 230
 231         blocked_worker = calloc(nblocked_threads, sizeof(*blocked_worker));
 232         if (!blocked_worker)
 233                 err(EXIT_FAILURE, "calloc");
 234
 235         if (!fshared)
 236                 futex_flag = FUTEX_PRIVATE_FLAG;
 237
 238         printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
 239                "futex %p), %d threads waking up %d at a time.\n\n",
 240                getpid(), nblocked_threads, fshared ? "shared":"private",
 241                &futex, nwaking_threads, nwakes);
 242
 243         init_stats(&wakeup_stats);
 244         init_stats(&waketime_stats);
 245
 246         pthread_attr_init(&thread_attr);
 247         pthread_mutex_init(&thread_lock, NULL);
 248         pthread_cond_init(&thread_parent, NULL);
 249         pthread_cond_init(&thread_worker, NULL);
 250
 251         for (j = 0; j < bench_repeat && !done; j++) {
 252                 waking_worker = calloc(nwaking_threads, sizeof(*waking_worker));
 253                 if (!waking_worker)
 254                         err(EXIT_FAILURE, "calloc");
 255
 256                 /* create, launch & block all threads */
 257                 block_threads(blocked_worker, thread_attr);
 258
 259                 /* make sure all threads are already blocked */
 260                 pthread_mutex_lock(&thread_lock);
 261                 while (threads_starting)
 262                         pthread_cond_wait(&thread_parent, &thread_lock);
 263                 pthread_cond_broadcast(&thread_worker);
 264                 pthread_mutex_unlock(&thread_lock);
 265
 266                 usleep(100000);
 267
 268                 /* Ok, all threads are patiently blocked, start waking folks up */
 269                 wakeup_threads(waking_worker, thread_attr);
 270
 271                 for (i = 0; i < nblocked_threads; i++) {
 272                         ret = pthread_join(blocked_worker[i], NULL);
 273                         if (ret)
 274                                 err(EXIT_FAILURE, "pthread_join");
 275                 }
 276
 277                 do_run_stats(waking_worker);
 278                 if (!silent)
 279                         print_run(waking_worker, j);
 280
 281                 free(waking_worker);
 282         }
 283
 284         /* cleanup & report results */
 285         pthread_cond_destroy(&thread_parent);
 286         pthread_cond_destroy(&thread_worker);
 287         pthread_mutex_destroy(&thread_lock);
 288         pthread_attr_destroy(&thread_attr);
 289
 290         print_summary();
 291
 292         free(blocked_worker);
 293         return ret;
 294 }