linux/tools/perf/bench/futex-wake-parallel.c
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   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
  15int 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 <perf/cpumap.h>
  33
  34#include <err.h>
  35#include <stdlib.h>
  36#include <sys/time.h>
  37
  38struct thread_data {
  39        pthread_t worker;
  40        unsigned int nwoken;
  41        struct timeval runtime;
  42};
  43
  44static unsigned int nwakes = 1;
  45
  46/* all threads will block on the same futex -- hash bucket chaos ;) */
  47static u_int32_t futex = 0;
  48
  49static pthread_t *blocked_worker;
  50static bool done = false, silent = false, fshared = false;
  51static unsigned int nblocked_threads = 0, nwaking_threads = 0;
  52static pthread_mutex_t thread_lock;
  53static pthread_cond_t thread_parent, thread_worker;
  54static pthread_barrier_t barrier;
  55static struct stats waketime_stats, wakeup_stats;
  56static unsigned int threads_starting;
  57static int futex_flag = 0;
  58
  59static 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
  67static const char * const bench_futex_wake_parallel_usage[] = {
  68        "perf bench futex wake-parallel <options>",
  69        NULL
  70};
  71
  72static 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
  93static 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
 122static 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
 140static 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
 161static 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
 185static 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
 202static 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
 213static void toggle_done(int sig __maybe_unused,
 214                        siginfo_t *info __maybe_unused,
 215                        void *uc __maybe_unused)
 216{
 217        done = true;
 218}
 219
 220int 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        memset(&act, 0, sizeof(act));
 237        sigfillset(&act.sa_mask);
 238        act.sa_sigaction = toggle_done;
 239        sigaction(SIGINT, &act, NULL);
 240
 241        cpu = perf_cpu_map__new(NULL);
 242        if (!cpu)
 243                err(EXIT_FAILURE, "calloc");
 244
 245        if (!nblocked_threads)
 246                nblocked_threads = cpu->nr;
 247
 248        /* some sanity checks */
 249        if (nwaking_threads > nblocked_threads || !nwaking_threads)
 250                nwaking_threads = nblocked_threads;
 251
 252        if (nblocked_threads % nwaking_threads)
 253                errx(EXIT_FAILURE, "Must be perfectly divisible");
 254        /*
 255         * Each thread will wakeup nwakes tasks in
 256         * a single futex_wait call.
 257         */
 258        nwakes = nblocked_threads/nwaking_threads;
 259
 260        blocked_worker = calloc(nblocked_threads, sizeof(*blocked_worker));
 261        if (!blocked_worker)
 262                err(EXIT_FAILURE, "calloc");
 263
 264        if (!fshared)
 265                futex_flag = FUTEX_PRIVATE_FLAG;
 266
 267        printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
 268               "futex %p), %d threads waking up %d at a time.\n\n",
 269               getpid(), nblocked_threads, fshared ? "shared":"private",
 270               &futex, nwaking_threads, nwakes);
 271
 272        init_stats(&wakeup_stats);
 273        init_stats(&waketime_stats);
 274
 275        pthread_attr_init(&thread_attr);
 276        pthread_mutex_init(&thread_lock, NULL);
 277        pthread_cond_init(&thread_parent, NULL);
 278        pthread_cond_init(&thread_worker, NULL);
 279
 280        for (j = 0; j < bench_repeat && !done; j++) {
 281                waking_worker = calloc(nwaking_threads, sizeof(*waking_worker));
 282                if (!waking_worker)
 283                        err(EXIT_FAILURE, "calloc");
 284
 285                /* create, launch & block all threads */
 286                block_threads(blocked_worker, thread_attr, cpu);
 287
 288                /* make sure all threads are already blocked */
 289                pthread_mutex_lock(&thread_lock);
 290                while (threads_starting)
 291                        pthread_cond_wait(&thread_parent, &thread_lock);
 292                pthread_cond_broadcast(&thread_worker);
 293                pthread_mutex_unlock(&thread_lock);
 294
 295                usleep(100000);
 296
 297                /* Ok, all threads are patiently blocked, start waking folks up */
 298                wakeup_threads(waking_worker, thread_attr);
 299
 300                for (i = 0; i < nblocked_threads; i++) {
 301                        ret = pthread_join(blocked_worker[i], NULL);
 302                        if (ret)
 303                                err(EXIT_FAILURE, "pthread_join");
 304                }
 305
 306                do_run_stats(waking_worker);
 307                if (!silent)
 308                        print_run(waking_worker, j);
 309
 310                free(waking_worker);
 311        }
 312
 313        /* cleanup & report results */
 314        pthread_cond_destroy(&thread_parent);
 315        pthread_cond_destroy(&thread_worker);
 316        pthread_mutex_destroy(&thread_lock);
 317        pthread_attr_destroy(&thread_attr);
 318
 319        print_summary();
 320
 321        free(blocked_worker);
 322        return ret;
 323}
 324#endif /* HAVE_PTHREAD_BARRIER */
 325
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