tools/perf/bench/futex-requeue.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2013  Davidlohr Bueso <[email protected]>
   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/mutex.h"
  19 #include "../util/stat.h"
  20 #include <subcmd/parse-options.h>
  21 #include <linux/compiler.h>
  22 #include <linux/kernel.h>
  23 #include <linux/time64.h>
  24 #include <errno.h>
  25 #include <perf/cpumap.h>
  26 #include "bench.h"
  27 #include "futex.h"
  28
  29 #include <err.h>
  30 #include <stdlib.h>
  31 #include <sys/time.h>
  32 #include <sys/mman.h>
  33
  34 static u_int32_t futex1 = 0, futex2 = 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 requeuetime_stats, requeued_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 tasks to requeue at a time.
  47          * Default to 1 in order to make the kernel work more.
  48          */
  49         .nrequeue = 1,
  50 };
  51
  52 static const struct option options[] = {
  53         OPT_UINTEGER('t', "threads",  &params.nthreads, "Specify amount of threads"),
  54         OPT_UINTEGER('q', "nrequeue", &params.nrequeue, "Specify amount of threads to requeue 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         OPT_BOOLEAN( 'B', "broadcast", &params.broadcast, "Requeue all threads at once"),
  59         OPT_BOOLEAN( 'p', "pi", &params.pi, "Use PI-aware variants of FUTEX_CMP_REQUEUE"),
  60
  61         OPT_END()
  62 };
  63
  64 static const char * const bench_futex_requeue_usage[] = {
  65         "perf bench futex requeue <options>",
  66         NULL
  67 };
  68
  69 static void print_summary(void)
  70 {
  71         double requeuetime_avg = avg_stats(&requeuetime_stats);
  72         double requeuetime_stddev = stddev_stats(&requeuetime_stats);
  73         unsigned int requeued_avg = avg_stats(&requeued_stats);
  74
  75         printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
  76                requeued_avg,
  77                params.nthreads,
  78                requeuetime_avg / USEC_PER_MSEC,
  79                rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
  80 }
  81
  82 static void *workerfn(void *arg __maybe_unused)
  83 {
  84         int ret;
  85
  86         mutex_lock(&thread_lock);
  87         threads_starting--;
  88         if (!threads_starting)
  89                 cond_signal(&thread_parent);
  90         cond_wait(&thread_worker, &thread_lock);
  91         mutex_unlock(&thread_lock);
  92
  93         while (1) {
  94                 if (!params.pi) {
  95                         ret = futex_wait(&futex1, 0, NULL, futex_flag);
  96                         if (!ret)
  97                                 break;
  98
  99                         if (ret && errno != EAGAIN) {
 100                                 if (!params.silent)
 101                                         warnx("futex_wait");
 102                                 break;
 103                         }
 104                 } else {
 105                         ret = futex_wait_requeue_pi(&futex1, 0, &futex2,
 106                                                     NULL, futex_flag);
 107                         if (!ret) {
 108                                 /* got the lock at futex2 */
 109                                 futex_unlock_pi(&futex2, futex_flag);
 110                                 break;
 111                         }
 112
 113                         if (ret && errno != EAGAIN) {
 114                                 if (!params.silent)
 115                                         warnx("futex_wait_requeue_pi");
 116                                 break;
 117                         }
 118                 }
 119         }
 120
 121         return NULL;
 122 }
 123
 124 static void block_threads(pthread_t *w,
 125                           pthread_attr_t thread_attr, struct perf_cpu_map *cpu)
 126 {
 127         cpu_set_t *cpuset;
 128         unsigned int i;
 129         int nrcpus = perf_cpu_map__nr(cpu);
 130         size_t size;
 131
 132         threads_starting = params.nthreads;
 133
 134         cpuset = CPU_ALLOC(nrcpus);
 135         BUG_ON(!cpuset);
 136         size = CPU_ALLOC_SIZE(nrcpus);
 137
 138         /* create and block all threads */
 139         for (i = 0; i < params.nthreads; i++) {
 140                 CPU_ZERO_S(size, cpuset);
 141                 CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, size, cpuset);
 142
 143                 if (pthread_attr_setaffinity_np(&thread_attr, size, cpuset)) {
 144                         CPU_FREE(cpuset);
 145                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 146                 }
 147
 148                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) {
 149                         CPU_FREE(cpuset);
 150                         err(EXIT_FAILURE, "pthread_create");
 151                 }
 152         }
 153         CPU_FREE(cpuset);
 154 }
 155
 156 static void toggle_done(int sig __maybe_unused,
 157                         siginfo_t *info __maybe_unused,
 158                         void *uc __maybe_unused)
 159 {
 160         done = true;
 161 }
 162
 163 int bench_futex_requeue(int argc, const char **argv)
 164 {
 165         int ret = 0;
 166         unsigned int i, j;
 167         struct sigaction act;
 168         pthread_attr_t thread_attr;
 169         struct perf_cpu_map *cpu;
 170
 171         argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
 172         if (argc)
 173                 goto err;
 174
 175         cpu = perf_cpu_map__new(NULL);
 176         if (!cpu)
 177                 err(EXIT_FAILURE, "cpu_map__new");
 178
 179         memset(&act, 0, sizeof(act));
 180         sigfillset(&act.sa_mask);
 181         act.sa_sigaction = toggle_done;
 182         sigaction(SIGINT, &act, NULL);
 183
 184         if (params.mlockall) {
 185                 if (mlockall(MCL_CURRENT | MCL_FUTURE))
 186                         err(EXIT_FAILURE, "mlockall");
 187         }
 188
 189         if (!params.nthreads)
 190                 params.nthreads = perf_cpu_map__nr(cpu);
 191
 192         worker = calloc(params.nthreads, sizeof(*worker));
 193         if (!worker)
 194                 err(EXIT_FAILURE, "calloc");
 195
 196         if (!params.fshared)
 197                 futex_flag = FUTEX_PRIVATE_FLAG;
 198
 199         if (params.nrequeue > params.nthreads)
 200                 params.nrequeue = params.nthreads;
 201
 202         if (params.broadcast)
 203                 params.nrequeue = params.nthreads;
 204
 205         printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %s%p), "
 206                "%d at a time.\n\n",  getpid(), params.nthreads,
 207                params.fshared ? "shared":"private", &futex1,
 208                params.pi ? "PI ": "", &futex2, params.nrequeue);
 209
 210         init_stats(&requeued_stats);
 211         init_stats(&requeuetime_stats);
 212         pthread_attr_init(&thread_attr);
 213         mutex_init(&thread_lock);
 214         cond_init(&thread_parent);
 215         cond_init(&thread_worker);
 216
 217         for (j = 0; j < bench_repeat && !done; j++) {
 218                 unsigned int nrequeued = 0, wakeups = 0;
 219                 struct timeval start, end, runtime;
 220
 221                 /* create, launch & block all threads */
 222                 block_threads(worker, thread_attr, cpu);
 223
 224                 /* make sure all threads are already blocked */
 225                 mutex_lock(&thread_lock);
 226                 while (threads_starting)
 227                         cond_wait(&thread_parent, &thread_lock);
 228                 cond_broadcast(&thread_worker);
 229                 mutex_unlock(&thread_lock);
 230
 231                 usleep(100000);
 232
 233                 /* Ok, all threads are patiently blocked, start requeueing */
 234                 gettimeofday(&start, NULL);
 235                 while (nrequeued < params.nthreads) {
 236                         int r;
 237
 238                         /*
 239                          * For the regular non-pi case, do not wakeup any tasks
 240                          * blocked on futex1, allowing us to really measure
 241                          * futex_wait functionality. For the PI case the first
 242                          * waiter is always awoken.
 243                          */
 244                         if (!params.pi) {
 245                                 r = futex_cmp_requeue(&futex1, 0, &futex2, 0,
 246                                                       params.nrequeue,
 247                                                       futex_flag);
 248                         } else {
 249                                 r = futex_cmp_requeue_pi(&futex1, 0, &futex2,
 250                                                          params.nrequeue,
 251                                                          futex_flag);
 252                                 wakeups++; /* assume no error */
 253                         }
 254
 255                         if (r < 0)
 256                                 err(EXIT_FAILURE, "couldn't requeue from %p to %p",
 257                                     &futex1, &futex2);
 258
 259                         nrequeued += r;
 260                 }
 261
 262                 gettimeofday(&end, NULL);
 263                 timersub(&end, &start, &runtime);
 264
 265                 update_stats(&requeued_stats, nrequeued);
 266                 update_stats(&requeuetime_stats, runtime.tv_usec);
 267
 268                 if (!params.silent) {
 269                         if (!params.pi)
 270                                 printf("[Run %d]: Requeued %d of %d threads in "
 271                                        "%.4f ms\n", j + 1, nrequeued,
 272                                        params.nthreads,
 273                                        runtime.tv_usec / (double)USEC_PER_MSEC);
 274                         else {
 275                                 nrequeued -= wakeups;
 276                                 printf("[Run %d]: Awoke and Requeued (%d+%d) of "
 277                                        "%d threads in %.4f ms\n",
 278                                        j + 1, wakeups, nrequeued,
 279                                        params.nthreads,
 280                                        runtime.tv_usec / (double)USEC_PER_MSEC);
 281                         }
 282
 283                 }
 284
 285                 if (!params.pi) {
 286                         /* everybody should be blocked on futex2, wake'em up */
 287                         nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
 288                         if (params.nthreads != nrequeued)
 289                                 warnx("couldn't wakeup all tasks (%d/%d)",
 290                                       nrequeued, params.nthreads);
 291                 }
 292
 293                 for (i = 0; i < params.nthreads; i++) {
 294                         ret = pthread_join(worker[i], NULL);
 295                         if (ret)
 296                                 err(EXIT_FAILURE, "pthread_join");
 297                 }
 298         }
 299
 300         /* cleanup & report results */
 301         cond_destroy(&thread_parent);
 302         cond_destroy(&thread_worker);
 303         mutex_destroy(&thread_lock);
 304         pthread_attr_destroy(&thread_attr);
 305
 306         print_summary();
 307
 308         free(worker);
 309         perf_cpu_map__put(cpu);
 310         return ret;
 311 err:
 312         usage_with_options(bench_futex_requeue_usage, options);
 313         exit(EXIT_FAILURE);
 314 }