Quelle  futex-requeue.c   Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
 *
 * futex-requeue: Block a bunch of threads on futex1 and requeue them
 *                on futex2, N at a time.
 *
 * This program is particularly useful to measure the latency of nthread
 * requeues without waking up any tasks (in the non-pi case) -- thus
 * mimicking a regular futex_wait.
 */

/* For the CLR_() macros */
#include <string.h>
#include <pthread.h>

#include <signal.h>
#include "../util/mutex.h"
#include "../util/stat.h"
#include <subcmd/parse-options.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/time64.h>
#include <errno.h>
#include <perf/cpumap.h>
#include "bench.h"
#include "futex.h"

#include <err.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/mman.h>

static u_int32_t futex1 = 0, futex2 = 0;

static pthread_t *worker;
static bool done = false;
static struct mutex thread_lock;
static struct cond thread_parent, thread_worker;
static struct stats requeuetime_stats, requeued_stats;
static unsigned int threads_starting;
static int futex_flag = 0;

static struct bench_futex_parameters params = {
 .nbuckets = -1,
 /*
 * How many tasks to requeue at a time.
 * Default to 1 in order to make the kernel work more.
 */
 .nrequeue = 1,
};

static const struct option options[] = {
 OPT_INTEGER( 'b', "buckets", ¶ms.nbuckets, "Specify amount of hash buckets"),
 OPT_UINTEGER('t', "threads",  ¶ms.nthreads, "Specify amount of threads"),
 OPT_UINTEGER('q', "nrequeue", ¶ms.nrequeue, "Specify amount of threads to requeue at once"),
 OPT_BOOLEAN( 's', "silent",   ¶ms.silent, "Silent mode: do not display data/details"),
 OPT_BOOLEAN( 'S', "shared",   ¶ms.fshared, "Use shared futexes instead of private ones"),
 OPT_BOOLEAN( 'm', "mlockall", ¶ms.mlockall, "Lock all current and future memory"),
 OPT_BOOLEAN( 'B', "broadcast", ¶ms.broadcast, "Requeue all threads at once"),
 OPT_BOOLEAN( 'p', "pi", ¶ms.pi, "Use PI-aware variants of FUTEX_CMP_REQUEUE"),

 OPT_END()
};

static const char * const bench_futex_requeue_usage[] = {
 "perf bench futex requeue ",
 NULL
};

static void print_summary(void)
{
 double requeuetime_avg = avg_stats(&requeuetime_stats);
 double requeuetime_stddev = stddev_stats(&requeuetime_stats);
 unsigned int requeued_avg = avg_stats(&requeued_stats);

 printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
        requeued_avg,
        params.nthreads,
        requeuetime_avg / USEC_PER_MSEC,
        rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
 futex_print_nbuckets(¶ms);
}

static void *workerfn(void *arg __maybe_unused)
{
 int ret;

 mutex_lock(&thread_lock);
 threads_starting--;
 if (!threads_starting)
  cond_signal(&thread_parent);
 cond_wait(&thread_worker, &thread_lock);
 mutex_unlock(&thread_lock);

 while (1) {
  if (!params.pi) {
   ret = futex_wait(&futex1, 0, NULL, futex_flag);
   if (!ret)
    break;

   if (ret && errno != EAGAIN) {
    if (!params.silent)
     warnx("futex_wait");
    break;
   }
  } else {
   ret = futex_wait_requeue_pi(&futex1, 0, &futex2,
          NULL, futex_flag);
   if (!ret) {
    /* got the lock at futex2 */
    futex_unlock_pi(&futex2, futex_flag);
    break;
   }

   if (ret && errno != EAGAIN) {
    if (!params.silent)
     warnx("futex_wait_requeue_pi");
    break;
   }
  }
 }

 return NULL;
}

static void block_threads(pthread_t *w, struct perf_cpu_map *cpu)
{
 cpu_set_t *cpuset;
 unsigned int i;
 int nrcpus = cpu__max_cpu().cpu;
 size_t size;

 threads_starting = params.nthreads;

 cpuset = CPU_ALLOC(nrcpus);
 BUG_ON(!cpuset);
 size = CPU_ALLOC_SIZE(nrcpus);

 /* create and block all threads */
 for (i = 0; i < params.nthreads; i++) {
  pthread_attr_t thread_attr;

  pthread_attr_init(&thread_attr);
  CPU_ZERO_S(size, cpuset);
  CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, size, cpuset);

  if (pthread_attr_setaffinity_np(&thread_attr, size, cpuset)) {
   CPU_FREE(cpuset);
   err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
  }

  if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) {
   CPU_FREE(cpuset);
   err(EXIT_FAILURE, "pthread_create");
  }
  pthread_attr_destroy(&thread_attr);
 }
 CPU_FREE(cpuset);
}

static void toggle_done(int sig __maybe_unused,
   siginfo_t *info __maybe_unused,
   void *uc __maybe_unused)
{
 done = true;
}

int bench_futex_requeue(int argc, const char **argv)
{
 int ret = 0;
 unsigned int i, j;
 struct sigaction act;
 struct perf_cpu_map *cpu;

 argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
 if (argc)
  goto err;

 cpu = perf_cpu_map__new_online_cpus();
 if (!cpu)
  err(EXIT_FAILURE, "cpu_map__new");

 memset(&act, 0, sizeof(act));
 sigfillset(&act.sa_mask);
 act.sa_sigaction = toggle_done;
 sigaction(SIGINT, &act, NULL);

 if (params.mlockall) {
  if (mlockall(MCL_CURRENT | MCL_FUTURE))
   err(EXIT_FAILURE, "mlockall");
 }

 if (!params.nthreads)
  params.nthreads = perf_cpu_map__nr(cpu);

 worker = calloc(params.nthreads, sizeof(*worker));
 if (!worker)
  err(EXIT_FAILURE, "calloc");

 if (!params.fshared)
  futex_flag = FUTEX_PRIVATE_FLAG;

 if (params.nrequeue > params.nthreads)
  params.nrequeue = params.nthreads;

 if (params.broadcast)
  params.nrequeue = params.nthreads;

 futex_set_nbuckets_param(¶ms);

 printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %s%p), "
        "%d at a time.\n\n",  getpid(), params.nthreads,
        params.fshared ? "shared":"private", &futex1,
        params.pi ? "PI ": "", &futex2, params.nrequeue);

 init_stats(&requeued_stats);
 init_stats(&requeuetime_stats);
 mutex_init(&thread_lock);
 cond_init(&thread_parent);
 cond_init(&thread_worker);

 for (j = 0; j < bench_repeat && !done; j++) {
  unsigned int nrequeued = 0, wakeups = 0;
  struct timeval start, end, runtime;

  /* create, launch & block all threads */
  block_threads(worker, cpu);

  /* make sure all threads are already blocked */
  mutex_lock(&thread_lock);
  while (threads_starting)
   cond_wait(&thread_parent, &thread_lock);
  cond_broadcast(&thread_worker);
  mutex_unlock(&thread_lock);

  usleep(100000);

  /* Ok, all threads are patiently blocked, start requeueing */
  gettimeofday(&start, NULL);
  while (nrequeued < params.nthreads) {
   int r;

   /*
 * For the regular non-pi case, do not wakeup any tasks
 * blocked on futex1, allowing us to really measure
 * futex_wait functionality. For the PI case the first
 * waiter is always awoken.
 */
   if (!params.pi) {
    r = futex_cmp_requeue(&futex1, 0, &futex2, 0,
            params.nrequeue,
            futex_flag);
   } else {
    r = futex_cmp_requeue_pi(&futex1, 0, &futex2,
        params.nrequeue,
        futex_flag);
    wakeups++; /* assume no error */
   }

   if (r < 0)
    err(EXIT_FAILURE, "couldn't requeue from %p to %p",
        &futex1, &futex2);

   nrequeued += r;
  }

  gettimeofday(&end, NULL);
  timersub(&end, &start, &runtime);

  update_stats(&requeued_stats, nrequeued);
  update_stats(&requeuetime_stats, runtime.tv_usec);

  if (!params.silent) {
   if (!params.pi)
    printf("[Run %d]: Requeued %d of %d threads in "
           "%.4f ms\n", j + 1, nrequeued,
           params.nthreads,
           runtime.tv_usec / (double)USEC_PER_MSEC);
   else {
    nrequeued -= wakeups;
    printf("[Run %d]: Awoke and Requeued (%d+%d) of "
           "%d threads in %.4f ms\n",
           j + 1, wakeups, nrequeued,
           params.nthreads,
           runtime.tv_usec / (double)USEC_PER_MSEC);
   }

  }

  if (!params.pi) {
   /* everybody should be blocked on futex2, wake'em up */
   nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
   if (params.nthreads != nrequeued)
    warnx("couldn't wakeup all tasks (%d/%d)",
          nrequeued, params.nthreads);
  }

  for (i = 0; i < params.nthreads; i++) {
   ret = pthread_join(worker[i], NULL);
   if (ret)
    err(EXIT_FAILURE, "pthread_join");
  }
 }

 /* cleanup & report results */
 cond_destroy(&thread_parent);
 cond_destroy(&thread_worker);
 mutex_destroy(&thread_lock);

 print_summary();

 free(worker);
 perf_cpu_map__put(cpu);
 return ret;
err:
 usage_with_options(bench_futex_requeue_usage, options);
 exit(EXIT_FAILURE);
}