futex-requeue.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2013  Davidlohr Bueso <[email protected]>
 *
 * 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", &params.nbuckets, "Specify amount of hash buckets"),
	OPT_UINTEGER('t', "threads",  &params.nthreads, "Specify amount of threads"),
	OPT_UINTEGER('q', "nrequeue", &params.nrequeue, "Specify amount of threads to requeue at once"),
	OPT_BOOLEAN( 's', "silent",   &params.silent, "Silent mode: do not display data/details"),
	OPT_BOOLEAN( 'S', "shared",   &params.fshared, "Use shared futexes instead of private ones"),
	OPT_BOOLEAN( 'm', "mlockall", &params.mlockall, "Lock all current and future memory"),
	OPT_BOOLEAN( 'B', "broadcast", &params.broadcast, "Requeue all threads at once"),
	OPT_BOOLEAN( 'p', "pi", &params.pi, "Use PI-aware variants of FUTEX_CMP_REQUEUE"),

	OPT_END()
};

static const char * const bench_futex_requeue_usage[] = {
	"perf bench futex requeue <options>",
	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(&params);
}

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(&params);

	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);
}