epoll-wait.c

// SPDX-License-Identifier: GPL-2.0
#ifdef HAVE_EVENTFD
/*
 * Copyright (C) 2018 Davidlohr Bueso.
 *
 * This program benchmarks concurrent epoll_wait(2) monitoring multiple
 * file descriptors under one or two load balancing models. The first,
 * and default, is the single/combined queueing (which refers to a single
 * epoll instance for N worker threads):
 *
 *                          |---> [worker A]
 *                          |---> [worker B]
 *        [combined queue]  .---> [worker C]
 *                          |---> [worker D]
 *                          |---> [worker E]
 *
 * While the second model, enabled via --multiq option, uses multiple
 * queueing (which refers to one epoll instance per worker). For example,
 * short lived tcp connections in a high throughput httpd server will
 * ditribute the accept()'ing  connections across CPUs. In this case each
 * worker does a limited  amount of processing.
 *
 *             [queue A]  ---> [worker]
 *             [queue B]  ---> [worker]
 *             [queue C]  ---> [worker]
 *             [queue D]  ---> [worker]
 *             [queue E]  ---> [worker]
 *
 * Naturally, the single queue will enforce more concurrency on the epoll
 * instance, and can therefore scale poorly compared to multiple queues.
 * However, this is a benchmark raw data and must be taken with a grain of
 * salt when choosing how to make use of sys_epoll.

 * Each thread has a number of private, nonblocking file descriptors,
 * referred to as fdmap. A writer thread will constantly be writing to
 * the fdmaps of all threads, minimizing each threads's chances of
 * epoll_wait not finding any ready read events and blocking as this
 * is not what we want to stress. The size of the fdmap can be adjusted
 * by the user; enlarging the value will increase the chances of
 * epoll_wait(2) blocking as the lineal writer thread will take "longer",
 * at least at a high level.
 *
 * Note that because fds are private to each thread, this workload does
 * not stress scenarios where multiple tasks are awoken per ready IO; ie:
 * EPOLLEXCLUSIVE semantics.
 *
 * The end result/metric is throughput: number of ops/second where an
 * operation consists of:
 *
 *   epoll_wait(2) + [others]
 *
 *        ... where [others] is the cost of re-adding the fd (EPOLLET),
 *            or rearming it (EPOLLONESHOT).
 *
 *
 * The purpose of this is program is that it be useful for measuring
 * kernel related changes to the sys_epoll, and not comparing different
 * IO polling methods, for example. Hence everything is very adhoc and
 * outputs raw microbenchmark numbers. Also this uses eventfd, similar
 * tools tend to use pipes or sockets, but the result is the same.
 */

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

#include <errno.h>
#include <inttypes.h>
#include <signal.h>
#include <stdlib.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/epoll.h>
#include <sys/eventfd.h>
#include <sys/types.h>
#include <internal/cpumap.h>
#include <perf/cpumap.h>

#include "../util/stat.h"
#include <subcmd/parse-options.h>
#include "bench.h"

#include <err.h>

#define printinfo(fmt, arg...) \
	do { if (__verbose) { printf(fmt, ## arg); fflush(stdout); } } while (0)

static unsigned int nthreads = 0;
static unsigned int nsecs    = 8;
struct timeval start, end, runtime;
static bool wdone, done, __verbose, randomize, nonblocking;

/*
 * epoll related shared variables.
 */

/* Maximum number of nesting allowed inside epoll sets */
#define EPOLL_MAXNESTS 4

static int epollfd;
static int *epollfdp;
static bool noaffinity;
static unsigned int nested = 0;
static bool et; /* edge-trigger */
static bool oneshot;
static bool multiq; /* use an epoll instance per thread */

/* amount of fds to monitor, per thread */
static unsigned int nfds = 64;

static pthread_mutex_t thread_lock;
static unsigned int threads_starting;
static struct stats throughput_stats;
static pthread_cond_t thread_parent, thread_worker;

struct worker {
	int tid;
	int epollfd; /* for --multiq */
	pthread_t thread;
	unsigned long ops;
	int *fdmap;
};

static const struct option options[] = {
	/* general benchmark options */
	OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
	OPT_UINTEGER('r', "runtime", &nsecs, "Specify runtime (in seconds)"),
	OPT_UINTEGER('f', "nfds",    &nfds,  "Specify amount of file descriptors to monitor for each thread"),
	OPT_BOOLEAN( 'n', "noaffinity",  &noaffinity,   "Disables CPU affinity"),
	OPT_BOOLEAN('R', "randomize", &randomize,   "Enable random write behaviour (default is lineal)"),
	OPT_BOOLEAN( 'v', "verbose", &__verbose, "Verbose mode"),

	/* epoll specific options */
	OPT_BOOLEAN( 'm', "multiq",  &multiq,   "Use multiple epoll instances (one per thread)"),
	OPT_BOOLEAN( 'B', "nonblocking", &nonblocking, "Nonblocking epoll_wait(2) behaviour"),
	OPT_UINTEGER( 'N', "nested",  &nested,   "Nesting level epoll hierarchy (default is 0, no nesting)"),
	OPT_BOOLEAN( 'S', "oneshot",  &oneshot,   "Use EPOLLONESHOT semantics"),
	OPT_BOOLEAN( 'E', "edge",  &et,   "Use Edge-triggered interface (default is LT)"),

	OPT_END()
};

static const char * const bench_epoll_wait_usage[] = {
	"perf bench epoll wait <options>",
	NULL
};


/*
 * Arrange the N elements of ARRAY in random order.
 * Only effective if N is much smaller than RAND_MAX;
 * if this may not be the case, use a better random
 * number generator. -- Ben Pfaff.
 */
static void shuffle(void *array, size_t n, size_t size)
{
	char *carray = array;
	void *aux;
	size_t i;

	if (n <= 1)
		return;

	aux = calloc(1, size);
	if (!aux)
		err(EXIT_FAILURE, "calloc");

	for (i = 1; i < n; ++i) {
		size_t j =   i + rand() / (RAND_MAX / (n - i) + 1);
		j *= size;

		memcpy(aux, &carray[j], size);
		memcpy(&carray[j], &carray[i*size], size);
		memcpy(&carray[i*size], aux, size);
	}

	free(aux);
}


static void *workerfn(void *arg)
{
	int fd, ret, r;
	struct worker *w = (struct worker *) arg;
	unsigned long ops = w->ops;
	struct epoll_event ev;
	uint64_t val;
	int to = nonblocking? 0 : -1;
	int efd = multiq ? w->epollfd : epollfd;

	pthread_mutex_lock(&thread_lock);
	threads_starting--;
	if (!threads_starting)
		pthread_cond_signal(&thread_parent);
	pthread_cond_wait(&thread_worker, &thread_lock);
	pthread_mutex_unlock(&thread_lock);

	do {
		/*
		 * Block undefinitely waiting for the IN event.
		 * In order to stress the epoll_wait(2) syscall,
		 * call it event per event, instead of a larger
		 * batch (max)limit.
		 */
		do {
			ret = epoll_wait(efd, &ev, 1, to);
		} while (ret < 0 && errno == EINTR);
		if (ret < 0)
			err(EXIT_FAILURE, "epoll_wait");

		fd = ev.data.fd;

		do {
			r = read(fd, &val, sizeof(val));
		} while (!done && (r < 0 && errno == EAGAIN));

		if (et) {
			ev.events = EPOLLIN | EPOLLET;
			ret = epoll_ctl(efd, EPOLL_CTL_ADD, fd, &ev);
		}

		if (oneshot) {
			/* rearm the file descriptor with a new event mask */
			ev.events |= EPOLLIN | EPOLLONESHOT;
			ret = epoll_ctl(efd, EPOLL_CTL_MOD, fd, &ev);
		}

		ops++;
	}  while (!done);

	if (multiq)
		close(w->epollfd);

	w->ops = ops;
	return NULL;
}

static void nest_epollfd(struct worker *w)
{
	unsigned int i;
	struct epoll_event ev;
	int efd = multiq ? w->epollfd : epollfd;

	if (nested > EPOLL_MAXNESTS)
		nested = EPOLL_MAXNESTS;

	epollfdp = calloc(nested, sizeof(*epollfdp));
	if (!epollfdp)
		err(EXIT_FAILURE, "calloc");

	for (i = 0; i < nested; i++) {
		epollfdp[i] = epoll_create(1);
		if (epollfdp[i] < 0)
			err(EXIT_FAILURE, "epoll_create");
	}

	ev.events = EPOLLHUP; /* anything */
	ev.data.u64 = i; /* any number */

	for (i = nested - 1; i; i--) {
		if (epoll_ctl(epollfdp[i - 1], EPOLL_CTL_ADD,
			      epollfdp[i], &ev) < 0)
			err(EXIT_FAILURE, "epoll_ctl");
	}

	if (epoll_ctl(efd, EPOLL_CTL_ADD, *epollfdp, &ev) < 0)
		err(EXIT_FAILURE, "epoll_ctl");
}

static void toggle_done(int sig __maybe_unused,
			siginfo_t *info __maybe_unused,
			void *uc __maybe_unused)
{
	/* inform all threads that we're done for the day */
	done = true;
	gettimeofday(&end, NULL);
	timersub(&end, &start, &runtime);
}

static void print_summary(void)
{
	unsigned long avg = avg_stats(&throughput_stats);
	double stddev = stddev_stats(&throughput_stats);

	printf("\nAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
	       avg, rel_stddev_stats(stddev, avg),
	       (int) runtime.tv_sec);
}

static int do_threads(struct worker *worker, struct perf_cpu_map *cpu)
{
	pthread_attr_t thread_attr, *attrp = NULL;
	cpu_set_t cpuset;
	unsigned int i, j;
	int ret = 0, events = EPOLLIN;

	if (oneshot)
		events |= EPOLLONESHOT;
	if (et)
		events |= EPOLLET;

	printinfo("starting worker/consumer %sthreads%s\n",
		  noaffinity ?  "":"CPU affinity ",
		  nonblocking ? " (nonblocking)":"");
	if (!noaffinity)
		pthread_attr_init(&thread_attr);

	for (i = 0; i < nthreads; i++) {
		struct worker *w = &worker[i];

		if (multiq) {
			w->epollfd = epoll_create(1);
			if (w->epollfd < 0)
				err(EXIT_FAILURE, "epoll_create");

			if (nested)
				nest_epollfd(w);
		}

		w->tid = i;
		w->fdmap = calloc(nfds, sizeof(int));
		if (!w->fdmap)
			return 1;

		for (j = 0; j < nfds; j++) {
			int efd = multiq ? w->epollfd : epollfd;
			struct epoll_event ev;

			w->fdmap[j] = eventfd(0, EFD_NONBLOCK);
			if (w->fdmap[j] < 0)
				err(EXIT_FAILURE, "eventfd");

			ev.data.fd = w->fdmap[j];
			ev.events = events;

			ret = epoll_ctl(efd, EPOLL_CTL_ADD,
					w->fdmap[j], &ev);
			if (ret < 0)
				err(EXIT_FAILURE, "epoll_ctl");
		}

		if (!noaffinity) {
			CPU_ZERO(&cpuset);
			CPU_SET(cpu->map[i % cpu->nr], &cpuset);

			ret = pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset);
			if (ret)
				err(EXIT_FAILURE, "pthread_attr_setaffinity_np");

			attrp = &thread_attr;
		}

		ret = pthread_create(&w->thread, attrp, workerfn,
				     (void *)(struct worker *) w);
		if (ret)
			err(EXIT_FAILURE, "pthread_create");
	}

	if (!noaffinity)
		pthread_attr_destroy(&thread_attr);

	return ret;
}

static void *writerfn(void *p)
{
	struct worker *worker = p;
	size_t i, j, iter;
	const uint64_t val = 1;
	ssize_t sz;
	struct timespec ts = { .tv_sec = 0,
			       .tv_nsec = 500 };

	printinfo("starting writer-thread: doing %s writes ...\n",
		  randomize? "random":"lineal");

	for (iter = 0; !wdone; iter++) {
		if (randomize) {
			shuffle((void *)worker, nthreads, sizeof(*worker));
		}

		for (i = 0; i < nthreads; i++) {
			struct worker *w = &worker[i];

			if (randomize) {
				shuffle((void *)w->fdmap, nfds, sizeof(int));
			}

			for (j = 0; j < nfds; j++) {
				do {
					sz = write(w->fdmap[j], &val, sizeof(val));
				} while (!wdone && (sz < 0 && errno == EAGAIN));
			}
		}

		nanosleep(&ts, NULL);
	}

	printinfo("exiting writer-thread (total full-loops: %zd)\n", iter);
	return NULL;
}

static int cmpworker(const void *p1, const void *p2)
{

	struct worker *w1 = (struct worker *) p1;
	struct worker *w2 = (struct worker *) p2;
	return w1->tid > w2->tid;
}

int bench_epoll_wait(int argc, const char **argv)
{
	int ret = 0;
	struct sigaction act;
	unsigned int i;
	struct worker *worker = NULL;
	struct perf_cpu_map *cpu;
	pthread_t wthread;
	struct rlimit rl, prevrl;

	argc = parse_options(argc, argv, options, bench_epoll_wait_usage, 0);
	if (argc) {
		usage_with_options(bench_epoll_wait_usage, options);
		exit(EXIT_FAILURE);
	}

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

	cpu = perf_cpu_map__new(NULL);
	if (!cpu)
		goto errmem;

	/* a single, main epoll instance */
	if (!multiq) {
		epollfd = epoll_create(1);
		if (epollfd < 0)
			err(EXIT_FAILURE, "epoll_create");

		/*
		 * Deal with nested epolls, if any.
		 */
		if (nested)
			nest_epollfd(NULL);
	}

	printinfo("Using %s queue model\n", multiq ? "multi" : "single");
	printinfo("Nesting level(s): %d\n", nested);

	/* default to the number of CPUs and leave one for the writer pthread */
	if (!nthreads)
		nthreads = cpu->nr - 1;

	worker = calloc(nthreads, sizeof(*worker));
	if (!worker) {
		goto errmem;
	}

	if (getrlimit(RLIMIT_NOFILE, &prevrl))
		err(EXIT_FAILURE, "getrlimit");
	rl.rlim_cur = rl.rlim_max = nfds * nthreads * 2 + 50;
	printinfo("Setting RLIMIT_NOFILE rlimit from %" PRIu64 " to: %" PRIu64 "\n",
		  (uint64_t)prevrl.rlim_max, (uint64_t)rl.rlim_max);
	if (setrlimit(RLIMIT_NOFILE, &rl) < 0)
		err(EXIT_FAILURE, "setrlimit");

	printf("Run summary [PID %d]: %d threads monitoring%s on "
	       "%d file-descriptors for %d secs.\n\n",
	       getpid(), nthreads, oneshot ? " (EPOLLONESHOT semantics)": "", nfds, nsecs);

	init_stats(&throughput_stats);
	pthread_mutex_init(&thread_lock, NULL);
	pthread_cond_init(&thread_parent, NULL);
	pthread_cond_init(&thread_worker, NULL);

	threads_starting = nthreads;

	gettimeofday(&start, NULL);

	do_threads(worker, cpu);

	pthread_mutex_lock(&thread_lock);
	while (threads_starting)
		pthread_cond_wait(&thread_parent, &thread_lock);
	pthread_cond_broadcast(&thread_worker);
	pthread_mutex_unlock(&thread_lock);

	/*
	 * At this point the workers should be blocked waiting for read events
	 * to become ready. Launch the writer which will constantly be writing
	 * to each thread's fdmap.
	 */
	ret = pthread_create(&wthread, NULL, writerfn,
			     (void *)(struct worker *) worker);
	if (ret)
		err(EXIT_FAILURE, "pthread_create");

	sleep(nsecs);
	toggle_done(0, NULL, NULL);
	printinfo("main thread: toggling done\n");

	sleep(1); /* meh */
	wdone = true;
	ret = pthread_join(wthread, NULL);
	if (ret)
		err(EXIT_FAILURE, "pthread_join");

	/* cleanup & report results */
	pthread_cond_destroy(&thread_parent);
	pthread_cond_destroy(&thread_worker);
	pthread_mutex_destroy(&thread_lock);

	/* sort the array back before reporting */
	if (randomize)
		qsort(worker, nthreads, sizeof(struct worker), cmpworker);

	for (i = 0; i < nthreads; i++) {
		unsigned long t = worker[i].ops/runtime.tv_sec;

		update_stats(&throughput_stats, t);

		if (nfds == 1)
			printf("[thread %2d] fdmap: %p [ %04ld ops/sec ]\n",
			       worker[i].tid, &worker[i].fdmap[0], t);
		else
			printf("[thread %2d] fdmap: %p ... %p [ %04ld ops/sec ]\n",
			       worker[i].tid, &worker[i].fdmap[0],
			       &worker[i].fdmap[nfds-1], t);
	}

	print_summary();

	close(epollfd);
	return ret;
errmem:
	err(EXIT_FAILURE, "calloc");
}
#endif // HAVE_EVENTFD