Commit 3e2d4df5 authored by Brian Geffon's avatar Brian Geffon Committed by Namhyung Kim
Browse files

perf tools: sched-pipe bench: add (-n) nonblocking benchmark 

The -n mode will benchmark pipes in a non-blocking mode using
epoll_wait.

This specific mode was added to demonstrate the broken sync nature
of epoll: https://lore.kernel.org/lkml/20240426-zupfen-jahrzehnt-5be786bcdf04@brauner



Signed-off-by: default avatarBrian Geffon <bgeffon@google.com>
Reviewed-by: default avatarIan Rogers <irogers@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20241016190009.866615-1-bgeffon@google.com


Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent 915a3776

tools/perf/bench/sched-pipe.c

+36 −7
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#include <errno.h>

#include <fcntl.h>

#include <assert.h>

#include <sys/epoll.h>

#include <sys/time.h>

#include <sys/types.h>

#include <sys/syscall.h>
@@ -34,6 +35,8 @@ struct thread_data { 
	int			nr;

	int			pipe_read;

	int			pipe_write;

	struct epoll_event      epoll_ev;

	int			epoll_fd;

	bool			cgroup_failed;

	pthread_t		pthread;

};
@@ -44,6 +47,7 @@ static int loops = LOOPS_DEFAULT; 
/* Use processes by default: */

static bool			threaded;



static bool			nonblocking;

static char			*cgrp_names[2];

static struct cgroup		*cgrps[2];
@@ -81,6 +85,7 @@ static int parse_two_cgroups(const struct option *opt __maybe_unused, 
}



static const struct option options[] = {

	OPT_BOOLEAN('n', "nonblocking",	&nonblocking,	"Use non-blocking operations"),

	OPT_INTEGER('l', "loop",	&loops,		"Specify number of loops"),

	OPT_BOOLEAN('T', "threaded",	&threaded,	"Specify threads/process based task setup"),

	OPT_CALLBACK('G', "cgroups", NULL, "SEND,RECV",
@@ -165,11 +170,25 @@ static void exit_cgroup(int nr) 
	free(cgrp_names[nr]);

}



static inline int read_pipe(struct thread_data *td)

{

	int ret, m;

retry:

	if (nonblocking) {

		ret = epoll_wait(td->epoll_fd, &td->epoll_ev, 1, -1);

		if (ret < 0)

			return ret;

	}

	ret = read(td->pipe_read, &m, sizeof(int));

	if (nonblocking && ret < 0 && errno == EWOULDBLOCK)

		goto retry;

	return ret;

}



static void *worker_thread(void *__tdata)

{

	struct thread_data *td = __tdata;

	int m = 0, i;

	int ret;

	int i, ret, m = 0;



	ret = enter_cgroup(td->nr);

	if (ret < 0) {
@@ -177,16 +196,23 @@ static void *worker_thread(void *__tdata) 
		return NULL;

	}



	if (nonblocking) {

		td->epoll_ev.events = EPOLLIN;

		td->epoll_fd = epoll_create(1);

		BUG_ON(td->epoll_fd < 0);

		BUG_ON(epoll_ctl(td->epoll_fd, EPOLL_CTL_ADD, td->pipe_read, &td->epoll_ev) < 0);

	}



	for (i = 0; i < loops; i++) {

		if (!td->nr) {

			ret = read(td->pipe_read, &m, sizeof(int));

			ret = read_pipe(td);

			BUG_ON(ret != sizeof(int));

			ret = write(td->pipe_write, &m, sizeof(int));

			BUG_ON(ret != sizeof(int));

		} else {

			ret = write(td->pipe_write, &m, sizeof(int));

			BUG_ON(ret != sizeof(int));

			ret = read(td->pipe_read, &m, sizeof(int));

			ret = read_pipe(td);

			BUG_ON(ret != sizeof(int));

		}

	}
@@ -209,13 +235,16 @@ int bench_sched_pipe(int argc, const char **argv) 
	 * discarding returned value of read(), write()

	 * causes error in building environment for perf

	 */

	int __maybe_unused ret, wait_stat;

	int __maybe_unused ret, wait_stat, flags = 0;

	pid_t pid, retpid __maybe_unused;



	argc = parse_options(argc, argv, options, bench_sched_pipe_usage, 0);



	BUG_ON(pipe(pipe_1));

	BUG_ON(pipe(pipe_2));

	if (nonblocking)

		flags |= O_NONBLOCK;



	BUG_ON(pipe2(pipe_1, flags));

	BUG_ON(pipe2(pipe_2, flags));



	gettimeofday(&start, NULL);