Commit c4e8720f authored by Mark Brown's avatar Mark Brown Committed by Will Deacon
Browse files

kselftest/arm64: Allow epoll_wait() to return more than one result 



When everything is starting up we are likely to have a lot of child
processes producing output at once.  This means that we can reduce
overhead a bit by allowing epoll_wait() to return more than one
descriptor at once, it cuts down on the number of system calls we need
to do which on virtual platforms where the syscall overhead is a bit
more noticable and we're likely to have a lot more children active can
make a small but noticable difference.

On physical platforms the relatively small number of processes being run
and vastly improved speeds push the effects of this change into the
noise.

Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221129215926.442895-4-broonie@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 92145d88

tools/testing/selftests/arm64/fp/fp-stress.c

+18 −9
Original line number Diff line number Diff line
@@ -39,6 +39,8 @@ struct child_data { 


static int epoll_fd;

static struct child_data *children;

static struct epoll_event *evs;

static int tests;

static int num_children;

static bool terminate;
@@ -393,11 +395,11 @@ static void probe_vls(int vls[], int *vl_count, int set_vl) 
/* Handle any pending output without blocking */

static void drain_output(bool flush)

{

	struct epoll_event ev;

	int ret = 1;

	int i;



	while (ret > 0) {

		ret = epoll_wait(epoll_fd, &ev, 1, 0);

		ret = epoll_wait(epoll_fd, evs, tests, 0);

		if (ret < 0) {

			if (errno == EINTR)

				continue;
@@ -405,8 +407,8 @@ static void drain_output(bool flush) 
				       strerror(errno), errno);

		}



		if (ret == 1)

			child_output(ev.data.ptr, ev.events, flush);

		for (i = 0; i < ret; i++)

			child_output(evs[i].data.ptr, evs[i].events, flush);

	}

}
@@ -419,12 +421,11 @@ int main(int argc, char **argv) 
{

	int ret;

	int timeout = 10;

	int cpus, tests, i, j, c;

	int cpus, i, j, c;

	int sve_vl_count, sme_vl_count, fpsimd_per_cpu;

	bool all_children_started = false;

	int seen_children;

	int sve_vls[MAX_VLS], sme_vls[MAX_VLS];

	struct epoll_event ev;

	struct sigaction sa;



	while ((c = getopt_long(argc, argv, "t:", options, NULL)) != -1) {
@@ -510,6 +511,11 @@ int main(int argc, char **argv) 
		ksft_print_msg("Failed to install SIGCHLD handler: %s (%d)\n",

			       strerror(errno), errno);



	evs = calloc(tests, sizeof(*evs));

	if (!evs)

		ksft_exit_fail_msg("Failed to allocated %d epoll events\n",

				   tests);



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

		for (j = 0; j < fpsimd_per_cpu; j++)

			start_fpsimd(&children[num_children++], i, j);
@@ -543,7 +549,7 @@ int main(int argc, char **argv) 
		 * useful in emulation where we will both be slow and

		 * likely to have a large set of VLs.

		 */

		ret = epoll_wait(epoll_fd, &ev, 1, 1000);

		ret = epoll_wait(epoll_fd, evs, tests, 1000);

		if (ret < 0) {

			if (errno == EINTR)

				continue;
@@ -552,8 +558,11 @@ int main(int argc, char **argv) 
		}



		/* Output? */

		if (ret == 1) {

			child_output(ev.data.ptr, ev.events, false);

		if (ret > 0) {

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

				child_output(evs[i].data.ptr, evs[i].events,

					     false);

			}

			continue;

		}