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

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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: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221129215926.442895-4-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Brown 2022-11-29 21:59:25 +00:00 committed by Will Deacon
parent 92145d88ce
commit c4e8720f2e
1 changed files with 18 additions and 9 deletions
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27
tools/testing/selftests/arm64/fp/fp-stress.c
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@ -39,6 +39,8 @@ struct child_data {
static int epoll_fd; static int epoll_fd;
static struct child_data *children; static struct child_data *children;
static struct epoll_event *evs;
static int tests;
static int num_children; static int num_children;
static bool terminate; 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 */ /* Handle any pending output without blocking */
static void drain_output(bool flush) static void drain_output(bool flush)
{ {
struct epoll_event ev;
int ret = 1; int ret = 1;
int i;
while (ret > 0) { while (ret > 0) {
ret = epoll_wait(epoll_fd, &ev, 1, 0); ret = epoll_wait(epoll_fd, evs, tests, 0);
if (ret < 0) { if (ret < 0) {
if (errno == EINTR) if (errno == EINTR)
continue; continue;
@ -405,8 +407,8 @@ static void drain_output(bool flush)
strerror(errno), errno); strerror(errno), errno);
} }
if (ret == 1) for (i = 0; i < ret; i++)
child_output(ev.data.ptr, ev.events, flush); child_output(evs[i].data.ptr, evs[i].events, flush);
} }
} }
@ -419,12 +421,11 @@ int main(int argc, char **argv)
{ {
int ret; int ret;
int timeout = 10; int timeout = 10;
int cpus, tests, i, j, c; int cpus, i, j, c;
int sve_vl_count, sme_vl_count, fpsimd_per_cpu; int sve_vl_count, sme_vl_count, fpsimd_per_cpu;
bool all_children_started = false; bool all_children_started = false;
int seen_children; int seen_children;
int sve_vls[MAX_VLS], sme_vls[MAX_VLS]; int sve_vls[MAX_VLS], sme_vls[MAX_VLS];
struct epoll_event ev;
struct sigaction sa; struct sigaction sa;
while ((c = getopt_long(argc, argv, "t:", options, NULL)) != -1) { 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", ksft_print_msg("Failed to install SIGCHLD handler: %s (%d)\n",
strerror(errno), errno); 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 (i = 0; i < cpus; i++) {
for (j = 0; j < fpsimd_per_cpu; j++) for (j = 0; j < fpsimd_per_cpu; j++)
start_fpsimd(&children[num_children++], i, 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 * useful in emulation where we will both be slow and
* likely to have a large set of VLs. * 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 (ret < 0) {
if (errno == EINTR) if (errno == EINTR)
continue; continue;
@ -552,8 +558,11 @@ int main(int argc, char **argv)
} }
/* Output? */ /* Output? */
if (ret == 1) { if (ret > 0) {
child_output(ev.data.ptr, ev.events, false); for (i = 0; i < ret; i++) {
child_output(evs[i].data.ptr, evs[i].events,
false);
}
continue; continue;
} }