Re: [PATCH v6 2/2] selftests/timers/posix_timers: Test delivery of signals across threads

On 3/16/23 5:30 PM, Marco Elver wrote:

From: Dmitry Vyukov dvyukov@google.com

Test that POSIX timers using CLOCK_PROCESS_CPUTIME_ID eventually deliver a signal to all running threads. This effectively tests that the kernel doesn't prefer any one thread (or subset of threads) for signal delivery.

Signed-off-by: Dmitry Vyukov dvyukov@google.com Signed-off-by: Marco Elver elver@google.com

---

v6:

• Update wording on what the test aims to test.
• Fix formatting per checkpatch.pl.

---

tools/testing/selftests/timers/posix_timers.c | 77 +++++++++++++++++++ 1 file changed, 77 insertions(+)

diff --git a/tools/testing/selftests/timers/posix_timers.c b/tools/testing/selftests/timers/posix_timers.c index 0ba500056e63..8a17c0e8d82b 100644 --- a/tools/testing/selftests/timers/posix_timers.c +++ b/tools/testing/selftests/timers/posix_timers.c @@ -188,6 +188,80 @@ static int check_timer_create(int which) return 0; } +int remain; +__thread int got_signal;

+static void *distribution_thread(void *arg) +{

• while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
• return NULL;

+}

+static void distribution_handler(int nr) +{

• if (!__atomic_exchange_n(&got_signal, 1, __ATOMIC_RELAXED))

• __atomic_fetch_sub(&remain, 1, __ATOMIC_RELAXED);
  

+}

+/*

• • Test that all running threads _eventually_ receive CLOCK_PROCESS_CPUTIME_ID
• • timer signals. This primarily tests that the kernel does not favour any one.
• */

+static int check_timer_distribution(void) +{

• int err, i;
• timer_t id;
• const int nthreads = 10;
• pthread_t threads[nthreads];
• struct itimerspec val = {

• .it_value.tv_sec = 0,
  

• .it_value.tv_nsec = 1000 * 1000,
  

• .it_interval.tv_sec = 0,
  

• .it_interval.tv_nsec = 1000 * 1000,
  

• };
• printf("Check timer_create() per process signal distribution... ");

Use APIs from kselftest.h. Use ksft_print_msg() here.

• fflush(stdout);
• remain = nthreads + 1; /* worker threads + this thread */
• signal(SIGALRM, distribution_handler);
• err = timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
• if (err < 0) {

• perror("Can't create timer\n");
  

ksft_perror() here

• return -1;
  

• }
• err = timer_settime(id, 0, &val, NULL);
• if (err < 0) {

• perror("Can't set timer\n");
  

• return -1;
  

• }
• for (i = 0; i < nthreads; i++) {

• if (pthread_create(&threads[i], NULL, distribution_thread, NULL)) {
  

• 	perror("Can't create thread\n");
  

• 	return -1;
  

• }
  

• }
• /* Wait for all threads to receive the signal. */
• while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
• for (i = 0; i < nthreads; i++) {

• if (pthread_join(threads[i], NULL)) {
  

• 	perror("Can't join thread\n");
  

• 	return -1;
  

• }
  

• }
• if (timer_delete(id)) {

• perror("Can't delete timer\n");
  

• return -1;
  

• }
• printf("[OK]\n");

ksft_test_result or _pass variant as needed?

• return 0;

+}

int main(int argc, char **argv) { printf("Testing posix timers. False negative may happen on CPU execution \n"); @@ -217,5 +291,8 @@ int main(int argc, char **argv) if (check_timer_create(CLOCK_PROCESS_CPUTIME_ID) < 0) return ksft_exit_fail();

• if (check_timer_distribution() < 0)

• return ksft_exit_fail();
  

• return ksft_exit_pass();

}