[PATCH 5/5] testsuite/smokey: posix_clock: prevent false positive in timing-depending test

Philippe Gerum rpm at xenomai.org
Mon Jan 14 18:35:22 CET 2019


clock_decrease_after_periodic_timer_first_tick checks that periodic
interval timers based on CLOCK_REALTIME are not (pathologically)
affected by the epoch going backwards.

To this end, we measure the actual time observed between two ticks of
a periodic timer based on CLOCK_REALTIME with a call to
clock_settime() injecting a negative offset in between, equivalent to
five ticks.

Due to processing delays induced by clock_settime() and other latency,
we could observe a duration which exceeds a tick by a few tenths of
microseconds. Since we can't anticipate the amount of latency
involved, let's accept a longer delay of at most two ticks.

This is still correct from the standpoint of the test, which verifies
that no correlation exists between the clock offset injected by
clock_settime() and the delay until the next tick generated by the
affected clock.

Signed-off-by: Philippe Gerum <rpm at xenomai.org>
---
 testsuite/smokey/posix-clock/posix-clock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/testsuite/smokey/posix-clock/posix-clock.c b/testsuite/smokey/posix-clock/posix-clock.c
index f672a9d52..3a638d41f 100644
--- a/testsuite/smokey/posix-clock/posix-clock.c
+++ b/testsuite/smokey/posix-clock/posix-clock.c
@@ -417,7 +417,7 @@ static int clock_decrease_after_periodic_timer_first_tick(void)
 
 	diff = now.tv_sec * 1000000000ULL + now.tv_nsec -
 		(timer.it_value.tv_sec * 1000000000ULL + timer.it_value.tv_nsec);
-	if (!smokey_assert(diff < 1000000000))
+	if (!smokey_assert(diff < 2000000000))
 		return -EINVAL;
 	
 	ret = smokey_check_errno(read(t, &ticks, sizeof(ticks)));
-- 
2.17.2




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