When the next interval is too far in the future, then now < next, and the
elapsed time calcdiff(now, next) is negative. If such a situation occurs, it is
obvious the calculation of the next interval was wrong, and we rewind it until
we find a positive value.
This bug can be reproduced by setting a very short interval, such as 1us:
Without the patch:
./cyclictest -i 1
T: 0 ( 8429) P: 0 I:1 C:1099294 Min: 0 Act: -34 Avg:-9223372036854775808 Max: -1
With the patch:
./cyclictest -i 1
T: 0 ( 8665) P: 0 I:1 C: 419151 Min: 0 Act: 0 Avg: 0 Max: 76
Signed-off-by: Francis Giraldeau <francis.giraldeau@xxxxxxxxx>
---
src/cyclictest/cyclictest.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
index 34053c5..151b0eb 100644
--- a/src/cyclictest/cyclictest.c
+++ b/src/cyclictest/cyclictest.c
@@ -914,6 +914,16 @@ void *timerthread(void *param)
goto out;
}
+ // the next interval was too far in the future, rewind it
+ while (calcdiff_ns(now, next) < 0) {
+ next.tv_sec -= interval.tv_sec;
+ next.tv_nsec -= interval.tv_nsec;
+ if (next.tv_nsec < 0) {
+ next.tv_sec--;
+ next.tv_nsec += NSEC_PER_SEC;
+ }
+ }
+
if (use_nsecs)
diff = calcdiff_ns(now, next);
else
--
2.7.4
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
