From: Matthew Garrett Date: Wed, 16 Nov 2011 23:41:07 +0000 (+1100) Subject: hrtimers: Special-case zero length sleeps X-Git-Tag: next-20111128~1^2~103 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=bb30cb6063ffc9972188fcba098663285adac53d;p=karo-tx-linux.git hrtimers: Special-case zero length sleeps sleep(0) is a common construct used by applications that want to trigger the scheduler. sched_yield() might make more sense, but only appeared in POSIX.1-2001 and so plenty of example code still uses the sleep(0) form. This wouldn't normally be a problem, but it means that event-driven applications that are merely trying to avoid starving other processes may actually end up sleeping due to having large timer_slack values. Special- casing this seems reasonable. Signed-off-by: Matthew Garrett Cc: Thomas Gleixner Cc: Arjan van de Ven Signed-off-by: Andrew Morton --- diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c index 422e567eecf6..5e30317b7c68 100644 --- a/kernel/hrtimer.c +++ b/kernel/hrtimer.c @@ -1566,6 +1566,14 @@ long hrtimer_nanosleep(struct timespec *rqtp, struct timespec __user *rmtp, if (rt_task(current)) slack = 0; + /* + * Applications will often sleep(0) to indicate that they wish to + * be scheduled. Special case that to avoid actually putting them + * to sleep for the duration of the slack. + */ + if (rqtp->tv_sec == 0 && rqtp->tv_nsec == 0) + slack = 0; + hrtimer_init_on_stack(&t.timer, clockid, mode); hrtimer_set_expires_range_ns(&t.timer, timespec_to_ktime(*rqtp), slack); if (do_nanosleep(&t, mode))