[PATCH] hrtimers: Special-case zero length sleeps

Matthew Garrett
2011-09-29T14:59:29Z

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 <mjg@redhat.com>
---
kernel/hrtimer.c | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index a9205e3..0bb70a7 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))
--
1.7.6.4