[PATCH 3.19 165/177] sched: Fix hrtick_start() on UP

[Greg Kroah-Hartman]

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>

commit 868933359a3bdda25b562e9d41bce7071edc1b08 upstream.

The commit 177ef2a6315e ("sched/deadline: Fix a precision problem in
the microseconds range") forgot to change the UP version of
hrtick_start(), do so now.

Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
Fixes: 177ef2a6315e ("sched/deadline: Fix a precision problem in the microseconds range")
[ Fixed the changelog. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1416962647-76792-7-git-send-email-wanpeng.li@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/sched/core.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -490,6 +490,11 @@ static __init void init_hrtick(void)
  */
 void hrtick_start(struct rq *rq, u64 delay)
 {
+	/*
+	 * Don't schedule slices shorter than 10000ns, that just
+	 * doesn't make sense. Rely on vruntime for fairness.
+	 */
+	delay = max_t(u64, delay, 10000LL);
 	__hrtimer_start_range_ns(&rq->hrtick_timer, ns_to_ktime(delay), 0,
 			HRTIMER_MODE_REL_PINNED, 0);
 }


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