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[PATCH 4.2.y-ckt 49/64] tick/nohz: Set the correct expiry when switching to nohz/lowres mode

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  [PATCH 4.2.y-ckt 49/64] tick/nohz: Set the correct expiry when switching to nohz/lowres mode Kamal Mostafa <kamal@canonical.com> - 2016-02-05 00:00 +0100

#1327298 — [PATCH 4.2.y-ckt 49/64] tick/nohz: Set the correct expiry when switching to nohz/lowres mode

4.2.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Wanpeng Li <kernellwp@gmail.com>

commit 1ca8ec532fc2d986f1f4a319857bb18e0c9739b4 upstream.

commit 0ff53d096422 sets the next tick interrupt to the last jiffies update,
i.e. in the past, because the forward operation is invoked before the set
operation. There is no resulting damage (yet), but we get an extra pointless
tick interrupt.

Revert the order so we get the next tick interrupt in the future.

Fixes: commit 0ff53d096422 "tick: sched: Force tick interrupt and get rid of softirq magic"
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1453893967-3458-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 kernel/time/tick-sched.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index c792429..3d31be1 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -988,9 +988,9 @@ static void tick_nohz_switch_to_nohz(void)
 	/* Get the next period */
 	next = tick_init_jiffy_update();
 
-	hrtimer_forward_now(&ts->sched_timer, tick_period);
 	hrtimer_set_expires(&ts->sched_timer, next);
-	tick_program_event(next, 1);
+	hrtimer_forward_now(&ts->sched_timer, tick_period);
+	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
 	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
 }
 
-- 
1.9.1

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