linux-kernel - [PATCH v2] nohz: fix setting next jiffies while switch to low-res nohz mode

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Date:	Wed, 27 Jan 2016 19:26:07 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH v2] nohz: fix setting next jiffies while switch to low-res nohz mode

After commit 0ff53d096422 ("tick: sched: Force tick interrupt and get rid
of softirq magic"), next expire time is overwritten by last_jiffies_update
while switch to low-res nohz mode which leads to wrong next jiffies. 
This patch fix it by adjusting the order of forward/set in order to program 
ce device the right expire time in the future.

Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
v1 -> v2:
 * correct patch description

 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 9d7a053..a126d16 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -993,9 +993,9 @@ 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