linux-kernel - [tip:timers/urgent] tick/nohz: Set the correct expiry when switching to nohz/lowres mode

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Message-ID: <tip-1ca8ec532fc2d986f1f4a319857bb18e0c9739b4@git.kernel.org>
Date:	Wed, 27 Jan 2016 03:48:33 -0800
From:	tip-bot for Wanpeng Li <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	fweisbec@...il.com, tglx@...utronix.de, wanpeng.li@...mail.com,
	kernellwp@...il.com, peterz@...radead.org, hpa@...or.com,
	linux-kernel@...r.kernel.org, mingo@...nel.org
Subject: [tip:timers/urgent] tick/nohz:
  Set the correct expiry when switching to nohz/lowres mode

Commit-ID:  1ca8ec532fc2d986f1f4a319857bb18e0c9739b4
Gitweb:     http://git.kernel.org/tip/1ca8ec532fc2d986f1f4a319857bb18e0c9739b4
Author:     Wanpeng Li <kernellwp@...il.com>
AuthorDate: Wed, 27 Jan 2016 19:26:07 +0800
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 27 Jan 2016 12:45:57 +0100

tick/nohz: Set the correct expiry when switching to nohz/lowres mode

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@...mail.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/1453893967-3458-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 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 cbe5d8d..de2d9fe 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -995,9 +995,9 @@ 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);
 }