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@hotmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1453893967-3458-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index cbe5d8dcf15a52b6ff62c5d273fd82330c5b80b8..de2d9fef6ea60dcffe5d55cac0182b679c839ebd 100644 (file)
--- 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);
 }