linux-kernel - Re: [PATCH] sched: idle: Reenable sched tick for cpuidle request

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Date:   Thu, 9 Aug 2018 19:17:26 +0800
From:   leo.yan@...aro.org
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: idle: Reenable sched tick for cpuidle request

On Thu, Aug 09, 2018 at 12:45:49PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 09, 2018 at 01:47:27PM +0800, Leo Yan wrote:
> > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> > index 1a3e9bd..802286e 100644
> > --- a/kernel/sched/idle.c
> > +++ b/kernel/sched/idle.c
> > @@ -190,10 +190,18 @@ static void cpuidle_idle_call(void)
> >  		 */
> >  		next_state = cpuidle_select(drv, dev, &stop_tick);
> >  
> > -		if (stop_tick)
> > +		if (stop_tick) {
> >  			tick_nohz_idle_stop_tick();
> > -		else
> > +		} else {
> > +			/*
> > +			 * The cpuidle framework says to not stop tick but
> > +			 * the tick has been stopped yet, so restart it.
> > +			 */
> > +			if (tick_nohz_tick_stopped())
> > +				tick_nohz_idle_restart_tick();
> > +
> 
> I suspect you want an 'else' here. restart_tick already calls
> timer_clear_idle().

No, from the testing I found must call retain_tick, otherwise the
kernel compliants the warning from tick_nohz_idle_exit() when exit
from idle state:

        WARN_ON_ONCE(ts->timer_expires_base);

> >  			tick_nohz_idle_retain_tick();
> > +		}
> >  
> 
> However, I would rather we stuff all this into retain_tick.

Ah, yes; I tested below change and it also have same improvement for
idle state with my preivous change; please review if it's okay?

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index da9455a..fd2bfad 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -962,6 +962,10 @@ void tick_nohz_idle_stop_tick(void)
 
 void tick_nohz_idle_retain_tick(void)
 {
+       /* Restart the tikc if it has been stopped yet. */
+       if (tick_nohz_tick_stopped())
+               tick_nohz_idle_restart_tick();
+
        tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched));
        /*
         * Undo the effect of get_next_timer_interrupt() called from

Thanks,
Leo Yan