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

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Date:   Thu, 9 Aug 2018 12:45:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Leo Yan <leo.yan@...aro.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 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().

>  			tick_nohz_idle_retain_tick();
> +		}
>  

However, I would rather we stuff all this into retain_tick.