linux-kernel - Re: [RFC v2 3/7] Improve the tracking of active utilisation

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Message-ID: <20160405124242.GX3430@twins.programming.kicks-ass.net>
Date:	Tue, 5 Apr 2016 14:42:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Luca Abeni <luca.abeni@...tn.it>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>
Subject: Re: [RFC v2 3/7] Improve the tracking of active utilisation

On Fri, Apr 01, 2016 at 05:12:29PM +0200, Luca Abeni wrote:
> @@ -526,7 +575,18 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
>  	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
>  	struct rq *rq = rq_of_dl_rq(dl_rq);
>  
> -	add_running_bw(dl_se, dl_rq);
> +	/*
> +	 * If the "inactive timer" is still active, stop it and leave
> +	 * the active utilisation unchanged.
> +	 * Otherwise, increase the active utilisation.
> +	 * If the timer cannot be cancelled, inactive_task_timer() will
> +	 * find the task state as TASK_RUNNING, and will do nothing, so
> +	 * we are still safe.
> +	 */
> +	if (hrtimer_active(&dl_se->inactive_timer))
> +		hrtimer_try_to_cancel(&dl_se->inactive_timer);

_try_, what happens if that fails?

> +	else
> +		add_running_bw(dl_se, dl_rq);
>  
>  	if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
>  	    dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {