linux-kernel - Re: [PATCH 06/16] sched: SCHED

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Date:	Wed, 11 Apr 2012 12:21:38 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Juri Lelli <juri.lelli@...il.com>
Cc:	peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
	oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
	johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fchecconi@...il.com,
	tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
	luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com
Subject: Re: [PATCH 06/16] sched: SCHED_DEADLINE push and pull logic

On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote:

>  /*
>   * Only called when both the current and waking task are -deadline
>   * tasks.
> @@ -487,8 +819,20 @@ static void yield_task_dl(struct rq *rq)
>  static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
>  				  int flags)
>  {
> -	if (dl_time_before(p->dl.deadline, rq->curr->dl.deadline))
> +	if (dl_time_before(p->dl.deadline, rq->curr->dl.deadline)) {
>  		resched_task(rq->curr);
> +		return;
> +	}
> +
> +#ifdef CONFIG_SMP
> +	/*
> +	 * In the unlikely case current and p have the same deadline
> +	 * let us try to decide what's the best thing to do...
> +	 */
> +	if ((s64)(p->dl.deadline - rq->curr->dl.deadline) == 0 &&
> +	    !need_resched())

OK, maybe I'm thick. But how is:

  (s64)(p->dl.deadline - rq->curr->dl.deadline) == 0

Better than:

  p->dl.deadline == rq->curr->dl.deadline

?

-- Steve

> +		check_preempt_equal_dl(rq, p);
> +#endif /* CONFIG_SMP */
>  }
>  


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