linux-kernel - Re: [PATCH] sched_rt: Removes extra checking for nr_cpus_allowed when calling find_lowest

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Message-ID: <1287486167.1994.1.camel@twins>
Date:	Tue, 19 Oct 2010 13:02:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: Re: [PATCH] sched_rt: Removes extra checking for nr_cpus_allowed
 when calling find_lowest_rq

On Tue, 2010-10-19 at 16:57 +0600, Rakib Mullick wrote:
> sched_rt: Removes extra checking for nr_cpus_allowed when calling
> find_lowest_rq

Why repeat this subject?

> Remove the check for nr_cpus_allowed of an RT task before calling
> find_lowest_cpu() from select_task_rq_rt function. Cause
> find_lowest_cpu checks for rt.nr_cpus_allowed of a process.
> It would've been nice, if we make the check before calling
> find_lowest_cpu. But its called from other places, so keep the
> nr_cpus_allowed check into find_lowest_cpu().

That's just not explaining anything.. what can go wrong, how does this
fix it.

> Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
> ---
> 
> --- linus-rc8/kernel/sched_rt.c	2010-10-15 05:26:43.000000000 +0600
> +++ rakib-rc8/kernel/sched_rt.c	2010-10-19 16:22:30.000000000 +0600
> @@ -971,8 +971,7 @@ select_task_rq_rt(struct rq *rq, struct
>  	 * that is just being woken and probably will have
>  	 * cold cache anyway.
>  	 */
> -	if (unlikely(rt_task(rq->curr)) &&
> -	    (p->rt.nr_cpus_allowed > 1)) {
> +	if (unlikely(rt_task(rq->curr))) {
>  		int cpu = find_lowest_rq(p);
> 
>  		return (cpu == -1) ? task_cpu(p) : cpu;

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