linux-kernel - Re: [PATCH] sched: correct how RT task is picked

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Message-ID: <1305725044.26849.11.camel@gandalf.stny.rr.com>
Date:	Wed, 18 May 2011 09:24:04 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Yong Zhang <yong.zhang0@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH] sched: correct how RT task is picked

On Wed, 2011-05-18 at 21:19 +0800, Hillf Danton wrote:

> Hi all
> 
> The patch is prepared again, in which tests for both cpu and
> nr_cpus_allowed are dropped.
> 
> The reason to drop nr_cpus_allowed is to make sure that the
> returned value is correct for both case that cpu == rq->cpu and
> case that cpu != rq->cpu.

-ENOPARSE

Why would we pick a task that can't migrate?

-- Steve

> 
> thanks
> 
> Hillf
> ---
> 
> --- a/kernel/sched_rt.c	2011-04-27 11:48:50.000000000 +0800
> +++ b/kernel/sched_rt.c	2011-05-18 21:16:22.000000000 +0800
> @@ -1149,9 +1149,7 @@ static void deactivate_task(struct rq *r
> 
>  static int pick_rt_task(struct rq *rq, struct task_struct *p, int cpu)
>  {
> -	if (!task_running(rq, p) &&
> -	    (cpu < 0 || cpumask_test_cpu(cpu, &p->cpus_allowed)) &&
> -	    (p->rt.nr_cpus_allowed > 1))
> +	if (!task_running(rq, p) && cpumask_test_cpu(cpu, &p->cpus_allowed))
>  		return 1;
>  	return 0;
>  }


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