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

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Message-ID: <BANLkTinzsjTy6yA7N-ssy5beyJn5NQZX3w@mail.gmail.com>
Date:	Wed, 18 May 2011 22:46:19 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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, May 18, 2011 at 9:24 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 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?
>
Hi Steven

For migration, it is the case that cpu != rq->cpu, and
if cpu is allowed by task's affinity, it is bug that task
could not goto cpu because of nr_cpus_allowed since
the nr_cpus_allowed is computed based on the cpus_allowed mask.

Hillf
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