linux-kernel - Re: [PATCH 2/4] sched: implement __set_cpus

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Message-ID: <4C038A08.8090209@kernel.org>
Date:	Mon, 31 May 2010 12:06:00 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Galbraith <efault@....de>
Subject: Re: [PATCH 2/4] sched: implement __set_cpus_allowed()

On 05/31/2010 12:02 PM, Peter Zijlstra wrote:
> On Mon, 2010-05-31 at 12:01 +0200, Peter Zijlstra wrote:
>>>  but we can update cpu_active mask before other
>>> CPU_UP_PREPARE notifiers are executed so that it's symmetrical to cpu
>>> down path and then this problem goes away the exact same way, right?
>>
>> Ah, no, we cannot mark it active before its actually up, because at that
>> time we'll actually try and run stuff on it, which clearly won't work
>> when its not there to run stuff. 
> 
> So we should clear it _before_ we go down, and set it _after_ we're up.
> 

Yeah, sure, I misspoke.  I meant CPU_ONLINE not CPU_UP_PREPARE.  So,
we can mark a cpu active before other CPU_ONLINE callbacks are run.

Thanks.

-- 
tejun
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