linux-kernel - Re: [PATCH 4/7] sched: implement force_cpus

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Message-ID: <4B1E1130.9050108@kernel.org>
Date:	Tue, 08 Dec 2009 17:41:20 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...e.hu, avi@...hat.com, efault@....de,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	Gautham R Shenoy <ego@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4/7] sched: implement force_cpus_allowed()

Hello,

On 12/07/2009 08:07 PM, Tejun Heo wrote:
> On 12/07/2009 07:54 PM, Peter Zijlstra wrote:
>> So we seem to do cleanup_workqueue_thread() from CPU_POST_DEAD, but at
>> that time any thread that might still be around will most certainly not
>> be running on the offlined cpu anymore.
>>
>> If you really want to ensure you remain on the cpu, you have to complete
>> from CPU_DOWN_PREPARE.
>>
>> We're not running things from offline CPUs.
> 
> Oh, no, we're not doing that.  We can't do that.  What we're doing is
> to continue to process works which were queued on the now offline cpu
> unless it has been flushed/cancled from one of the cpu down
> notifications and the reason why we need to be able to fork after
> active is clear is to guarantee those flush/cancels don't deadlock.

Does my explanation justify the patch?

Thanks.

-- 
tejun
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