linux-kernel - Re: [PATCH RFC] sched/deadline: support dl task migrate during cpu hotplug

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Message-ID: <20141104082345.GA22062@kernel>
Date:	Tue, 4 Nov 2014 16:23:45 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Kirill Tkhai <ktkhai@...allels.com>,
	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] sched/deadline: support dl task migrate during cpu
 hotplug

Hi Peter,
On Tue, Nov 04, 2014 at 09:32:25AM +0100, Peter Zijlstra wrote:
>On Tue, Nov 04, 2014 at 07:57:48AM +0800, Wanpeng Li wrote:
>> On Mon, Nov 03, 2014 at 11:41:11AM +0100, Peter Zijlstra wrote:
>
>> >On Fri, Oct 31, 2014 at 03:28:17PM +0800, Wanpeng Li wrote:
>> >So what is wrong with making dl_task_timer() deal with it? The timer
>> >will still fire on the correct time, canceling it and or otherwise
>> >messing with the CBS is wrong. Once it fires, all we need to do is
>> >migrate it to another cpu (preferably one that is still online of course
>> >:-).
>
>> Do you mean what I need to do is push the task to another cpu in dl_task_timer() 
>> if rq is offline?
>
>That does indeed appear to be the sensible fix to me.
>
>> In addition, what will happen if dl task can't preempt on 
>> another cpu?
>
>So if we find that the rq the task was on is no longer available, we
>need to select a new rq, the 'right' rq would be the one running the
>latest deadline.
>
>If it cannot preempt the latest (running) deadline, it was not eligible
>for running in the first place so no worries, right?

I think this will lead to this deadline task cannot running on any rqs any more.
If my understanding is not right, when it will be picked?

Regards,
Wanpeng Li 
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