linux-kernel - Re: [RFC PATCH v2] sched/deadline: support dl task migration during cpu hotplug

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Message-ID: <20141106014634.GA25640@kernel>
Date:	Thu, 6 Nov 2014 09:46:34 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Wanpeng Li <kernellwp@...il.com>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@....com>,
	Kirill Tkhai <ktkhai@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2] sched/deadline: support dl task migration during
 cpu hotplug

Hi Peter,
On Wed, Nov 05, 2014 at 01:52:54PM +0100, Peter Zijlstra wrote:
>On Wed, Nov 05, 2014 at 06:59:35PM +0800, Wanpeng Li wrote:
>> Hi Peter,
>> On 14/11/5 下午6:50, Peter Zijlstra wrote:
>> >On Wed, Nov 05, 2014 at 04:51:57PM +0800, Wanpeng Li wrote:
>> >>Note: dl task can be migrated successfully if rq is offline currently, however,
>> >>I'm still not sure why task_rq(task)->rd->span just include the cpu which the dl
>> >>task previous running on, so cpu_active_mask is used in the patch.
>> >>
>> >>Peterz, Juri?
>> >So the root domain span is for exclusive cpusets
>> >(Documentation/cgroups/cpusets.txt) where we fully separate sets of CPUs
>> >and have no load-balancing between the sets.
>> >
>> >For 'normal' setups the rd->span is the entire machine, but using
>> >cpusets you can create more (smaller) domains.
>> 
>> I don't setup any cpusets related stuff, however, task_rq(task)->rd->span
>> just include the cpu which the dl task previous running on instead of the
>> entire machine in find_later_rq().
>
>Ah, it could be that for offline cpus we have a singleton rd. Lemme try

I still cannot find where build the singleton rd in the codes, could you
point out?

Regards,
Wanpeng Li

>and remember wth we did there.

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