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

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Message-ID: <545B5C07.6050400@gmail.com>
Date:	Thu, 06 Nov 2014 19:31:19 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	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


On 14/11/6 下午6:08, Peter Zijlstra wrote:
> On Thu, Nov 06, 2014 at 09:46:34AM +0800, Wanpeng Li wrote:
>
>>> 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?
> So this is all quite horrible code, but what I think happens is that:
>
> 	sched_cpu_inactive() -> set_cpu_active(cpu, false);
> 	cpuset_cpu_inactive() -> cpuset_update_active_cpus(false)
> 	                      -> partition_sched_domains(1, NULL, NULL)
> 			      -> build_sched_domains(cpu_active_mask)
> 			      -> for_each_cpu()
> 			           cpu_attach_domain() -> rq_attach_root()
>
> Now, that will detach all active cpus from the current root domain and
> attach them to the new root domain. Which leaves behind the old root
> domain attached to only the one 'dead' cpu.

Got it, thanks for your great explanation. ;-)

Regards,
Wanpeng Li


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