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

[Wanpeng Li <kernellwp@gmail.com>]

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