linux-kernel - Re: [PATCH] cpuset: Rework sched domains and CPU hotplug handling (2.6.27-rc1)

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Date:	Tue, 05 Aug 2008 13:30:43 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Paul Jackson <pj@....com>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org, menage@...gle.com,
	a.p.zijlstra@...llo.nl, vegard.nossum@...il.com,
	lizf@...fujitsu.com
Subject: Re: [PATCH] cpuset: Rework sched domains and CPU hotplug handling
 (2.6.27-rc1)

Paul Jackson wrote:
> Max wrote:
>> Actually it is appropriate, and there is one more user of the
>> arch_reinit_sched_domains() which is S390 topology updates.
>> Those things (mc_power and topology updates) have to update domain flags based
>> on the mc/smt power and current topology settings.
> 
> Hmmm ... ok I suppose.
> 
> Could we have the kernel/sched.c code, in this case, call the
> kernel/cpuset.c routine async_rebuild_sched_domains(), rather
> than the synchronous rebuild_sched_domains() call (in your naming)
> which required details of the get_online_cpus() and put_online_cpus()
> wrapping to leak into kernel/sched.c:arch_reinit_sched_domains()
> routine?

It could I guess. But the questions is why ?
I mean the only reason we've introduced workqueue is because lock 
nesting got too complicated. Otherwise in all those paths we're already 
in a process context and there is no need to schedule a workqueue.

I see your point about get_online_cpus() thing. But it is similar to 
partition_sched_domains() which is an external (from the sched pov) 
interface and must be called within get_online_cpus() ... put_online_cpus().

Max


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