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Subject: Re: [PATCH 2/4] sched: adjust when cpu_active and cpuset
 configurations are updated during cpu on/offlining
From: Peter Zijlstra <peterz@infradead.org>
To: Tejun Heo <tj@kernel.org>
Cc: mingo@elte.hu, linux-kernel@vger.kernel.org, rusty@rustcorp.com.au,
       paulus@samba.org, acme@redhat.com, Paul Menage <menage@google.com>
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Date: Tue, 01 Jun 2010 19:20:35 +0200
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On Tue, 2010-06-01 at 18:58 +0200, Tejun Heo wrote:
> Hello,
> 
> On 06/01/2010 05:57 PM, Peter Zijlstra wrote:
> > I know we all love notifier lists, but doesn't the below code get lots
> > more readable if we don't play tricks with notifier priorities and
> > simply hardcode the few (perf/sched/cpuset) callbacks into the hotplug
> > paths?
> 
> Maybe, maybe not.  In this case, I kind of like that sleep failure
> case doesn't have to be explicitly rolled back but if you like hard
> coding that's fine too.

Hurm, yeah that rollback might make things messy indeed.

> > Also, I'm afraid you've now inverted the relation between
> > cpu_active_mask and parition_sched_domains().
> >
> > You need to first set/clear the active mask, then rebuild the domain.
> > But with your patch parition_sched_domains() gets called in the regular
> > DOWN_PREPARE path, while we only clear active at the very end, which
> > means we build the wrong domains.
> 
> Ah, right forgot about that.  So, the things that need to be ordered
> are cpu_active mask update, cpuset configuration and sched domains,
> right?

Right, I think that should cover it.