linux-kernel - Re: [RFC] cpuset: remove sched domain hooks from cpusets

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Message-ID: <4538F34A.7070703@yahoo.com.au>
Date:	Sat, 21 Oct 2006 02:03:22 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Martin Bligh <mbligh@...gle.com>
CC:	Paul Jackson <pj@....com>, akpm@...l.org, menage@...gle.com,
	Simon.Derr@...l.net, linux-kernel@...r.kernel.org, dino@...ibm.com,
	rohitseth@...gle.com, holt@....com, dipankar@...ibm.com,
	suresh.b.siddha@...el.com
Subject: Re: [RFC] cpuset: remove sched domain hooks from cpusets

Martin Bligh wrote:
> 
>> I don't know of anyone else using cpusets, but I'd be interested to know.
> 
> 
> We (Google) are planning to use it to do some partitioning, albeit on
> much smaller machines. I'd really like to NOT use cpus_allowed from
> previous experience - if we can get it to to partition using separated
> sched domains, that would be much better.
> 
>  From my dim recollections of previous discussions when cpusets was
> added in the first place, we asked for exactly the same thing then.
> I think some of the problem came from the fact that "exclusive"
> to cpusets doesn't actually mean exclusive at all, and they're
> shared in some fashion. Perhaps that issue is cleared up now?
> /me crosses all fingers and toes and prays really hard.

The I believe, is that an exclusive cpuset can have an exclusive parent
and exclusive children, which obviously all overlap one another, and
thus you have to do the partition only at the top-most exclusive cpuset.

Currently, cpusets is creating partitions in cpus_exclusive children as
well, which breaks balancing for the parent.

The patch I posted previously should (modulo bugs) only do partitioning
in the top-most cpuset. I still need clarification from Paul as to why
this is unacceptable, though.

-- 
SUSE Labs, Novell Inc.
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