linux-kernel - Re: [RFC] cpuset: add interface to isolated cpus

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Message-ID: <4539FB9C.10204@yahoo.com.au>
Date:	Sat, 21 Oct 2006 20:51:08 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Paul Jackson <pj@....com>
CC:	akpm@...l.org, mbligh@...gle.com, 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, clameter@....com
Subject: Re: [RFC] cpuset: add interface to isolated cpus

Paul Jackson wrote:
>>If you always have other domains overlapping them (regardless
>>that it is a parent), then what actual use does cpu_exclusive
>>flag have?
> 
> 
> Good question.  To be a tad too honest, I don't consider it to be
> all that essential.
> 
> It does turn out to be a bit useful, in that you can be confident that
> if you are administering the batch scheduler and it has a cpu_exclusive
> cpuset covering a big chunk of your system, then no other cpuset other
> than the top cpuset right above, which you administer pretty tightly,
> could have anything overlapping it.  You don't have to actually look
> at the cpumasks in all the parallel cpusets and cross check each one
> against the batch schedulers set of cpus for overlap.
> 
> But as you can see by grep'ing in kernel/cpuset.c, it is only used
> to generate a couple of error returns, for things that you can do
> just fine by turning off the cpu_exclusive flag.

Well, it was supposed to be used for sched-domains partitioning, and
its uselessness for anything else I guess is what threw me.

But even the way cpu_exclusive semantics are defined makes it not
quite compatible with partitioning anyway, unfortunately.

-- 
SUSE Labs, Novell Inc.
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