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

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Date:	Sat, 21 Oct 2006 00:52:50 +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

Nick Piggin wrote:

> set_cpus_allowed is a feature of the scheduler that allows you to
> restrict one task to a subset of all cpus. Right?
> 
> And cpusets uses this interface as the mechanism to implement the
> semantics which the user has asked for. Yes?
> 
> sched-domains partitioning is a feature of the scheduler that
> allows you to restrict zero or more tasks to the partition, and
> zero or more tasks to the complement of the partition. OK?
> 
> So if you have a particular policy you need to implement, which is
> one cpus_exclusive cpuset off the root, covering half the cpus in
> the system (as a simple example)... why is it good to implement
> that with set_cpus_allowed and bad to implement it with partitions?
> 
> Or, another question, how does my patch hijack cpus_allowed? In
> what way does it change the semantics of cpus_allowed?

That should be, in what way does it change the semantics of cpusets
in any way?

IOW, how could a user possibly notice or care that partitions are
being used to implement a given policy? (apart from the fact that
the balancing will work better).

-- 
SUSE Labs, Novell Inc.
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