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Message-ID: <4538E2C2.8060307@yahoo.com.au>
Date: Sat, 21 Oct 2006 00:52:50 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Paul Jackson <pj@sgi.com>
CC: akpm@osdl.org, mbligh@google.com, menage@google.com, Simon.Derr@bull.net,
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       holt@sgi.com, dipankar@in.ibm.com, suresh.b.siddha@intel.com,
       clameter@sgi.com
Subject: Re: [RFC] cpuset: add interface to isolated cpus
References: <20061019092607.17547.68979.sendpatchset@sam.engr.sgi.com>	<453750AA.1050803@yahoo.com.au>	<20061019105515.080675fb.pj@sgi.com>	<4537BEDA.8030005@yahoo.com.au>	<20061019115652.562054ca.pj@sgi.com>	<4537CC1E.60204@yahoo.com.au> <20061019203744.09b8c800.pj@sgi.com> <453882AC.3070500@yahoo.com.au>
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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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