linux-kernel - Re: [PATCH] cpuset and sched domains: sched_load

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Message-Id: <20071001111528.5487b4f4.pj@sgi.com>
Date:	Mon, 1 Oct 2007 11:15:28 -0700
From:	Paul Jackson <pj@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	akpm@...ux-foundation.org, menage@...gle.com,
	linux-kernel@...r.kernel.org, dino@...ibm.com, cpw@....com,
	mingo@...e.hu
Subject: Re: [PATCH] cpuset and sched domains: sched_load_balance flag

Nick wrote:
> which you could equally achieve by adding
> a second set of sched domains (and the global domains could keep
> globally balancing).

Hmmm ... this could be the key to this discussion.

Nick - can two sched domains overlap?  And if they do, what does that
mean on any user or application behaviour.

>From the cpuset side - this patch handles overlap by joining the 'cpus'
into one sched domain.  If two cpusets with overlapping 'cpus' are both
marked 'sched_load_balance', then this patch forms a single, combined
sched domain.

As best as I can tell, you and I are actually in agreement in the
case that there is no overlap.  If the several cpusets which have
'sched_load_balance' enabled have mutually disjoint 'cpus' (no
overlap), then my patch forms exactly one sched domain for each such
cpuset, having the same 'cpus'.

The issue is the overlapping cases - are overlapping sched domains
allowed, and if so, how do they affect user space?

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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