linux-kernel - Re: [PATCH] cpuset: Make rebuild_sched

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Message-Id: <20080715110726.5837c783.pj@sgi.com>
Date:	Tue, 15 Jul 2008 11:07:26 -0500
From:	Paul Jackson <pj@....com>
To:	Max Krasnyansky <maxk@...lcomm.com>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, maxk@...lcomm.com,
	a.p.zijlstra@...llo.nl, menage@...gle.com
Subject: Re: [PATCH] cpuset: Make rebuild_sched_domains() usable from any
 context

Max K wrote:
> Basically as Paul J. pointed out rebuild_sched_domains() is the
> only way to rebuild sched domains correctly based on the current
> cpuset settings. What this means is that we need to be able to
> call it from different contexts, like cpuhotplug for example.

The following is just a wild idea.

On systems using cpusets to setup scheduler domains (anything more
elaborate than the default of a single, system-wide, domain) have a
special purpose thread sit around, that does nothing except rebuild
sched domains on demand.

If this rebuild thread was the -only- way that sched domains were
allowed to be rebuilt, and if this rebuild was done -asynchronously-
sometime shortly after requested, without any error or status feedback,
then it would seem to simplify the locking issues.

I would guess that any system big enough to have a non-default, cpuset
determined, sched domain configuration is big enough to not mind one
more thread sitting around, doing nothing most of the time.

If the above is a really stupid idea, have fun taking out your
agression on it ;).

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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