linux-kernel - Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may have realtime uses)

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Message-ID: <20080604200350.GL20824@one.firstfloor.org>
Date:	Wed, 4 Jun 2008 22:03:50 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Paul Jackson <pj@....com>
Cc:	Andi Kleen <andi@...stfloor.org>, maxk@...lcomm.com,
	ioe-lkml@...eria.de, sivanich@....com, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, kernel@...ivas.org, dfults@....com,
	devik@....cz, dino@...ibm.com, emmanuel.pacaud@...v-poitiers.fr,
	deweerdt@...e.fr, mingo@...e.hu, colpatch@...ibm.com,
	nickpiggin@...oo.com.au, rostedt@...dmis.org, oleg@...sign.ru,
	paulmck@...ibm.com, menage@...gle.com, rddunlap@...l.org,
	suresh.b.siddha@...el.com, tglx@...utronix.de
Subject: Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may have realtime uses)

> We (SGI) routinely handle that need with a custom init program,
> invoked with the init= parameter to the booting kernel, which
> sets up cpusets and then invokes the normal (real) init program
> in a cpuset configured to exclude those CPUs and nodes which we
> want to remain unloaded.  For example, on a 256 CPU, 64 node
> system, we might have init running on a single node of 4 CPUs,
> and leave the remaining 63 nodes and 252 CPUs isolated from all
> the usual user level daemons started by init.
> 
> There is no need for additional kernel changes to accomplish this.

There are no additional changes needed, but you must admit that isolcpus
is a much more elegant solutation for this problem than hijacking init.

-Andi
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