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

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Message-ID: <4846DF25.4020300@qualcomm.com>
Date:	Wed, 04 Jun 2008 11:29:57 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Paul Jackson <pj@....com>
CC:	Andi Kleen <andi@...stfloor.org>, 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)



Paul Jackson wrote:
> Andi wrote:
>> Right now the system boot could put pages from some daemon in there before any 
>> cpusets are set up and there's no easy way to get them away again
> 
> 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.

You do not even need to replace /sbin/init for this, no ?
Simply installing custom
	/etc/init.d/create_cpusets
with priority 0
	# chkconfig: 12345 0 99
will do the job.

That script will move init itself into the appropriate cpuset and from then on
everything will inherit it.

Max
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