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

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Message-Id: <1212605794.19205.19.camel@lappy.programming.kicks-ass.net>
Date:	Wed, 04 Jun 2008 20:56:34 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Max Krasnyansky <maxk@...lcomm.com>
Cc:	Paul Jackson <pj@....com>, Andi Kleen <andi@...stfloor.org>,
	ioe-lkml@...eria.de, sivanich@....com,
	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)

On Wed, 2008-06-04 at 11:29 -0700, Max Krasnyansky wrote:
> 
> 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.

The advantage of using a replacement /sbin/init is that you execute
before the rest of userspace, unlike what you propose.

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