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

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Date:	Tue, 03 Jun 2008 20:00:12 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Ingo Oeser <ioe-lkml@...eria.de>,
	Dimitri Sivanich <sivanich@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org,
	Con Kolivas <kernel@...ivas.org>,
	"Derek L. Fults" <dfults@....com>, devik <devik@....cz>,
	Dinakar Guniguntala <dino@...ibm.com>,
	Emmanuel Pacaud <emmanuel.pacaud@...v-poitiers.fr>,
	Frederik Deweerdt <deweerdt@...e.fr>,
	Ingo Molnar <mingo@...e.hu>,
	Matthew Dobson <colpatch@...ibm.com>, rostedt@...dmis.org,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Paul Menage <menage@...gle.com>,
	"Randy.Dunlap" <rddunlap@...l.org>, suresh.b.siddha@...el.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may
 have realtime uses)



Nick Piggin wrote:
> On Wednesday 04 June 2008 09:47, Max Krasnyanskiy wrote:
 >> Dimitri, you can probably use that too. ie Boot the thing with most CPUs
>> offline and then bring them online. That way you'll know for sure that no
>> timers, works, hard-/soft-irqs, etc are running on them.
> 
> When you bring a CPU online, in theory the sched domains should get
> set up for them, so you should start seeing processes get migrated
> onto it, and with them timers work queues etc.
> 
> If you have irqbalanced running, it probably migrates irqs onto them
> as well if it needs to.

Sure. My suggestion assumes that system wide balancing is disabled (via top
level cpuset) and that IRQ affinity masks are properly setup. I mentioned that
in my earlier emails.

Max
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