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

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Date:	Wed, 04 Jun 2008 10:47:58 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Ingo Oeser <ioe-lkml@...eria.de>
CC:	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>,
	Nick Piggin <nickpiggin@...oo.com.au>, 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)

Ingo Oeser wrote:
> Hi Max,
> 
> On Wednesday 04 June 2008, Max Krasnyanskiy wrote:
>> btw Ingo, I just realized that maxcpu= option is exactly what you need.
>> Here is how you can use it.
>> Boot your system with maxcpus=1. That way the kernel will only bring up 
>> processor 0. I'm assuming cpu0 is "good" otherwise your system is totally 
>> busted :). Other cpus will stay off-line and will not be initialized.
>> Then once the system boots you can selectively bring "good" processors online 
>> by doing
>> 	echo 1 > /sys/devices/system/cpu/cpuN/online
>>
> 
> I just tested it on the Ubuntu Hardy standard kernel on an AMD DualCore.
> The /sys/devices/system/cpu/cpu1 entry doesn't show up.
> 
> I can send you the dmesg/config in private, if you want.
> 
> Did you test your suggestion? 
No, I just give random suggestions without verifying them first ;-).
Of course I tried it. Sounds like your Ubuntu kernel does not have "CPU
hotplug / suspend on SMP" enabled. I thought that all distributions enable it
by default these days.

Max
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