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

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Date:	Tue, 3 Jun 2008 01:55:57 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	Max Krasnyansky <maxk@...lcomm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Paul Jackson <pj@....com>, linux-kernel@...r.kernel.org,
	Con Kolivas <kernel@...ivas.org>,
	"Derek L. Fults" <dfults@....com>, devik <devik@....cz>,
	Dimitri Sivanich <sivanich@....com>,
	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)

Hi Max,
Hi Peter,

On Tuesday 03 June 2008, Max Krasnyansky wrote:
> Ingo, I just wanted to elaborate on what Peter is saying. That CPU will still
> have to be _booted_ properly. It may be used for hard- and soft- interrupt
> processing, workqueues (internal kernel queuing mechanism) and kernel timers.

Oh! Didn't know that user process scheduling is so much 
> In your particular case you're much much much better off with doing
> 	echo 0 > /sys/devices/system/cpuN/online
> either during initrd stage or as a first init script.
> That way bad cpu will be _completely_ disabled.

The initrd is from the distribution. I have no sane way to change it
fast and permanent. Can I change the initrd and still have a certified
RHEL or SLES? Are there initrd hooks, which survive packet installation?

I would really appreciate some way to keep the kernel from using 
a CPU at all to do fault isolation. If possible not even booting it.

Bootparameters survived all distro fiddling so far. I love them!

Try to convince a hardware vendor, that you don't have a software bug.
Try to convince him that you didn't break the hardware by swapping it around.

So I'll ACK removing isolcpus, if we get a better replacement boot option.


Best Regards

Ingo Oeser
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