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

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Message-Id: <200806030035.58387.ioe-lkml@rameria.de>
Date:	Tue, 3 Jun 2008 00:35:55 +0200
From:	Ingo Oeser <ioe-lkml@...eria.de>
To:	Paul Jackson <pj@....com>
Cc:	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>,
	Max Krasnyansky <maxk@...lcomm.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>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"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 Paul,

in short: NAK!

On Monday 02 June 2008, Paul Jackson wrote:
> (Aside to the RealTime folks -- is there a 'realtime'
> email list which I should include in this discussion?)
> 
> The kernel has a "isolcpus=" kernel boot time parameter.  This
> parameter isolates CPUs from scheduler load balancing, minimizing the
> impact of scheduler latencies on realtime tasks running on those CPUs.

I used it to mask out a defect CPU on a 8-CPU node of a 
HPC-cluster at a customer site, until the $BIG_VENDOR 
sent a replacement. And to prove $BIG_VENDOR, that we actually
have a problem on THAT CPU.

So I would really like to keep this fault isolation capability.
I made my customer happy with that.

I wish Linux had more such "mask out bad hardware" features
to faciliate fault isolation and boot and runtime.


Best Regards

Ingo Oeser
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