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

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Message-Id: <1212446707.6269.26.camel@lappy.programming.kicks-ass.net>
Date:	Tue, 03 Jun 2008 00:45:07 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Oeser <ioe-lkml@...eria.de>
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>,
	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>,
	"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)

On Tue, 2008-06-03 at 00:35 +0200, Ingo Oeser wrote:
> 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.

Yeah - except that its not meant to be used as such - it will still
brings the cpu up, and it is still usable for the OS.

So sorry, your abuse doesn't make for a case to keep this abomination.

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