linux-kernel - RE: [PATCH v4 0/7] x86: BSP or CPU0 online/offline

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Date:	Tue, 6 Dec 2011 16:15:31 -0800
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Borislav Petkov <bp@...64.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	Ingo Molnar <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	"Herrmann3, Andreas" <Andreas.Herrmann3@....com>
Subject: RE: [PATCH v4 0/7] x86: BSP or CPU0 online/offline


> From: Borislav Petkov [mailto:bp@...64.org]
> On Tue, Dec 06, 2011 at 04:55:02PM +0530, Srivatsa S. Bhat wrote:
> > By the way, this problem is not tied to CPU0 alone, it exists for any
> > CPU! (as long as we are talking about plugging in/out CPUs
> physically).
> 
> Just a reminder: before you guys go and wander off into the woods of
> hypothetical with this, please make sure this use case is relevant
> enough for the trouble. The only real reason given so far AFAICT was
> RAS
> and to be able to offline BSP in order to prolong system life before
> maintenance.
> 
> When you take it down for maintenance eventually, you don't need to
> suspend but simply poweroff.

Agree with you. To maintain a system with a bad CPU, either you hot plug or hot replace the CPU, or you power off then replace the CPU. Replacing the CPU between suspend and resume doesn't seem a normal RAS behavior.

If you choose hotplug or hot replace the CPU, then this patchset is useful.

CPU0 offline/online is a must-have if you want to replace a socket which has the BSP in it for any errors in uncore or a sibling CPU. Not mention that CPU0 itself is bad and you want to hot unplug it.

Thanks.

-Fenghua
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