linux-kernel - RE: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

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Date:	Tue, 05 Jun 2012 21:56:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>, linux-pm <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: RE: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or
 nmi

On Tue, 2012-06-05 at 19:54 +0000, Luck, Tony wrote:

> My need is for RAS reasons to take a cpu offline - and since
> it is broken, I'm not going to bring it back again (at least not anytime
> soon - perhaps a service engineer will drive by in a few hours, pull out
> the broken cpu, put in a new one, and then bring that online ... but
> saving a few milli-seconds in this use case it pointless).

Right, performance is completely irrelevant in this case. In fact, the
current code should work perfectly fine for you -- except for the whole
BSP nightmare x86 has.

> Other people want to do this for power saving. They probably do care
> how fast the processor can be brought back. 

They're bloody insane, or working with broken hardware.
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