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

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Message-ID: <3908561D78D1C84285E8C5FCA982C28F19301A16@ORSMSX104.amr.corp.intel.com>
Date:	Tue, 5 Jun 2012 19:54:19 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
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

> But given that you care about how fast a cpu can come up again, this
> seems to be exactly what you want. You want to adapt to load fast, so
> why bother going through userspace and wrecking bits in between?

There are multiple needs here - that appear to have some significant
overlap (re-routing interrupts, stopping scheduling).

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).

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

-Tony
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