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

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Date:	Wed, 06 Jun 2012 14:17:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	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 15:00 -0700, Paul E. McKenney wrote:
> On Tue, Jun 05, 2012 at 11:37:21PM +0200, Peter Zijlstra wrote:
> > On Tue, 2012-06-05 at 14:29 -0700, Paul E. McKenney wrote:
> > > OK, I'll bite...  Why not just use CPU hotplug to expel the timers?
> > 
> > Currently? Can you say: 'kstopmachine'?
> 
> So if CPU hotplug (or whatever you want to call it) stops using
> kstopmachine, you are OK with it?

It would be much better, still not ideal though.

> > But its also a question of interface and naming. Do you want to have to
> > iterate all cpus in your isolated set, do you want to bring them down
> > far enough to physically unplug. Ideally no to both.
> 
> For many use cases, it is indeed not necessary to get to a point where
> the CPUs could be physically removed from the system.  But CPU-failure
> use cases would need the CPU to be fully deactivated.  And many of the
> hardware guys tell me that the CPU-failure case will be getting more
> common, though I sure hope that they are wrong.

Uhm, yeah, that doesn't sound right.

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