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

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Message-ID: <1338932241.2749.62.camel@twins>
Date:	Tue, 05 Jun 2012 23:37:21 +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 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'?

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.

If you don't bring them down far enough to unplug, should you still be
calling it hotplug?

Ideally I think there'd be a file in your cpuset which if opened and
written to will flush all pending bits (timers, workqueues, the lot) and
return when this is done (and maybe provide O_ASYNC writes to not wait
for completion).

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