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

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Message-ID: <3908561D78D1C84285E8C5FCA982C28F19300965@ORSMSX104.amr.corp.intel.com>
Date:	Tue, 5 Jun 2012 17:44:11 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>
CC:	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

> Like what? Offline is nothing more than a C state on x86. 

Offline is a bigger hammer than idle.

When a core is idle it may take an interrupt which wakes it up to use power.
The scheduler may assign a process to run on it, which will wake it up to use power.

When a core is offline we take extra steps (re-routing interrupts, telling the
scheduler it is not available for work) to make sure it STAYS in that low
power state.

-Tony
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