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

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Date:	Tue, 5 Jun 2012 16:18:35 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
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>,
	"Luck, Tony" <tony.luck@...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

> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Tuesday, June 05, 2012 9:09 AM
> To: Yu, Fenghua
> Cc: Rusty Russell; Thomas Gleixner; Ingo Molnar; H Peter Anvin; Siddha,
> Suresh B; Luck, Tony; Mallick, Asit K; Arjan Dan De Ven; linux-kernel;
> x86; linux-pm; Srivatsa S. Bhat
> Subject: RE: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait
> or nmi
> 
> On Tue, 2012-06-05 at 16:02 +0000, Yu, Fenghua wrote:
> >
> > Users can consolidate processes on a few online CPU's and offline the
> > rest when workload is light.
> 
> No they can't, hotplug is a root only op.

That's right. A root admin does this. Actually some Linux people are adjusting online/offline CPU's based on workload to save power in their business. There are some advantages for online/offline CPU's than idling CPU's.

> 
> > This consolidation can save more power and have better performance
> > than idling CPU's because hot cache in online CPU's and offline CPU's
> > can be allocated in same package.
> 
> Yeah, or you fix the load-balancer to do this.

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