Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752483AbZFQPH6 (ORCPT ); Wed, 17 Jun 2009 11:07:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751857AbZFQPHu (ORCPT ); Wed, 17 Jun 2009 11:07:50 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:58054 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751656AbZFQPHt (ORCPT ); Wed, 17 Jun 2009 11:07:49 -0400 Date: Wed, 17 Jun 2009 17:07:00 +0200 From: Ingo Molnar To: "Paul E. McKenney" Cc: Peter Zijlstra , svaidy@linux.vnet.ibm.com, Andrew Morton , Gautham R Shenoy , linux-kernel@vger.kernel.org, Balbir Singh , Rusty Russel , Nathan Lynch , Venkatesh Pallipadi , Dipankar Sarma , Shoahua Li Subject: Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support. Message-ID: <20090617150700.GB20345@elte.hu> References: <20090616053431.30891.18682.stgit@sofia.in.ibm.com> <20090615232318.74b099a6.akpm@linux-foundation.org> <20090616080715.GB7961@dirshya.in.ibm.com> <1245223977.13761.21576.camel@twins> <20090617143804.GA6767@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090617143804.GA6767@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2008 Lines: 51 * Paul E. McKenney wrote: > On Wed, Jun 17, 2009 at 09:32:57AM +0200, Peter Zijlstra wrote: > > On Tue, 2009-06-16 at 13:37 +0530, Vaidyanathan Srinivasan wrote: > > > * Andrew Morton [2009-06-15 23:23:18]: > > > > > > > On Tue, 16 Jun 2009 11:08:39 +0530 Gautham R Shenoy wrote: > > > > > > > > > Currently on a ppc64 box with 16 CPUs, the time taken for > > > > > a individual cpu-hotplug operation is as follows. > > > > > > > > > > # time echo 0 > /sys/devices/system/cpu/cpu2/online > > > > > real 0m0.025s > > > > > user 0m0.000s > > > > > sys 0m0.002s > > > > > > > > > > # time echo 1 > /sys/devices/system/cpu/cpu2/online > > > > > real 0m0.021s > > > > > user 0m0.000s > > > > > sys 0m0.000s > > > > > > > > Surprised. Do people really online and offline CPUs frequently enough > > > > for this to be a problem? > > > > > > Certainly not for hardware faults or hardware replacement, but > > > cpu-hotplug interface is useful for changing system configuration to > > > meet different objectives like > > > > > > * Reduce system capacity to reduce average power and reduce heat > > > > > > * Increasing number of cores and threads in a CPU package is leading > > > to multiple cpu offline/online operations for any perceivable effect > > > > > > * Dynamically change CPU configurations in virtualized environments > > > > I tend to agree with Andrew, if any of those things are done > > frequent enough that the hotplug performance matter you're doing > > something mighty odd. > > Boot speedup? Also, if it brings more attention (and more stability and more bugfixes) to CPU hotplug that's only good. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/