Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762942AbZFQHdG (ORCPT ); Wed, 17 Jun 2009 03:33:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753345AbZFQHc4 (ORCPT ); Wed, 17 Jun 2009 03:32:56 -0400 Received: from viefep19-int.chello.at ([62.179.121.39]:22612 "EHLO viefep19-int.chello.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753138AbZFQHcz (ORCPT ); Wed, 17 Jun 2009 03:32:55 -0400 X-SourceIP: 213.93.53.227 Subject: Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support. From: Peter Zijlstra To: svaidy@linux.vnet.ibm.com Cc: Andrew Morton , Gautham R Shenoy , linux-kernel@vger.kernel.org, Balbir Singh , Rusty Russel , Paul E McKenney , Nathan Lynch , Ingo Molnar , Venkatesh Pallipadi , Dipankar Sarma , Shoahua Li In-Reply-To: <20090616080715.GB7961@dirshya.in.ibm.com> References: <20090616053431.30891.18682.stgit@sofia.in.ibm.com> <20090615232318.74b099a6.akpm@linux-foundation.org> <20090616080715.GB7961@dirshya.in.ibm.com> Content-Type: text/plain Date: Wed, 17 Jun 2009 09:32:57 +0200 Message-Id: <1245223977.13761.21576.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1610 Lines: 41 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. -- 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/