Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754593AbZF0L11 (ORCPT ); Sat, 27 Jun 2009 07:27:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754718AbZF0L1K (ORCPT ); Sat, 27 Jun 2009 07:27:10 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:40775 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755038AbZF0L1F (ORCPT ); Sat, 27 Jun 2009 07:27:05 -0400 Date: Wed, 24 Jun 2009 17:02:40 +0200 From: Pavel Machek To: "Paul E. McKenney" Cc: Vaidyanathan Srinivasan , Andrew Morton , Gautham R Shenoy , linux-kernel@vger.kernel.org, Peter Zijlstra , Balbir Singh , Rusty Russel , Nathan Lynch , Ingo Molnar , Venkatesh Pallipadi , Dipankar Sarma , Shoahua Li Subject: Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support. Message-ID: <20090624150240.GB1784@ucw.cz> References: <20090616053431.30891.18682.stgit@sofia.in.ibm.com> <20090615232318.74b099a6.akpm@linux-foundation.org> <20090616080715.GB7961@dirshya.in.ibm.com> <20090616210059.GL6842@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090616210059.GL6842@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2144 Lines: 50 On Tue 2009-06-16 14:00:59, Paul E. McKenney wrote: > On Tue, Jun 16, 2009 at 01:37:15PM +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 > > Perhaps also reducing boot-up time? If I am correctly interpreting the > above numbers, an eight-CPU system would be consuming 175 milliseconds > bringing up the seven non-boot CPUs. Reducing this by 150 milliseconds > might be of interest to some people. ;-) ...also it should save 300msec from s2ram cycle. Actually maybe suspend code should be modified first, as it can demonstrate the changes without kernel<-> user interface changing? -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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/