From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by bilbo.ozlabs.org (Postfix) with ESMTP id 0F9C6B6EDE for ; Fri, 7 Aug 2009 11:03:01 +1000 (EST) Date: Fri, 7 Aug 2009 09:02:56 +0800 From: Shaohua Li To: Gautham R Shenoy Subject: Re: [PATCH 0/3] cpu: idle state framework for offline CPUs. Message-ID: <20090807010256.GA21904@sli10-desk.sh.intel.com> References: <20090805142311.553.78286.stgit@sofia.in.ibm.com> <20090806015855.GA20596@sli10-desk.sh.intel.com> <20090806134844.GA19146@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20090806134844.GA19146@in.ibm.com> Cc: "Brown, Len" , Peter Zijlstra , "linux-kernel@vger.kernel.org" , "Pallipadi, Venkatesh" , Ingo Molnar , "linuxppc-dev@lists.ozlabs.org" , "Darrick J. Wong" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, Aug 06, 2009 at 09:48:44PM +0800, Gautham R Shenoy wrote: > Hi Shaohua, > > On Thu, Aug 06, 2009 at 09:58:55AM +0800, Shaohua Li wrote: > > Hi, > > > > On Wed, Aug 05, 2009 at 10:25:53PM +0800, Gautham R Shenoy wrote: > > > In this patch-series, we propose to extend the CPU-Hotplug infrastructure > > > and allow the system administrator to choose the desired state the CPU should > > > go to when it is offlined. We think this approach addresses the concerns about > > > determinism as well as transparency, since CPU-Hotplug already provides > > > notification mechanism which the userspace can listen to for any change > > > in the configuration and correspondingly readjust any previously set > > > cpu-affinities. > > Peter dislikes any approach (including cpuhotplug) which breaks userspace policy, > > even userspace can get a notification. > > I think Peter's problem was more to do with the kernel offlining the CPUs > behind the scenes, right ? > > We don't do that in this patch series. The option to offline the CPUs is > very much with the admin. The patch-series only provides the interface > that helps the admin choose the state the CPU must reside in when it > goes offline. but the goal is to use cpu offline to save power, right? So we still have Peter's problem. > > > Also, approaches such as [1] can make use of this > > > extended infrastructure instead of putting the CPU to an arbitrary C-state > > > when it is offlined, thereby providing the system administrator a rope to hang > > > himself with should he feel the need to do so. > > I didn't see the reason why administrator needs to know which state offline cpu > > should stay. Don't know about powerpc side, but in x86 side, it appears deepest > > C-state is already preferred. > > We can still provide a sane default value based on what states are > available and what the BIOS limits us to. Thus we can still use the > idle-state-offline patch that Venki posted sometime ago, right ? My original concern about Venki's patch is the C-state limition, but Venki thought if CPU has the limition, CPU should disable specific C-state, so this isn't a problem. I had no objection about the infrastructure itself, but just wonder why we need it. Thanks, Shaohua