Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759591AbZIPQZK (ORCPT ); Wed, 16 Sep 2009 12:25:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753093AbZIPQZH (ORCPT ); Wed, 16 Sep 2009 12:25:07 -0400 Received: from e28smtp09.in.ibm.com ([59.145.155.9]:39412 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752473AbZIPQZG (ORCPT ); Wed, 16 Sep 2009 12:25:06 -0400 Date: Wed, 16 Sep 2009 21:54:59 +0530 From: Dipankar Sarma To: Peter Zijlstra Cc: Gautham R Shenoy , Joel Schopp , Benjamin Herrenschmidt , Balbir Singh , Venkatesh Pallipadi , Vaidyanathan Srinivasan , Arun R Bharadwaj , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, "Darrick J. Wong" Subject: Re: [PATCH v3 0/3] cpu: pseries: Cpu offline states framework Message-ID: <20090916162459.GB12571@in.ibm.com> Reply-To: dipankar@in.ibm.com References: <20090915120629.20523.79019.stgit@sofia.in.ibm.com> <1253016701.5506.73.camel@laptop> <20090916152820.GA12571@in.ibm.com> <1253115171.7180.1.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1253115171.7180.1.camel@laptop> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2217 Lines: 46 On Wed, Sep 16, 2009 at 05:32:51PM +0200, Peter Zijlstra wrote: > On Wed, 2009-09-16 at 20:58 +0530, Dipankar Sarma wrote: > > On Tue, Sep 15, 2009 at 02:11:41PM +0200, Peter Zijlstra wrote: > > > On Tue, 2009-09-15 at 17:36 +0530, Gautham R Shenoy wrote: > > > > This patchset contains the offline state driver implemented for > > > > pSeries. For pSeries, we define three available_hotplug_states. They are: > > > > > > > > online: The processor is online. > > > > > > > > offline: This is the the default behaviour when the cpu is offlined > > > > > > > > inactive: This cedes the vCPU to the hypervisor with a cede latency > > > > > > > > Any feedback on the patchset will be immensely valuable. > > > > > > I still think its a layering violation... its the hypervisor manager > > > that should be bothered in what state an off-lined cpu is in. > > > > The problem is that all hypervisor managers cannot figure out what sort > > of latency guest OS can tolerate under the situation. They wouldn't know > > from what context guest OS has ceded the vcpu. It has to have > > some sort of hint, which is what the guest OS provides. > > I'm missing something here, hot-unplug is a slow path and should not > ever be latency critical..? You aren't, I did :) No, for this specific case, latency isn't an issue. The issue is - how do we cede unused vcpus to hypervisor for better energy management ? Yes, it can be done by a hypervisor manager telling the kernel to offline and make a bunch of vcpus "inactive". It does have to choose offline (release vcpu) vs. inactive (cede but guranteed if needed). The problem is that long ago we exported a lot of hotplug stuff to userspace through the sysfs interface and we cannot do something inside the kernel without keeping the sysfs stuff consistent. This seems like a sane way to do that without undoing all the virtual cpu hotplug infrastructure in different supporting archs. Thanks Dipankar -- 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/