Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751742Ab3CFQct (ORCPT ); Wed, 6 Mar 2013 11:32:49 -0500 Received: from e38.co.us.ibm.com ([32.97.110.159]:55009 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750742Ab3CFQcr (ORCPT ); Wed, 6 Mar 2013 11:32:47 -0500 Message-ID: <1362587352.6373.6.camel@lambeau> Subject: Re: [PATCH 0/4] Alter steal-time reporting in the guest From: Michael Wolf Reply-To: mjw@linux.vnet.ibm.com To: Glauber Costa Cc: Marcelo Tosatti , Frederic Weisbecker , linux-kernel@vger.kernel.org, riel@redhat.com, gleb@redhat.com, kvm@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, anthony@codemonkey.ws Date: Wed, 06 Mar 2013 10:29:12 -0600 In-Reply-To: <5136FAB4.4020305@parallels.com> References: <20130205214818.4615.12937.stgit@lambeau> <20130219011104.GA5785@amt.cnet> <1362514928.6267.16.camel@lambeau> <20130306014151.GB11481@amt.cnet> <5136FAB4.4020305@parallels.com> Organization: IBM-LTC Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13030616-5518-0000-0000-00000C4330C7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3074 Lines: 64 On Wed, 2013-03-06 at 12:13 +0400, Glauber Costa wrote: > On 03/06/2013 05:41 AM, Marcelo Tosatti wrote: > > On Tue, Mar 05, 2013 at 02:22:08PM -0600, Michael Wolf wrote: > >> Sorry for the delay in the response. I did not see the email > >> right away. > >> > >> On Mon, 2013-02-18 at 22:11 -0300, Marcelo Tosatti wrote: > >>> On Mon, Feb 18, 2013 at 05:43:47PM +0100, Frederic Weisbecker wrote: > >>>> 2013/2/5 Michael Wolf : > >>>>> In the case of where you have a system that is running in a > >>>>> capped or overcommitted environment the user may see steal time > >>>>> being reported in accounting tools such as top or vmstat. This can > >>>>> cause confusion for the end user. > >>>> > >>>> Sorry, I'm no expert in this area. But I don't really understand what > >>>> is confusing for the end user here. > >>> > >>> I suppose that what is wanted is to subtract stolen time due to 'known > >>> reasons' from steal time reporting. 'Known reasons' being, for example, > >>> hard caps. So a vcpu executing instructions with no halt, but limited to > >>> 80% of available bandwidth, would not have 20% of stolen time reported. > >> > >> Yes exactly and the end user many times did not set up the guest and is > >> not aware of the capping. The end user is only aware of the performance > >> level that they were told they would get with the guest. > >>> But yes, a description of the scenario that is being dealt with, with > >>> details, is important. > >> > >> I will add more detail to the description next time I submit the > >> patches. How about something like,"In a cloud environment the user of a > >> kvm guest is not aware of the underlying hardware or how many other > >> guests are running on it. The end user is only aware of a level of > >> performance that they should see." or does that just muddy the picture > >> more?? > > > > So the feature aims for is to report stolen time relative to hard > > capping. That is: stolen time should be counted as time stolen from > > the guest _beyond_ hard capping. Yes? > > > > Probably don't need to report new data to the guest for that. > > > If we take into account that 1 second always have one second, I believe > that you can just subtract the consigned time from the steal time the > host passes to the guest. > > During each second, the numbers won't sum up to 100. The delta to 100 is > the consigned time, if anyone cares. > > Adopting this would simplify this a lot. All you need to do, really, is > to get your calculation right from the bandwidth given by the cpu > controller. Subtract it in the host, and voila. I looked at doing that once but was told that I was changing the interface in an unacceptable way, because now I was not reporting all of the elapsed time. I agree it would make things simpler. > > -- 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/