Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756311AbZFENno (ORCPT ); Fri, 5 Jun 2009 09:43:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755277AbZFENnh (ORCPT ); Fri, 5 Jun 2009 09:43:37 -0400 Received: from e28smtp09.in.ibm.com ([59.145.155.9]:46437 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755155AbZFENng (ORCPT ); Fri, 5 Jun 2009 09:43:36 -0400 Date: Fri, 5 Jun 2009 19:13:20 +0530 From: Dhaval Giani To: Avi Kivity Cc: Paul Menage , bharata@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Balbir Singh , Vaidyanathan Srinivasan , Gautham R Shenoy , Srivatsa Vaddagiri , Ingo Molnar , Peter Zijlstra , Pavel Emelyanov , kvm@vger.kernel.org, Linux Containers , Herbert Poetzl Subject: Re: [RFC] CPU hard limits Message-ID: <20090605134320.GA3994@linux.vnet.ibm.com> Reply-To: Dhaval Giani References: <20090604053649.GA3701@in.ibm.com> <6599ad830906050153i1afd104fqe70f681317349142@mail.gmail.com> <4A291753.7090205@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A291753.7090205@redhat.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: 1809 Lines: 50 On Fri, Jun 05, 2009 at 04:02:11PM +0300, Avi Kivity wrote: > Paul Menage wrote: >> On Wed, Jun 3, 2009 at 10:36 PM, Bharata B >> Rao wrote: >> >>> - Hard limits can be used to provide guarantees. >>> >>> >> >> This claim (and the subsequent long thread it generated on how limits >> can provide guarantees) confused me a bit. >> >> Why do we need limits to provide guarantees when we can already >> provide guarantees via shares? >> >> Suppose 10 cgroups each want 10% of the machine's CPU. We can just >> give each cgroup an equal share, and they're guaranteed 10% if they >> try to use it; if they don't use it, other cgroups can get access to >> the idle cycles. >> >> Suppose cgroup A wants a guarantee of 50% and two others, B and C, >> want guarantees of 15% each; give A 50 shares and B and C 15 shares >> each. In this case, if they all run flat out they'll get 62%/19%/19%, >> which is within their SLA. >> >> That's not to say that hard limits can't be useful in their own right >> - e.g. for providing reproducible loadtesting conditions by >> controlling how much CPU a service can use during the load test. But I >> don't see why using them to implement guarantees is either necessary >> or desirable. >> >> (Unless I'm missing some crucial point ...) >> > > How many shares does a cgroup with a 0% guarantee get? > Shares cannot be used to provide guarantees. All they decide is what propotion groups can get CPU time. (yes, shares is a bad name, weight shows the intent better). thanks, -- regards, Dhaval -- 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/