Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752642AbZFEFLK (ORCPT ); Fri, 5 Jun 2009 01:11:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752945AbZFEFK4 (ORCPT ); Fri, 5 Jun 2009 01:10:56 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:59359 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750973AbZFEFKz (ORCPT ); Fri, 5 Jun 2009 01:10:55 -0400 Date: Fri, 5 Jun 2009 13:10:50 +0800 From: Balbir Singh To: Avi Kivity Cc: bharata@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Dhaval Giani , 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: <20090605051050.GB11755@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090604053649.GA3701@in.ibm.com> <4A27BBCA.5020606@redhat.com> <20090605030309.GA3872@in.ibm.com> <4A28921C.6010802@redhat.com> <661de9470906042137u603e2997n80c270bf7f6191ad@mail.gmail.com> <4A28A2AB.3060108@redhat.com> <20090605044946.GA11755@balbir.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20090605044946.GA11755@balbir.in.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: 2647 Lines: 67 * Balbir Singh [2009-06-05 12:49:46]: > * Avi Kivity [2009-06-05 07:44:27]: > > > Balbir Singh wrote: > >> On Fri, Jun 5, 2009 at 11:33 AM, Avi Kivity wrote: > >> > >>> Bharata B Rao wrote: > >>> > >>>>> Another way is to place the 8 groups in a container group, and limit > >>>>> that to 80%. But that doesn't work if I want to provide guarantees to > >>>>> several groups. > >>>>> > >>>>> > >>>> Hmm why not ? Reduce the guarantee of the container group and provide > >>>> the same to additional groups ? > >>>> > >>>> > >>> This method produces suboptimal results: > >>> > >>> $ cgroup-limits 10 10 0 > >>> [50.0, 50.0, 40.0] > >>> > >>> I want to provide two 10% guaranteed groups and one best-effort group. > >>> Using the limits method, no group can now use more than 50% of the > >>> resources. However, having the first group use 90% of the resources does > >>> not violate any guarantees, but it not allowed by the solution. > >>> > >>> > >> > >> How, it works out fine in my calculation > >> > >> 50 + 40 for G2 and G3, make sure that G1 gets 10%, since others are > >> limited to 90% > >> 50 + 40 for G1 and G3, make sure that G2 gets 10%, since others are > >> limited to 90% > >> 50 + 50 for G1 and G2, make sure that G3 gets 0%, since others are > >> limited to 100% > >> > > > > It's fine in that it satisfies the guarantees, but it is deeply > > suboptimal. If I ran a cpu hog in the first group, while the other two > > were idle, it would be limited to 50% cpu. On the other hand, if it > > consumed all 100% cpu it would still satisfy the guarantees (as the > > other groups are idle). > > > > The result is that in such a situation, wall clock time would double > > even though cpu resources are available. > > But then there is no other way to make a *guarantee*, guarantees come > at a cost of idling resources, no? Can you show me any other > combination that will provide the guarantee and without idling the > system for the specified guarantees? OK, I see part of your concern, but I think we could do some optimizations during design. For example if all groups have reached their hard-limit and the system is idle, should we do start a new hard limit interval and restart, so that idleness can be removed. Would that be an acceptable design point? -- Balbir -- 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/