Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753248AbZFELce (ORCPT ); Fri, 5 Jun 2009 07:32:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751211AbZFELc0 (ORCPT ); Fri, 5 Jun 2009 07:32:26 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:54829 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751088AbZFELcZ (ORCPT ); Fri, 5 Jun 2009 07:32:25 -0400 Date: Fri, 5 Jun 2009 17:02:17 +0530 From: Srivatsa Vaddagiri To: Paul Menage Cc: bharata@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Dhaval Giani , Balbir Singh , Vaidyanathan Srinivasan , Gautham R Shenoy , Ingo Molnar , Peter Zijlstra , Pavel Emelyanov , Avi Kivity , kvm@vger.kernel.org, Linux Containers , Herbert Poetzl Subject: Re: [RFC] CPU hard limits Message-ID: <20090605113217.GA20786@in.ibm.com> Reply-To: vatsa@in.ibm.com References: <20090604053649.GA3701@in.ibm.com> <6599ad830906050153i1afd104fqe70f681317349142@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6599ad830906050153i1afd104fqe70f681317349142@mail.gmail.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: 955 Lines: 20 On Fri, Jun 05, 2009 at 01:53:15AM -0700, Paul Menage wrote: > 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? I think the interval over which we need guarantee matters here. Shares can generally provide guaranteed share of resource over longer (sometimes minutes) intervals. For high-priority bursty workloads, the latency in achieving guaranteed resource usage matters. By having hard-limits, we are "reserving" (potentially idle) slots where the high-priority group can run and claim its guaranteed share almost immediately. - vatsa -- 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/