From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chris Friesen" Subject: Re: [RFC] CPU hard limits Date: Fri, 05 Jun 2009 08:44:15 -0600 Message-ID: <4A292F3F.8010402@nortel.com> References: <20090604053649.GA3701@in.ibm.com> <6599ad830906050153i1afd104fqe70f681317349142@mail.gmail.com> <20090605113217.GA20786@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Paul Menage , 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 To: vatsa@in.ibm.com Return-path: Received: from zcars04e.nortel.com ([47.129.242.56]:44863 "EHLO zcars04e.nortel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751263AbZFEOoW (ORCPT ); Fri, 5 Jun 2009 10:44:22 -0400 In-Reply-To: <20090605113217.GA20786@in.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Srivatsa Vaddagiri wrote: > 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. Why do you need to "reserve" it though? By definition, if it's high-priority then it should be able to interrupt the currently running task. Chris