From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting Date: Sat, 11 Dec 2010 09:31:24 +0200 Message-ID: <4D0328CC.1020809@redhat.com> References: <20101202144129.4357fe00@annuminas.surriel.com> <20101210050344.GR3158@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Rik van Riel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Srivatsa Vaddagiri , Peter Zijlstra , Ingo Molnar , Anthony Liguori To: balbir@linux.vnet.ibm.com Return-path: In-Reply-To: <20101210050344.GR3158@balbir.in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 12/10/2010 07:03 AM, Balbir Singh wrote: > > > > Scheduler people, please flame me with anything I may have done > > wrong, so I can do it right for a next version :) > > > > This is a good problem statement, there are other things to consider > as well > > 1. If a hard limit feature is enabled underneath, donating the > timeslice would probably not make too much sense in that case What's the alternative? Consider a two vcpu guest with a 50% hard cap. Suppose the workload involves ping-ponging within the guest. If the scheduler decides to schedule the vcpus without any overlap, then the throughput will be dictated by the time slice. If we allow donation, throughput is limited by context switch latency. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.