From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756928Ab2ADU5M (ORCPT ); Wed, 4 Jan 2012 15:57:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:31237 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756201Ab2ADU5J (ORCPT ); Wed, 4 Jan 2012 15:57:09 -0500 Message-ID: <4F04BD11.8090302@redhat.com> Date: Wed, 04 Jan 2012 15:56:49 -0500 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: Avi Kivity CC: Nikunj A Dadhania , Ingo Molnar , peterz@infradead.org, linux-kernel@vger.kernel.org, vatsa@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS References: <20111219083141.32311.9429.stgit@abhimanyu.in.ibm.com> <20111219112326.GA15090@elte.hu> <87sjke1a53.fsf@abhimanyu.in.ibm.com> <4EF1B85F.7060105@redhat.com> <877h1o9dp7.fsf@linux.vnet.ibm.com> <20111223103620.GD4749@elte.hu> <4EF701C7.9080907@redhat.com> <20111230095147.GA10543@elte.hu> <878vlu4bgh.fsf@linux.vnet.ibm.com> <87pqf5mqg4.fsf@abhimanyu.in.ibm.com> <4F017AD2.3090504@redhat.com> <87mxa3zqm1.fsf@abhimanyu.in.ibm.com> <4F046536.5080207@redhat.com> <4F048295.1050907@redhat.com> <4F04898B.1080600@redhat.com> In-Reply-To: <4F04898B.1080600@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/04/2012 12:16 PM, Avi Kivity wrote: > On 01/04/2012 06:47 PM, Rik van Riel wrote: >>> So it looks like the default is optimal, at least wrt the cases you >>> tested and your test workload. >> >> >> It depends on the workload. >> >> I believe ebizzy synchronously bounces messages around between >> userland threads, and may benefit from lower latency preemption >> and re-scheduling. >> >> Workloads like AMQP do asynchronous messaging, and are likely >> to benefit from having a lower number of switches. >> >> I do not know which kind of workload is more prevalent. >> >> Another worry with gang scheduling is scalability. One of >> the reasons Linux scales well to larger systems is that a >> lot of things are done CPU local, without communicating >> things with other CPUs. Making the scheduling algorithm >> system-global has the potential to add in a lot of overhead. >> >> Likewise, removing the ability to migrate workloads to idle >> CPUs is likely to hurt a lot of real world workloads. >> >> Benchmarks don't care, because they run full-out. However, >> users do not run benchmarks nearly as much as they run >> actual workloads... >> > > I think we can solve it at the guest level. The paravirt ticketlock > stuff introduces wait/wake calls (actually wait is just a HLT > instruction); we could spin for a while, then HLT until the other side > wakes us. We should do this for all sites that busy wait. Agreed, that would probably be the best (and nicest) solution. -- All rights reversed