From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751380AbbJHFFw (ORCPT ); Thu, 8 Oct 2015 01:05:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:35484 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751000AbbJHFFv (ORCPT ); Thu, 8 Oct 2015 01:05:51 -0400 Subject: Re: [RFC PATCH] Use vAPIC when doing IPI for PVHVM guests. To: Konrad Rzeszutek Wilk , boris.ostrovsky@oracle.com, joao.m.martins@oracle.com, david.vrabel@citrix.com, dario.faggioli@citrix.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <1444249310-23433-1-git-send-email-konrad.wilk@oracle.com> From: Juergen Gross Message-ID: <5615F9AD.101@suse.com> Date: Thu, 8 Oct 2015 07:05:49 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <1444249310-23433-1-git-send-email-konrad.wilk@oracle.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/07/2015 10:21 PM, Konrad Rzeszutek Wilk wrote: > Hey, > > I was running some tools in which we would heavily do rescheduling > of events - and realized to my surprise that the event channels (and > the hypercall) would slow things down. If I used the vAPIC with its > IPI support (so no VMEXIT) I got much much better performance. > > Now this is an RFC because: > 1). I hadn't verified from the xentrace how much less VMEXITS we get. > But I remember Boris's patches and they gave at least 10%. > I think this will get the same performance or even better. > > 2). I don't know what to do with migration. That is if the guest > migrates to older hardware it needs to recheck this I presume? Same problem applies to many other features. In case you want to migrate to a machine with less features you'd have to mask those features in the cpuid data of the domain. > 3). Should this be enabled by default? I did get better performance > but that was synthetic. Having some benchmark results would help to decide this. :-) I'd be especially interested in checking "no vcpu over-commitment" and "heavy vcpu over-commitment" scenarios regarding the effect of the feature. > > Thoughts? I like the idea. Juergen