From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752787Ab0CUTR6 (ORCPT ); Sun, 21 Mar 2010 15:17:58 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:54700 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751337Ab0CUTR4 (ORCPT ); Sun, 21 Mar 2010 15:17:56 -0400 Date: Sun, 21 Mar 2010 20:17:42 +0100 From: Ingo Molnar To: Anthony Liguori Cc: Avi Kivity , Pekka Enberg , "Zhang, Yanmin" , Peter Zijlstra , Sheng Yang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marcelo Tosatti , oerg Roedel , Jes Sorensen , Gleb Natapov , Zachary Amsden , ziteng.huang@intel.com, Arnaldo Carvalho de Melo , Fr?d?ric Weisbecker Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single project Message-ID: <20100321191742.GD25922@elte.hu> References: <4BA250BF.80704@codemonkey.ws> <20100318162853.GB447@elte.hu> <4BA256FE.5080501@codemonkey.ws> <84144f021003180951s5207de16p1cdf4b9b04040222@mail.gmail.com> <20100318170223.GB9756@elte.hu> <4BA25E66.2050800@redhat.com> <20100318172805.GB26067@elte.hu> <4BA32E1A.2060703@redhat.com> <20100319085346.GG12576@elte.hu> <4BA3747F.60401@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BA3747F.60401@codemonkey.ws> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: 0.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.0 required=5.9 tests=none autolearn=no SpamAssassin version=3.2.5 _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Anthony Liguori wrote: > On 03/19/2010 03:53 AM, Ingo Molnar wrote: > >* Avi Kivity wrote: > > > >>>There were two negative reactions immediately, both showed a fundamental > >>>server versus desktop bias: > >>> > >>> - you did not accept that the most important usecase is when there is a > >>> single guest running. > >>Well, it isn't. > >Erm, my usability points are _doubly_ true when there are multiple guests ... > > > >The inconvenience of having to type: > > > > perf kvm --host --guest --guestkallsyms=/home/ymzhang/guest/kallsyms \ > > --guestmodules=/home/ymzhang/guest/modules top > > > >is very obvious even with a single guest. Now multiply that by more guests ... > > If you want to improve this, you need to do the following: > > 1) Add a userspace daemon that uses vmchannel that runs in the guest and can > fetch kallsyms and arbitrary modules. If that daemon lives in > tools/perf, that's fine. Adding any new daemon to an existing guest is a deployment and usability nightmare. The basic rule of good instrumentation is to be transparent. The moment we have to modify the user-space of a guest just to monitor it, the purpose of transparent instrumentation is defeated. That was one of the fundamental usability mistakes of Oprofile. There is no 'perf' daemon - all the perf functionality is _built in_, and for very good reasons. It is one of the main reasons for perf's success as well. Now Qemu is trying to repeat that stupid mistake ... So please either suggest a different transparent solution that is technically better than the one i suggested, or you should concede the point really. Please try think with the heads of our users and developers and dont suggest some weird ivory-tower design that is totally impractical ... And no, you have to code none of this, we'll do all the coding. The only thing we are asking is for you to not stand in the way of good usability ... Thanks, Ingo