From mboxrd@z Thu Jan 1 00:00:00 1970 From: Antoine Martin Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single project Date: Mon, 22 Mar 2010 02:35:13 +0700 Message-ID: <4BA674F1.6070603@nagafix.co.uk> 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> <20100321191742.GD25922@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , 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 To: Ingo Molnar Return-path: Received: from mamba.nagafix.co.uk ([194.145.196.68]:55537 "EHLO mail.nagafix.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751337Ab0CUTfZ (ORCPT ); Sun, 21 Mar 2010 15:35:25 -0400 In-Reply-To: <20100321191742.GD25922@elte.hu> Sender: kvm-owner@vger.kernel.org List-ID: On 03/22/2010 02:17 AM, Ingo Molnar wrote: > * 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. > Absolutely. In most cases it is not desirable, and you'll find that in a lot of cases it is not even possible - for non-technical reasons. One of the main benefits of virtualization is the ability to manage and see things from the outside. > 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. > Not to mention Heisenbugs and interference. Cheers Antoine > 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 > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >