From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756003Ab0CVTUt (ORCPT ); Mon, 22 Mar 2010 15:20:49 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:46526 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755521Ab0CVTUr (ORCPT ); Mon, 22 Mar 2010 15:20:47 -0400 Date: Mon, 22 Mar 2010 20:20:33 +0100 From: Ingo Molnar To: Avi Kivity Cc: Anthony Liguori , 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 , Gregory Haskins Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single project Message-ID: <20100322192033.GC21919@elte.hu> References: <20100322124428.GA12475@elte.hu> <4BA76810.4040609@redhat.com> <20100322143212.GE14201@elte.hu> <4BA7821C.7090900@codemonkey.ws> <20100322155505.GA18796@elte.hu> <4BA796DF.7090005@redhat.com> <20100322165107.GD18796@elte.hu> <4BA7A406.9050203@redhat.com> <20100322173400.GB15795@elte.hu> <4BA7AF2D.7060306@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BA7AF2D.7060306@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > > Lets look at the ${HOME}/.qemu/qmp/ enumeration method suggested by > > Anthony. There's numerous ways that this can break: > > I don't like it either. We have libvirt for enumerating guests. Which has pretty much the same problems to the ${HOME}/.qemu/qmp/ solution, obviously. > > - Those special files can get corrupted, mis-setup, get out of sync, or can > > be hard to discover. > > > > - The ${HOME}/.qemu/qmp/ solution suggested by Anthony has a very obvious > > design flaw: it is per user. When i'm root i'd like to query _all_ current > > guest images, not just the ones started by root. A system might not even > > have a notion of '${HOME}'. > > > > - Apps might start KVM vcpu instances without adhering to the > > ${HOME}/.qemu/qmp/ access method. > > - it doesn't work with nfs. So out of a list of 4 disadvantages your reply is that you agree with 3? > > - There is no guarantee for the Qemu process to reply to a request - while > > the kernel can always guarantee an enumeration result. I dont want 'perf > > kvm' to hang or misbehave just because Qemu has hung. > > If qemu doesn't reply, your guest is dead anyway. Erm, but i'm talking about a dead tool here. There's a world of a difference between 'kvm top' not showing new entries (because the guest is dead), and 'perf kvm top' hanging due to Qemu hanging. So it's essentially 4 our of 4. Yet your reply isnt "Ingo you are right" but "hey, too bad" ? > > Really, for such reasons user-space is pretty poor at doing system-wide > > enumeration and resource management. Microkernels lost for a reason. > > Take a look at your desktop, userspace is doing all of that everywhere, from > enumerating users and groups, to deciding how your disks are named. The > kernel only provides the bare facilities. We dont do that for robust system instrumentation, for heaven's sake! By your argument it would be perfectly fine to implement /proc purely via user-space, correct? > > You are committing several grave design mistakes here. > > I am committing on the shoulders of giants. Really, this is getting outright ridiculous. You agree with me that Anothony suggested a technically inferior solution, yet you even seem to be proud of it and are joking about it? And _you_ are complaining about lkml-style hard-talk discussions? Thanks, Ingo