Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754933AbZFGJOw (ORCPT ); Sun, 7 Jun 2009 05:14:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753198AbZFGJOm (ORCPT ); Sun, 7 Jun 2009 05:14:42 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:37328 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752803AbZFGJOl (ORCPT ); Sun, 7 Jun 2009 05:14:41 -0400 Date: Sun, 7 Jun 2009 11:13:49 +0200 From: Ingo Molnar To: Avi Kivity Cc: Linus Torvalds , George Dunlap , Thomas Gleixner , David Miller , "jeremy@goop.org" , Dan Magenheimer , "xen-devel@lists.xensource.com" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , Keir Fraser , "gregkh@suse.de" , "kurt.hackel@oracle.com" , Ian Pratt , "xen-users@lists.xensource.com" , ksrinivasan , "EAnderson@novell.com" , "wimcoekaerts@wimmekes.net" , Stephen Spector , "jens.axboe@oracle.com" , "npiggin@suse.de" Subject: Re: Xen is a feature Message-ID: <20090607091349.GA26897@elte.hu> References: <162f4c90-6431-4a2a-b337-6d7451d7b11e@default> <20090528001350.GD26820@elte.hu> <4A1F302E.8030501@goop.org> <20090528.210559.137121893.davem@davemloft.net> <4A1FCE8E.2060604@eu.citrix.com> <4A25564A.70608@eu.citrix.com> <4A257687.2030801@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A257687.2030801@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 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 Content-Length: 2682 Lines: 57 * Avi Kivity wrote: > Linus Torvalds wrote: >> The point? Xen really is horribly badly separated out. It gets way more >> incestuous with other systems than it should. It's entirely possible >> that this is very fundamental to both paravirtualization and to >> hypervisor behavior, but it doesn't matter - it just measn that I can >> well see that Xen is a f*cking pain to merge. >> >> So please, Xen people, look at your track record, and look at the >> issues from the standpoint of somebody merging your code, rather >> than just from the standpoint of somebody who whines "I want my >> code to be merged". >> >> IOW, if you have trouble getting your code merged, ask yourself >> what _you_ are doing wrong. > > There is in fact a way to get dom0 support with nearly no changes > to Linux, but it involves massive changes to Xen itself and > requires hardware support: run dom0 as a fully virtualized guest, > and assign it all the resources dom0 can access. It's probably a > massive effort though. > > I've considered it for kvm when faced with the "I want a thin > hypervisor" question: compile the hypervisor kernel with PCI > support but nothing else (no CONFIG_BLOCK or CONFIG_NET, no device > drivers), load userspace from initramfs, and assign host devices > to one or more privileged guests. You could probably run the host > with a heavily stripped configuration, and enjoy the slimness > while every interrupt invokes the scheduler, a context switch, and > maybe an IPI for good measure. This would be an acceptable model i suspect, if someone wants a 'slim hypervisor'. We can context switch way faster than we handle IRQs. Plus in a slimmed-down config we could intentionally slim down aspects of the scheduler as well, if it ever became a measurable performance issue. The hypervisor would run a minimal user-space and most of the context-switching overhead relates to having a full-fledged user-space with rich requirements. So there's no real conceptual friction between a 'lean and mean' hypervisor and a full-featured native kernel. This would certainly be an utterly clean design, and it would be interesting to see a Linux/Xen + Linux/Dom0 combo engineered in such a way - if people really find this layered kernel approach interesting. So the door is not closed to dom0 at all - but it has to be designed cleanly without messing up the native kernel. Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/