Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755257AbZFGKhI (ORCPT ); Sun, 7 Jun 2009 06:37:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754629AbZFGKg6 (ORCPT ); Sun, 7 Jun 2009 06:36:58 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:54369 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754619AbZFGKg5 (ORCPT ); Sun, 7 Jun 2009 06:36:57 -0400 Date: Sun, 7 Jun 2009 12:35:47 +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: <20090607103547.GR31286@elte.hu> References: <4A1F302E.8030501@goop.org> <20090528.210559.137121893.davem@davemloft.net> <4A1FCE8E.2060604@eu.citrix.com> <4A25564A.70608@eu.citrix.com> <4A257687.2030801@redhat.com> <20090607091349.GA26897@elte.hu> <4A2B9001.7090706@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A2B9001.7090706@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: 1931 Lines: 44 * Avi Kivity wrote: > Ingo Molnar wrote: >>> 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. >> > > The context switch would be taken by the Xen scheduler, not the Linux > scheduler. [...] The 'slim hypervisor' model i was suggesting was a slimmed down _Linux_ 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/