Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755601AbZFGMsh (ORCPT ); Sun, 7 Jun 2009 08:48:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755062AbZFGMsV (ORCPT ); Sun, 7 Jun 2009 08:48:21 -0400 Received: from mx2.redhat.com ([66.187.237.31]:46038 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755216AbZFGMsT (ORCPT ); Sun, 7 Jun 2009 08:48:19 -0400 Message-ID: <4A2BB6B1.4040805@redhat.com> Date: Sun, 07 Jun 2009 15:46:41 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Ingo Molnar 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 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> <20090607103547.GR31286@elte.hu> In-Reply-To: <20090607103547.GR31286@elte.hu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2184 Lines: 52 Ingo Molnar wrote: > * 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. > Yeah, I lost the context. I should reduce my own context switching. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- 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/