Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161471AbWHDV0S (ORCPT ); Fri, 4 Aug 2006 17:26:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161479AbWHDV0S (ORCPT ); Fri, 4 Aug 2006 17:26:18 -0400 Received: from gw.goop.org ([64.81.55.164]:35009 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1161471AbWHDV0R (ORCPT ); Fri, 4 Aug 2006 17:26:17 -0400 Message-ID: <44D3BB7C.4000001@goop.org> Date: Fri, 04 Aug 2006 14:26:20 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.4 (X11/20060613) MIME-Version: 1.0 To: David Lang CC: Arjan van de Ven , Antonio Vargas , Rusty Russell , Andrew Morton , jeremy@xensource.com, greg@kroah.com, zach@vmware.com, linux-kernel@vger.kernel.org, torvalds@osdl.org, hch@infradead.org, jlo@vmware.com, xen-devel@lists.xensource.com, simon@xensource.com, ian.pratt@xensource.com Subject: Re: A proposal - binary References: <44D1CC7D.4010600@vmware.com> <20060803190605.GB14237@kroah.com> <44D24DD8.1080006@vmware.com> <20060803200136.GB28537@kroah.com> <44D2B678.6060400@xensource.com> <20060803211850.3a01d0cc.akpm@osdl.org> <1154667875.11382.37.camel@localhost.localdomain> <20060803225357.e9ab5de1.akpm@osdl.org> <1154675100.11382.47.camel@localhost.localdomain> <69304d110608041146t44077033j9a10ae6aee19a16d@mail.gmail.com> <44D39F73.8000803@linux.intel.com> <44D3A9F3.2000000@goop.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 27 David Lang wrote: > how can I compile in support for Xen4 on my 2.6.18 kernel? after all > xen 2 and xen3 are incompatable hypervisors so why wouldn't xen4 (and > I realize there is no xen4 yet, but there is likly to be one during > the time virtual servers created with 2.6.18 are still running) Firstly, backwards compatibility is very important; I would guess that if there were a Xen4 ABI, the hypervisor would still support Xen3 for some time. Secondly, if someone goes to the effort of backporting a Xen4 paravirtops driver for 2.6.18, then you could compile it in. > I also am missing something here. how can a system be compiled to do > several different things for the same privilaged opcode (including > running that opcode) without turning that area of code into a > performance pig as it checks for each possible hypervisor being present? Conceptually, the paravirtops structure is a structure of pointers to functions which get filled in at runtime to support whatever hypervisor we're running over. But it also has the means to patch inline versions of the appropriate code sequences for performance-critical operations. J - 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/