From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43808) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7Rps-00025Z-Ch for qemu-devel@nongnu.org; Tue, 23 Jun 2015 13:18:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z7Rpo-0007Px-3w for qemu-devel@nongnu.org; Tue, 23 Jun 2015 13:18:12 -0400 Received: from cantor2.suse.de ([195.135.220.15]:38762 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7Rpn-0007Pt-RH for qemu-devel@nongnu.org; Tue, 23 Jun 2015 13:18:08 -0400 Message-ID: <558994CE.9050001@suse.de> Date: Tue, 23 Jun 2015 19:18:06 +0200 From: =?windows-1252?Q?Andreas_F=E4rber?= MIME-Version: 1.0 References: <20150608201835.GM3525@orkuz.home> <558951C0.3050806@suse.de> <20150623150828.GD3134@thinpad.lan.raisama.net> <20150623173048-mutt-send-email-mst@redhat.com> <20150623155832.GE3134@thinpad.lan.raisama.net> <55898637.6080804@suse.de> <20150623162555.GL30318@redhat.com> <20150623183115-mutt-send-email-mst@redhat.com> <20150623163858.GG3134@thinpad.lan.raisama.net> <55898D09.2060405@suse.de> <20150623170859.GH3134@thinpad.lan.raisama.net> In-Reply-To: <20150623170859.GH3134@thinpad.lan.raisama.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: mimu@linux.vnet.ibm.com, "Michael S. Tsirkin" , qemu-devel@nongnu.org, Alexander Graf , borntraeger@de.ibm.com, Igor Mammedov , Paolo Bonzini , Jiri Denemark , rth@twiddle.net Am 23.06.2015 um 19:08 schrieb Eduardo Habkost: > On Tue, Jun 23, 2015 at 06:44:57PM +0200, Andreas F=E4rber wrote: >> Am 23.06.2015 um 18:38 schrieb Eduardo Habkost: >>> On Tue, Jun 23, 2015 at 06:33:05PM +0200, Michael S. Tsirkin wrote: >>>> On Tue, Jun 23, 2015 at 05:25:55PM +0100, Daniel P. Berrange wrote: >>>>> Whether QEMU changed the CPU for existing machines, or only for new >>>>> machines is actually not the core problem. Even if we only changed >>>>> the CPU in new machines that would still be an unsatisfactory situa= tion >>>>> because we want to be able to be able to access different versions = of >>>>> the CPU without the machine type changing, and access different ver= sions >>>>> of the machine type, without the CPU changing. IOW it is the fact t= hat the >>>>> changes in CPU are tied to changes in machine type that is the core >>>>> problem. >>>> >>>> But that's because we are fixing bugs. If CPU X used to work on >>>> hardware Y in machine type A and stopped in machine type B, this is >>>> because we have determined that it's the right thing to do for the >>>> guests and the users. We don't break stuff just for fun. >>>> Why do you want to bring back the bugs we fixed? >>> >>> I didn't take the time to count them, but I bet most of the commits I >>> listed on my previous e-mail message are not bug fixes, but new >>> features. >> >> Huh? Of course the latest machine model get new features. The point is >> that the previous ones don't and that's what we are providing them for= - >> libvirt is expected to choose one machine and the contract with QEMU i= s >> that for that machine the CPU does *not* grow new features, and we're >> going at great lengths to achieve that. So this thread feels more and >> more weird... >=20 > We are not talking about changes to existing machines. We are talking > about having changes introduced in new machines (the one we did on > purpose) affecting the runnability of the VM. You are talking abstract! Example 1: Point A: Machine pc-i440fx-2.3 exists Runs or runs not. Point B: Machine pc-i440fx-2.3 still exists Still runs or runs not due to guest ABI stability rules. Example 2: Point A: pc-i440fx-2.4 does not exist in 2.3 Does not run becomes it doesn't exist. Point B: New pc-i440fx-2.4 Runs or does not run, and if so has more features than pc-i440fx-2.3. There is no runnability problem - either it runs or it doesn't, but there's no change over time. This is what the machine -x.y versioning is all about. Andreas --=20 SUSE Linux GmbH, Maxfeldstr. 5, 90409 N=FCrnberg, Germany GF: Felix Imend=F6rffer, Jane Smithard, Dilip Upmanyu, Graham Norton; HRB 21284 (AG N=FCrnberg)