From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37669) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7QTg-0005mY-14 for qemu-devel@nongnu.org; Tue, 23 Jun 2015 11:51:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z7QTa-00078f-45 for qemu-devel@nongnu.org; Tue, 23 Jun 2015 11:51:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45733) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z7QTZ-00078P-TL for qemu-devel@nongnu.org; Tue, 23 Jun 2015 11:51:06 -0400 Date: Tue, 23 Jun 2015 16:51:00 +0100 From: "Daniel P. Berrange" Message-ID: <20150623155100.GJ30318@redhat.com> References: <1433790460-30679-1-git-send-email-ehabkost@redhat.com> <20150608201835.GM3525@orkuz.home> <558951C0.3050806@suse.de> <20150623150828.GD3134@thinpad.lan.raisama.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150623150828.GD3134@thinpad.lan.raisama.net> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 0/2] target-i386: "custom" CPU model + script to dump existing CPU models Reply-To: "Daniel P. Berrange" 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 , Andreas =?utf-8?Q?F=C3=A4rber?= , rth@twiddle.net On Tue, Jun 23, 2015 at 12:08:28PM -0300, Eduardo Habkost wrote: > On Tue, Jun 23, 2015 at 02:32:00PM +0200, Andreas F=C3=A4rber wrote: > > Am 08.06.2015 um 22:18 schrieb Jiri Denemark: > > >> To help libvirt in the transition, a x86-cpu-model-dump script is = provided, > > >> that will generate a config file that can be loaded using -readcon= fig, based on > > >> the -cpu and -machine options provided in the command-line. > > >=20 > > > Thanks Eduardo, I never was a big fan of moving (or copying) all th= e CPU > > > configuration data to libvirt, but now I think it actually makes se= nse. > > > We already have a partial copy of CPU model definitions in libvirt > > > anyway, but as QEMU changes some CPU models in some machine types (= and > > > libvirt does not do that) we have no real control over the guest CP= U > > > configuration. While what we really want is full control to enforce > > > stable guest ABI. > >=20 > > That sounds like FUD to me. Any concrete data points where QEMU does = not > > have a stable ABI for x86 CPUs? That's what we have the pc*-x.y machi= nes > > for. >=20 > What Jiri is saying that the CPUs change depending on -mmachine, not > that the ABI is broken by a given machine. >=20 > The problem here is that libvirt needs to provide CPU models whose > runnability does not depend on the machine-type. If users have a VM tha= t > is running in a host and the VM machine-type changes, the VM should be > still runnable in that host. QEMU doesn't provide that, our CPU models > may change when we introduce new machine-types, so we are giving them a > mechanism that allows libvirt to implement the policy they need. Expanding on that, but tieing the CPU model to the machine type, QEMU has in turn effectively tied the machine type to the host hardware. eg, switching to a newer machine type, may then prevent the guest from being able to launch on the hardware that it was previously able to run on, due to some new requirement of the CPU model associated with the machine type. Libvirt wants the CPU models to be independant of the machine type, so in general only the CPU model is dependant on hardware capabilities and machine type is isolated from hardware. Libvirt still intends to do versioning of the CPU models, but the versioning will be separate from the versioning of the machine types, and will be handled by libvirt itself. This also allows us to get further towards our goal which is to have a consistent representation of CPU models across all libvirt hypervisors. eg the same libvirt CPU model and versions can be made consistent across kvm, xen, vmware, etc, as they're not longer changing behind our back based on the qemu machine type. Regards, Daniel --=20 |: http://berrange.com -o- http://www.flickr.com/photos/dberrange= / :| |: http://libvirt.org -o- http://virt-manager.or= g :| |: http://autobuild.org -o- http://search.cpan.org/~danberr= / :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vn= c :|