On Thu, Oct 05, 2017 at 02:11 PM +0200, Jiri Denemark <jdenemar@xxxxxxxxxx> wrote: > On Thu, Oct 05, 2017 at 10:46:24 +0200, Marc Hartmayer wrote: >> Let's assume we've a z13 system with a QEMU 2.9 and we define a domain >> using the default s390-virtio-ccw machine together with the host-model >> CPU mode. The definition will have the machine expanded to >> s390-virtio-ccw-2.9 but retain the host-model CPU mode. In a next step >> we upgrade to QEMU 2.10 (first version to recognize z14). Everything is >> still fine, even though the machine runs in 2.9 compatibility >> mode. Finally we upgrade to a z14. As a consequence it is not possible >> to start the domain anymore as the machine type doesn't support our CPU >> host model (which is expanded at start time of the domain). > > If I understand it correctly, when QEMU 2.10 is installed, we expand > the host-model CPU into a different model than with QEMU 2.9. And the > CPU model we got with QEMU 2.10 does not work with s390-virtio-ccw-2.9 > machine type even on QEMU 2.10. Is that correct? Right. > >> Is this behavior expected? > > Partially. > >> There are some ways to avoid this problem: >> - CPU model expansion is performed at domain definition time > > No, host-model is designed to be expanded when a domain starts so that > the same definition always results in the best CPU model to be used no > matter on which host the domain gest started. > >> - host-model is related to the machine type of a domain > > So if usability of a specific CPU model depends on the selected machine > types, we probably need to count with this restriction. Yep. > But it's going to be a bit complicated because we ask QEMU what the > host CPU is and the interface we used would need to be enhanced to > give us different results for all supported machine types so that we > can select the right one when a domain is started. So how do we deal with this? > > Jirka > -- Beste Grüße / Kind regards Marc Hartmayer IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen Registergericht: Amtsgericht Stuttgart, HRB 243294 -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
