On Wed, Jun 01, 2016 at 14:23:54 +0300, Nikolay Shirokovskiy wrote: > Hi, everyone. > > Cpu mode 'host-model' is not convinient for migration in current form. > Consider migration from less capable host to more capable one - it is > possible. > But then migration backwards is impossible despite the fact that qemu process > on destination is running with the same model and features as on source > because > migration does not update 'host-model' cpu upon migration on destination. The > problem is that on migrating back instead of taking current cpu config > 'host-model' is expanded again and gain extra features of destination and > migration failed by source (new destination) side. > > What if we change cpu for active config from 'host-model' into 'custom' in > the starting process? Then this issue will be fixed. It is quite reasonable > from my POV - 'host-model' is effectively about taking active domain cpu from > host on > start, after that active domain cpu is on its own. Persistent config stays > 'host-model' so migrating of active domain and restarting it gains extra > features of new host as before.
Yeah, your thoughts go in the right direction, although it's not enough. We also need to start creating better CPU specifications for host-model and we need to start checking QEMU gives us what we asked for. For all these reasons host-model is currently completely broken, although it usually just works (until you start looking closer at it) :-) Anyway, I'm working on all these (and other) issues with our CPU configuration code and you can expect patches coming to libvirt-list this month. Jirka -- libvir-list mailing list [email protected] https://www.redhat.com/mailman/listinfo/libvir-list
