----- Original Message ----- > From: "Itamar Heim" <[email protected]> > To: [email protected] > Cc: "engine-devel" <[email protected]> > Sent: Wednesday, December 5, 2012 3:56:02 PM > Subject: Re: [Engine-devel] host cpu feature > > On 12/05/2012 09:15 PM, [email protected] wrote: > > > > Quoting Doron Fediuck <[email protected]>: > > > >> ----- Original Message ----- > >>> From: "Laszlo Hornyak" <[email protected]> > >>> To: "Doron Fediuck" <[email protected]> > >>> Cc: "engine-devel" <[email protected]> > >>> Sent: Wednesday, December 5, 2012 7:14:46 PM > >>> Subject: Re: [Engine-devel] host cpu feature > >>> > >>> > >>> > >>> ----- Original Message ----- > >>> > From: "Doron Fediuck" <[email protected]> > >>> > To: "Yaniv Kaul" <[email protected]> > >>> > Cc: "Laszlo Hornyak" <[email protected]>, "engine-devel" > >>> > <[email protected]> > >>> > Sent: Wednesday, December 5, 2012 6:10:55 PM > >>> > Subject: Re: [Engine-devel] host cpu feature > >>> > > >>> > > Alternative idea, inspired by "Thus, if you hit any bugs, you > >>> > > are > >>> > > on > >>> > > your own" (http://libvirt.org/formatdomain.html#elementsCPU > >>> > > wrt > >>> > > 'host-passthrough'): > >>> > > A config option to determine if we use host-model or > >>> > > host-passthrough. > >>> > > Y. > >>> > > > >>> > > >>> > I do not think the engine should go to this level. > >>> > ie- it can ask for passthrough as a feature, and the > >>> > actual implementation is handled by vdsm. > >>> > > >>> > >>> If vdsm decides over host-passthrough or host-model, then how > >>> will > >>> the engine user know what exactly his VM gets. I think vdsm must > >>> be > >>> told exactly what to do. > >>> > >> > >> VDSM maintains some level of independence. This is why it the > >> engine > >> should be able to ask for passthrough as a feature. Otherwize vdsm > >> will > >> handle it. So for now I suggest we stick to passthrough only, and > >> if > >> we get an RFE for advanced mode we'll support the host model. > > > > What are we gaining by using passthrough over host-model? Looking > > at > > libvirt documentation, it seems that both modes give host CPU > > capabilities to guest VM. Whereas the downside of passthrough is > > that it > > limits migration. Whereas host-model will migrate to other hardware > > and > > if the destination hardware is better than source then the guest VM > > performance can be improved by rebooting guest. > > > > As a stretch goal, ovirt can keep track of host capabilities and > > inform > > the user after migrating to a better host, that a reboot may > > improve > > guest performance. > > pass-through may give better performance.
We need to be using -cpu host aka pass-through for performance. Selecting -cpu host on a Westmere cpu is different to -cpu Westmere on a Westmere cpu in terms of what the guest sees > host-model would be relevant when we can support live migration > inside > the cluster for some of the nodes, which will be relevant when the > scheduler is more pluggable/extendable than today. > _______________________________________________ > Engine-devel mailing list > [email protected] > http://lists.ovirt.org/mailman/listinfo/engine-devel > _______________________________________________ Engine-devel mailing list [email protected] http://lists.ovirt.org/mailman/listinfo/engine-devel
