Re: [Engine-devel] host cpu feature

From: "Itamar Heim" <iheim(a)redhat.com&gt; To: snmishra(a)linux.vnet.ibm.com Cc: "engine-devel" <engine-devel(a)ovirt.org&gt; Sent: Wednesday, December 5, 2012 3:56:02 PM Subject: Re: [Engine-devel] host cpu feature On 12/05/2012 09:15 PM, snmishra(a)linux.vnet.ibm.com wrote: > > Quoting Doron Fediuck <dfediuck(a)redhat.com&gt;: > >> ----- Original Message ----- >>> From: "Laszlo Hornyak" <lhornyak(a)redhat.com&gt; >>> To: "Doron Fediuck" <dfediuck(a)redhat.com&gt; >>> Cc: "engine-devel" <engine-devel(a)ovirt.org&gt; >>> Sent: Wednesday, December 5, 2012 7:14:46 PM >>> Subject: Re: [Engine-devel] host cpu feature >>> >>> >>> >>> ----- Original Message ----- >>> > From: "Doron Fediuck" <dfediuck(a)redhat.com&gt; >>> > To: "Yaniv Kaul" <ykaul(a)redhat.com&gt; >>> > Cc: "Laszlo Hornyak" <lhornyak(a)redhat.com&gt;, "engine-devel" >>> > <engine-devel(a)ovirt.org&gt; >>> > 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.

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 Engine-devel(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel