[Engine-devel] host cpu feature

[snmishra at linux.vnet.ibm.com]

Quoting Doron Fediuck <dfediuck at redhat.com>:

> ----- Original Message -----
>> From: "Laszlo Hornyak" <lhornyak at redhat.com>
>> To: "Doron Fediuck" <dfediuck at redhat.com>
>> Cc: "engine-devel" <engine-devel at ovirt.org>
>> Sent: Wednesday, December 5, 2012 7:14:46 PM
>> Subject: Re: [Engine-devel] host cpu feature
>>
>>
>>
>> ----- Original Message -----
>> > From: "Doron Fediuck" <dfediuck at redhat.com>
>> > To: "Yaniv Kaul" <ykaul at redhat.com>
>> > Cc: "Laszlo Hornyak" <lhornyak at redhat.com>, "engine-devel"
>> > <engine-devel at ovirt.org>
>> > 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.

Regards
Sharad Mishra

> _______________________________________________
> Engine-devel mailing list
> Engine-devel at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/engine-devel