[Engine-devel] host cpu feature

[Dan Kenigsberg]

On Wed, Dec 05, 2012 at 08:39:52AM -0500, Laszlo Hornyak wrote:
> 
> 
> ----- Original Message -----
> > From: "Dan Kenigsberg" <danken at redhat.com>
> > To: "Laszlo Hornyak" <lhornyak at redhat.com>
> > Cc: "Yaniv Kaul" <ykaul at redhat.com>, "engine-devel" <engine-devel at ovirt.org>
> > Sent: Wednesday, December 5, 2012 1:55:19 PM
> > Subject: Re: [Engine-devel] host cpu feature
> > 
> > On Wed, Dec 05, 2012 at 06:46:09AM -0500, Laszlo Hornyak wrote:
> > > 
> > > 
> > > ----- Original Message -----
> > > > From: "Yaniv Kaul" <ykaul at redhat.com>
> > > > To: "Laszlo Hornyak" <lhornyak at redhat.com>
> > > > Cc: "engine-devel" <engine-devel at ovirt.org>
> > > > Sent: Wednesday, December 5, 2012 12:23:47 PM
> > > > Subject: Re: [Engine-devel] host cpu feature
> > > > 
> > > > On 12/05/2012 12:32 PM, Laszlo Hornyak wrote:
> > > > > Hi,
> > > > >
> > > > > CPU-Host support allows the virtual machines to see and utilize
> > > > > the
> > > > > host's CPU flags, this enables better performance in VM's, at
> > > > > the
> > > > > price of worse portablity.
> > > > >
> > > > > http://www.ovirt.org/Features/Cpu-host_Support
> > > > >
> > > > > Your feedback is welcome!
> > > > >
> > > > > Thank you,
> > > > > Laszlo
> > > > > _______________________________________________
> > > > > Engine-devel mailing list
> > > > > Engine-devel at ovirt.org
> > > > > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > > > 
> > > > - I assume that when you allow migration, you'd use host-model?
> > > > This
> > > > is
> > > > not clear from the design. It seems like we VDSM developers can
> > > > choose
> > > > to use either this or passthrough, while in practice we should
> > > > support both.
> > 
> > I join Kaul's question: it is an ovirt-level question whether
> > hostPassthrough or hostModel or both should be supported. It should
> > not
> > be a unilateral vdsm decision.
> 
> Ah, possibly misunderstanding, I did not mean that VDSM should decide whether to use host-passthrough or host-model. The engine should decide.
> I meant _you_ should decide which version of vdsm api modification do you want :)
> 
> > 
> > > 
> > > If AllowMigrateCPUHost is set to true (in case you have the same
> > > cpu model everywhere in your DC) migration of such hsots will be
> > > enabled. Otherwise it will not be enabled.
> > 
> > What is the breadth of AllowMigrateCPUHost? Engine wide? Per DC? Per
> > cluster?
> 
> I thought of eninge-wide. The of course you can have different models in two different DC, but they should be unique in one.
> We can add this to DC or cluster level, imho it would be just another checkbox on the UI that most users would not use.

Most users are not going to use hostcpu. This feature is intended to
people who have performance-critical VMs, and a set of hosts that can
run them. These very same people may have less critical desktops that
are to be allowed to run on any host.