[ovirt-users] Mixing CPU types

[Martin Polednik]

----- Original Message -----
> From: "Matthew Trent" <Matthew.Trent at lewiscountywa.gov>
> To: "Yaniv Kaul" <ykaul at redhat.com>
> Cc: users at ovirt.org
> Sent: Wednesday, February 3, 2016 8:10:35 PM
> Subject: Re: [ovirt-users] Mixing CPU types
> 
> ?Actually it works great! It's been supported by KVM for a while now. I had
> one Proxmox cluster with a mix of AMD and Intel and migrated KVM VM's
> between them frequently. OpenStack (KVM) and VMWare support this as well.
> 
> 
> The trick is to expose a virtual CPU with a common set of features to the
> VMs. KVM handles the rest. From the KVM FAQ:
> 
> http://www.linux-kvm.org/page/FAQ#Does_KVM_support_live_migration_from_an_AMD_host_to_an_Intel_host_and_back.3F

That is pretty much what libvirt does. The sandy-bridge, haswell and other
cpu's that we expose are not really a CPUs, but sets of flags (called
baseline CPUs in libvirt's terminology).

Afaik there should be no issue running cluster with both CPU vendors,
the problem is lack of testing on devel side as we mostly run
single vendor clusters everywhere.
 
> "Does KVM support live migration from an AMD host to an Intel host and back?
> 
> 
> Yes. There may be issues on 32-bit Intel hosts which don't support NX (or
> XD), but for 64-bit hosts back and forth migration should work well.
> Migration of 32-bit guests should work between 32-bit hosts and 64-bit
> hosts. If one of your hosts does not support NX, you may consider disabling
> NX when starting the guest on a NX-capable system. You can do it by passing
> "-cpu qemu64,-nx" parameter to the guest."
> 
> --
> Matthew Trent
> Network Engineer
> Lewis County IT Services
> 360.740.1247 - Helpdesk
> 360.740.3343 - Direct line
> ________________________________
> From: Yaniv Kaul <ykaul at redhat.com>
> Sent: Tuesday, February 2, 2016 2:17 PM
> To: Matthew Trent
> Cc: users at ovirt.org
> Subject: Re: [ovirt-users] Mixing CPU types
> 
> 
> 
> On Mon, Feb 1, 2016 at 9:13 PM, Matthew Trent
> <Matthew.Trent at lewiscountywa.gov<mailto:Matthew.Trent at lewiscountywa.gov>>
> wrote:
> Though our new oVirt setup is better in most ways, cross-CPU-type migration
> is one of the features I miss from Proxmox. KVM supports mixed-CPU migration
> for a while now, even between AMD and Intel.
> 
> http://www.linux-kvm.org/page/Migration
> 
> I highly doubt the above works in real life scenarios.
> Y.
> 
> 
> 
> I'm using a bunch of re-purposed servers with a mix of AMD and Intel. I
> separate them into clusters, as noted, but it sure would be nice to be able
> to live migrate between them. :)
> 
> --
> Matthew Trent
> Network Engineer
> Lewis County IT Services
> 
> > Hi Rene,
> >
> > Thank you very much for coming back to me.
> >
> > That's perfect then and answers my questions exactly.
> >
> > Much appreciated.
> >
> > Regards.
> >
> >Neil Wilson.
> >
> >
> >On Wed, Jan 27, 2016 at 1:57 PM, René Koch <rkoch at
> >rk-it.at<http://rk-it.at>> wrote:
> >>
> >> Hi Neil,
> >>
> >> You can mix cpu types (but not AMD and Intel) if you leave the cluster
> >> level at the lowest cpu level.
> >> I personally don't mix cpu levels if possible, but instead create own
> >> clusters for each cpu type in order to be able to use the newest cpu
> >> features...
> >>
> >>
> >> Regards,
> >> René
> >>
> >>
> >> On 01/27/2016 12:53 PM, Neil wrote:
> >>
> >> Hi guys,
> >>
> >> I currently have an oVirt 3.5 cluster with Sandy Bridge Xeon CPU's, and I
> >> need to add a new host for more RAM and vCPU's, however the new Xeon e5
> >> cpu's are Haswell based.
> >>
> >> Can I mix CPU types (Haswell and Sandy Bridge) in my cluster and will I be
> >> able to migrate between my hosts?
> >>
> >> I'm guessing that for this to work I'll need to leave my "CPU type" set to
> >> Sandy Bridge, will the Haswell based CPU be compatible with my cluster,
> >> but
> >> just run without any Haswell type features?
> >>
> >> Apologies if this is a dumb question or if it's been answered before.
> >>
> >> Thank you.
> >>
> >> Regards.
> >>
> >> Neil Wilson
> >>
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