Re: [ovirt-users] feedback and questions about SR-IOV feature
Le 06/12/2016 à 13:19, Martin Polednik a écrit :
On 06/12/16 12:14 +0100, Nathanaël Blanchet wrote:
> Hello,
>
> My new 10G NICS support now SR-IOV, and I've played with this new
> feature as passthrough device, so as to reduce my host CPU consumption.
>
> At the origin, I set up a bond on both 10G PF nics.
>
> After many configurations, the only way I manage to use a VF into a
> VM, is to get out of the bond one nic.
>
> So does it mean that it is impossible to run a VM with VF with PF
> attached to a bond?
As far as I know, it's not possible to do that. The reason is that the
bond normally creates new (logical) interface, what you are doing is
assigning "part" of the bond directly to a VM and the driver within VM
isn't aware of the bond.
This is what I supposed, UI should prevent us to
create VFfrom when nic
is attached to a bond. Pencil icon should'nt appear in this case.
> Moreover, something strange happens : during the boot of the VM, the
> passthrough device gets an dhcp IP on the native vlan of the bond,
> and once finally up, the real vlan used by this device is on the
> different predifined vlan. It implies to me to reconfigure the
> network to ping something on the wanted vlan. Really crazy.
This could be explained by previous statement: bonding PFs at
hypervisor level and then assigning VFs to a VM can most likely cause
undefined behavior.
The issue is the same when the PF is not attached to a bond, so
in an
expected working situation.
> Other question is : In which case can it be useful to be able to bond
> 2 VF? UI let us to do so, but it is impossible to add any bridge on
> that virtual bond.
At hypervisor level? I believe it doesn't make sense.
I wonder this because UI
allows to do it. The same as above, user
shouldn't be allowed to bond two VFs, and not allowed to add virtual
network to a VF
If you require bond between 2 PFs, you can assign 2 VFs each from
different PF to a VM and bond them within the guest.
> Comparing to a large number of restrictions (migration and others),
> my opinion is that this feature seems to be very difficult to use in
> production...
The use case for SR-IOV is maximum performance at the cost of
convenience while still (somewhat) allowing you to scale.
> --
> Nathanaël Blanchet
>
> Supervision réseau
> Pôle Infrastrutures Informatiques
> 227 avenue Professeur-Jean-Louis-Viala
> 34193 MONTPELLIER CEDEX 5
> Tél. 33 (0)4 67 54 84 55
> Fax 33 (0)4 67 54 84 14
> blanchet(a)abes.fr
>
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--
Nathanaël Blanchet
Supervision réseau
Pôle Infrastrutures Informatiques
227 avenue Professeur-Jean-Louis-Viala
34193 MONTPELLIER CEDEX 5
Tél. 33 (0)4 67 54 84 55
Fax 33 (0)4 67 54 84 14
blanchet(a)abes.fr