[ovirt-users] feedback and questions about SR-IOV feature

[Martin Polednik]

On 06/12/16 16:58 +0200, Michael Burman wrote:
>Hello Nathanael
>
>VFs are regular NICs and can be used as regular NICs.
>We are allowing to create bond from them and allowing to attach logical
>networks to them, because as long as they are not used by any VM, they can
>be used just as any other interfaces on the host.
>
>When creating bond from 2 VFs you should see the pencil icon, because you
>want to able to edit the bond.
>Vf is an interface and you can use it just as you use regular interface on
>the host.
>
>* When you create bond from 2 VFs, this VFs are no longer free and you
>can't use them to run VM
>* The same for attaching a network to VF, this VF is no longer considered
>as free VF.
>
>There is no problem about it, this is exactly how it was designed ) , you
>have to remember that as long as the VFs are not used by VM, they can be
>used as regular NICs and you can do with them everything you want.

That doesn't mean we have the right design: there is no problem in
bonding 2 VFs belonging to 2 different PFs; but every sane software
warns you if you try to bond 2 VFs from the same PF together (what do
you get by such bond?) -- this applies to both host and guest.

>
>http://www.ovirt.org/develop/release-management/features/engine/sr-iov/
>
>Regards,
>
>
>On Tue, Dec 6, 2016 at 4:23 PM, Nathanaël Blanchet <blanchet at abes.fr> wrote:
>
>>
>>
>> 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 at abes.fr
>>>>
>>>>
>>> _______________________________________________
>>>> Users mailing list
>>>> Users at ovirt.org
>>>> http://lists.ovirt.org/mailman/listinfo/users
>>>>
>>>
>>>
>> --
>> 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 at abes.fr
>>
>> _______________________________________________
>> Users mailing list
>> Users at ovirt.org
>> http://lists.ovirt.org/mailman/listinfo/users
>>
>
>
>
>-- 
>Michael Burman
>RedHat Israel, RHV-M Network QE
>
>Mobile: 054-5355725
>IRC: mburman