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@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
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34193 MONTPELLIER CEDEX 5
Tél. 33 (0)4 67 54 84 55
Fax  33 (0)4 67 54 84 14
blanchet@abes.fr

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34193 MONTPELLIER CEDEX 5
Tél. 33 (0)4 67 54 84 55
Fax  33 (0)4 67 54 84 14
blanchet@abes.fr

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