Re: [dpdk-dev] [PATCH v4 00/44] net/virtio: Virtio PMD rework

[Ilya Maximets <i.maximets@ovn.org>]

On 2/1/21 2:16 PM, Maxime Coquelin wrote:
> Hi Ilya,
> 
> On 2/1/21 2:03 PM, Ilya Maximets wrote:
>> CC: ovs-dev
>>
>> On 2/1/21 2:00 PM, Ilya Maximets wrote:
>>> On 1/26/21 11:15 AM, Maxime Coquelin wrote:
>>>>
>>>> Only functionnal change in this second part is making the
>>>> Vhost-user server mode blocking at init time, as long as
>>>> a client is not connected. The goal of this change is to
>>>> make the Vhost-user support much more robust, as without
>>>> blocking, the driver has to assume features that are going
>>>> to be supported by the client, which is very fragile and
>>>> error prone. As a side-effect, it also simplifies the
>>>> logic nin several place of the virtio-user PMD.
>>>
>>> Hi, Maxime.
>>>
>>> I didn't actually look at the code, but I have a question.
>>> Does above text mean that with this change OVS will hang inside
>>> driver_register() or similar function until client is connected
>>> to dpdkvhostuser (server mode) port?
>>>
>>> If so, I think, we will not be able to support server mode
>>> in OVS anymore and will have to actually remove it.  It's
>>> deprecated for a long time now, but I think it might still be in
>>> use by some people, especially for virtio-user usecase.
> 
> No, there is no impact for OVS. My explanation was maybe a bit
> confusion, sorry about that.
> 
> I meant that Virtio-user PMD, acting as Vhost-user master in server
> mode, will be blocking waiting for client (OVS dpdkvhostuserclient in
> your case) connection. This makes the Virtio-user PMD in server mode to
> behave the same as QEMU Vhost-user port in server mode.

Oh.  OK.  So the only affected party is 'net_virtio_user' PMD and vhost
library is not affected, right?

And in this case the following command will block OVS:

  ovs-vsctl add-port br0 vu -- set Interface vu type=dpdk \
      options:dpdk-devargs="net_virtio_user,path=vu.sock,server=1"

Is that correct?

(I'm not sure if this works right now, though.  I didn't test it.)


> 
> Only noticeable effect on OVS side should be more reliability, as
> without this change, Virtio-user PMD could assume OVS Vhost-user backend
> would support features before the connection happens.
> 
>>> Best regards, Ilya Maximets.
>>>
>>
> 
> Regards,
> Maxime
>