[dpdk-stable] [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver

[Maxime Coquelin]

Hi Shahaf,

On 9/9/19 1:55 PM, Shahaf Shuler wrote:
> Hi Maxime, 
> 
> Thursday, August 29, 2019 11:00 AM, Maxime Coquelin:
>> Subject: [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver
>>
>> vDPA allows to offload Virtio Datapath processing by supported NICs, like
>> IFCVF for example.
>>
>> The control path has to be handled by a dedicated vDPA driver, so that it can
>> translate Vhost-user protocol requests to proprietary NICs registers
>> accesses.
>>
>> This driver is the vDPA driver for Virtio devices, meaning that Vhost-user
>> protocol requests get translated to Virtio registers accesses as per defined in
>> the Virtio spec.
>>
>> Basically, it can be used within a guest with a para-virtualized Virtio-net
>> device, or even with a full Virtio HW offload NIC directly on host.
> 
> Can you elaborate more on the use cases to use such driver? 
> 
> 1. If the underlying HW can support full virtio device, why we need to work w/ it w/ vDPA mode? Why not providing it to the VM as passthrough one?
> 2. why it is preferable to work w/ virtio device as the backend device to be used w/ vDPA v.s. working w/ the underlying HW VF?


IMHO, I see two uses cases where it can make sense to use vDPA with a
full offload HW device:
1. Live-migration support:  It makes it possible to switch to rings
   processing in SW during the migration as Virtio HH does not support
   dirty pages logging.

2. Can be used to provide a single standard interface (the vhost-user
   socket) to containers in the scope of CNFs. Doing so, the container
   does not need to be modified, whatever the HW NIC: Virtio datapath
   offload only, full Virtio offload, or no offload at all. In the
   latter case, it would not be optimal as it implies forwarding between
   the Vhost PMD and the HW NIC PMD but it would work.

> Is nested virtualization is what you have in mind?

For the para-virtualized virtio device, either nested virtualization,
or container running within the guest.

Maxime