Tuesday, September 10, 2019 10:46 AM, Maxime Coquelin: > Subject: Re: [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver > > 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.
Can you elaborate why specifically using virtio_vdpa PMD enables this SW relay during migration? e.g. the vdpa PMD of intel that runs on top of VF do that today as well. > > 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. It is not clear to me the interface map in such system. From what I understand the container will have virtio-user i/f and the host will have virtio i/f. then the virtio i/f can be programmed to work w/ vDPA or not. For full emulation I guess you will need to expose the netdev of the fully emulated virtio device to the container? Am trying to map when it is beneficial to use this virtio_vdpa PMD and when it is better to use the vendor specific vDPA PMD on top of VF. > > > 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
