Tuesday, September 10, 2019 4:56 PM, Maxime Coquelin: > Subject: Re: [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver > On 9/10/19 3:44 PM, Shahaf Shuler wrote: > > Tuesday, September 10, 2019 10:46 AM, Maxime Coquelin: > >> Subject: Re: [dpdk-dev] [PATCH 00/15] Introduce Virtio vDPA driver
[...] > >> > >> Hi Shahaf, > >> > >> > >> 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. > > I think there were a misunderstanding. When I said: > " > I see two uses cases where it can make sense to use vDPA with a full offload > HW device " > > I meant, I see two uses cases where it can make sense to use vDPA with a full > offload HW device, instead of the full offload HW device to use Virtio PMD. > > In other words, I think it is preferable to only offload the datapath, so > that it > is possible to support SW live-migration. > > >> > >> 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. > > I think that with above clarification, I made it clear that the goal of this > driver > is not to replace vendors vDPA drivers (their control path maybe not even be > compatible), but instead to provide a generic driver that can be used either > within a guest with a para-virtualized Virtio- net device or with HW NIC that > fully offloads Virtio (both data and control paths). Thanks Maxim, It is clearer now. From what I understand this driver is to be used w/ vDPA when the underlying device is virtio. I can perfectly understand the para-virt ( + nested virtualization / container inside VM) use case. Regarding the fully emulated virtio device on the host (instead of a plain VF) - for me the benefit still not clear - if you have HW that can expose VF why not use VF + vendor specific vDPA driver. Anyway - for the series, Acked-by: Shahaf Shuler <shah...@mellanox.com>
