On Wed, Feb 16, 2022 at 10:21 PM Hannes Reinecke <hare@xxxxxxx> wrote: > > On 2/16/22 15:08, Yongji Xie wrote: > > On Wed, Feb 16, 2022 at 8:06 PM Leon Romanovsky <leon@xxxxxxxxxx> wrote: > >> > >> On Wed, Feb 16, 2022 at 06:03:29PM +0800, Junji Wei wrote: > >>> > >>>> On Feb 16, 2022, at 5:48 PM, Leon Romanovsky <leon@xxxxxxxxxx> wrote: > >>>> > >>>> On Wed, Feb 16, 2022 at 04:00:53PM +0800, Junji Wei wrote: > >>>> > >>>> <...> > >>>> > >>>>>> > >>>>>> What is the use case for this virtio-rdma? Especially in context of RXE. > >>>>> > >>>>> Hmm... yes, we didn’t find one. In passthrough case we can use RXE directly. > >>>> > >>>> It doesn't sound like a good sales pitch. > >>> > >>> Maybe I misunderstanded what you mean. We mean we didn’t find a user case > >>> for virtio-rdma with passthrough net device. Do you want to know the user > >>> case for our virtio-rdma(RoCE) proposal? > >> > >> Yes, please. > >> > > > > I think one point is: when running RDMA accelerated applications in > > VM, the virtio-rdma solution should get better performance than RXE > > since it has a shorter data path (guest app -> host dpdk, bypass guest > > kernel). > > > And you can (potentially) implement RDMA functionality in the hypervisor > by 'simply' to a memcpy between guests. > (I know it's not simple. But you don't actually need RDMA hardware here > and still should be able to provide RDMA functionality to guests.) > Yes, and I think we're able to achieve that with virtio-rdma when one DPDK serves multiple VMs. > And if you look at the current RoCE CNAs they operate in exactly the > same way; there's a network interface, and _additionally_ an rdma > device. So for the OS both will be detected as distinct devices, who > just happen to run on the same PCI device. > Got it. Thanks, Yongji
