[Qemu-devel] [RFC 0/3] VirtIO RDMA

[Yuval Shaia]

Data center backends use more and more RDMA or RoCE devices and more and
more software runs in virtualized environment.
There is a need for a standard to enable RDMA/RoCE on Virtual Machines.

Virtio is the optimal solution since is the de-facto para-virtualizaton
technology and also because the Virtio specification
allows Hardware Vendors to support Virtio protocol natively in order to
achieve bare metal performance.

This RFC is an effort to addresses challenges in defining the RDMA/RoCE
Virtio Specification and a look forward on possible implementation
techniques.

Open issues/Todo list:
List is huge, this is only start point of the project.
Anyway, here is one example of item in the list:
- Multi VirtQ: Every QP has two rings and every CQ has one. This means that
  in order to support for example 32K QPs we will need 64K VirtQ. Not sure
  that this is reasonable so one option is to have one for all and
  multiplex the traffic on it. This is not good approach as by design it
  introducing an optional starvation. Another approach would be multi
  queues and round-robin (for example) between them.

Expectations from this posting:
In general, any comment is welcome, starting from hey, drop this as it is a
very bad idea, to yeah, go ahead, we really want it.
Idea here is that since it is not a minor effort i first want to know if
there is some sort interest in the community for such device.

The scope of the implementation is limited to probing the device and doing
some basic ibverbs commands. Data-path is not yet implemented. So with this
one can expect only that driver is (partialy) loaded and basic queries and
resource allocation is done.

One note regarding the patchset.
I know it is not standard to collaps patches from several repos as i did
here (qemu and linux) but decided to do it anyway so the whole picture can
be seen.

patch 1: virtio-net: Move some virtio-net-pci decl to include/hw/virtio
        This is a prelimenary patch just as a hack so i will not need to
        impelement new netdev
patch 2: hw/virtio-rdma: VirtIO rdma device
        The implementation of the device
patch 3: RDMA/virtio-rdma: VirtIO rdma driver
        The device driver

-- 
2.20.1