Re: [RFC v2 5/9] vhost-vdpa: implement vhost-vdpa backend

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, May 25, 2020 at 4:34 PM Cindy Lu <lulu@redhat.com> wrote:
> On Thu, May 21, 2020 at 8:40 PM Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > On Sat, May 09, 2020 at 12:32:14AM +0800, Cindy Lu wrote:
> > > From: Tiwei Bie <tiwei.bie@intel.com>
> > >
> > > Currently we have 2 types of vhost backends in QEMU: vhost kernel and
> > > vhost-user. The above patch provides a generic device for vDPA purpose,
> > > this vDPA device exposes to user space a non-vendor-specific configuration
> > > interface for setting up a vhost HW accelerator, this patch set introduces
> > > a third vhost backend called vhost-vdpa based on the vDPA interface.
> > >
> > > Vhost-vdpa usage:
> > >
> > >   qemu-system-x86_64 -cpu host -enable-kvm \
> > >     ......
> > >   -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-id,id=vhost-vdpa0 \
> > >   -device virtio-net-pci,netdev=vhost-vdpa0,page-per-vq=on \
> >
> > I haven't looked at vDPA in depth. What is different here compared to
> > the existing vhost-backend.c kernel backend?
> >
> > It seems to be making the same ioctls calls so I wonder if it makes
> > sense to share the vhost-backend.c kernel code?
> >
> > Stefan
> Hi Stefan,
> Sorry for the late reply and Thanks for these suggestions.
> I think the most difference between vhost kernel and vdpa is vdpa
> depends on a real hardware.
> The point is that vDPA devices work as a virtio device, but vhost-vdpa
> qemu must present a vhost-like device in qemu vhost layer.
> The ioctl  calls are similar  with vhost-backend.c now, but after more
> and more NIC support vdpa. The difference between vhost-backend.c and
> vpda will become more and more big. It will make the code complicated
> to share the  code with kernel code.

Okay, thanks.

Stefan