[RFC 00/27] Add VDUSE support to Vhost library

[Xia, Chenbo]

> -----Original Message-----
> From: Morten Brørup <mb at smartsharesystems.com>
> Sent: Thursday, April 13, 2023 3:41 AM
> To: Maxime Coquelin <maxime.coquelin at redhat.com>; Ferruh Yigit
> <ferruh.yigit at amd.com>; dev at dpdk.org; david.marchand at redhat.com; Xia,
> Chenbo <chenbo.xia at intel.com>; mkp at redhat.com; fbl at redhat.com;
> jasowang at redhat.com; Liang, Cunming <cunming.liang at intel.com>; Xie, Yongji
> <xieyongji at bytedance.com>; echaudro at redhat.com; eperezma at redhat.com;
> amorenoz at redhat.com
> Subject: RE: [RFC 00/27] Add VDUSE support to Vhost library
> 
> > From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
> > Sent: Wednesday, 12 April 2023 17.28
> >
> > Hi Ferruh,
> >
> > On 4/12/23 13:33, Ferruh Yigit wrote:
> > > On 3/31/2023 4:42 PM, Maxime Coquelin wrote:
> > >> This series introduces a new type of backend, VDUSE,
> > >> to the Vhost library.
> > >>
> > >> VDUSE stands for vDPA device in Userspace, it enables
> > >> implementing a Virtio device in userspace and have it
> > >> attached to the Kernel vDPA bus.
> > >>
> > >> Once attached to the vDPA bus, it can be used either by
> > >> Kernel Virtio drivers, like virtio-net in our case, via
> > >> the virtio-vdpa driver. Doing that, the device is visible
> > >> to the Kernel networking stack and is exposed to userspace
> > >> as a regular netdev.
> > >>
> > >> It can also be exposed to userspace thanks to the
> > >> vhost-vdpa driver, via a vhost-vdpa chardev that can be
> > >> passed to QEMU or Virtio-user PMD.
> > >>
> > >> While VDUSE support is already available in upstream
> > >> Kernel, a couple of patches are required to support
> > >> network device type:
> > >>
> > >> https://gitlab.com/mcoquelin/linux/-/tree/vduse_networking_poc
> > >>
> > >> In order to attach the created VDUSE device to the vDPA
> > >> bus, a recent iproute2 version containing the vdpa tool is
> > >> required.
> > >
> > > Hi Maxime,
> > >
> > > Is this a replacement to the existing DPDK vDPA framework? What is the
> > > plan for long term?
> > >
> >
> > No, this is not a replacement for DPDK vDPA framework.
> >
> > We (Red Hat) don't have plans to support DPDK vDPA framework in our
> > products, but there are still contribution to DPDK vDPA by several vDPA
> > hardware vendors (Intel, Nvidia, Xilinx), so I don't think it is going
> > to be deprecated soon.
> 
> Ferruh's question made me curious...
> 
> I don't know anything about VDUSE or vDPA, and don't use any of it, so
> consider me ignorant in this area.
> 
> Is VDUSE an alternative to the existing DPDK vDPA framework? What are the
> differences, e.g. in which cases would an application developer (or user)
> choose one or the other?

Maxime should give better explanation.. but let me just explain a bit.

Vendors have vDPA HW that support vDPA framework (most likely in their DPU/IPU
products). This work is introducing a way to emulate a SW vDPA device in
userspace (DPDK), and this SW vDPA device also supports vDPA framework.

So it's not an alternative to existing DPDK vDPA framework :)

Thanks,
Chenbo

> 
> And if it is a better alternative, perhaps the documentation should
> mention that it is recommended over DPDK vDPA. Just like we started
> recommending alternatives to the KNI driver, so we could phase it out and
> eventually get rid of it.
> 
> >
> > Regards,
> > Maxime