Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver.

Jason Gunthorpe
2020-05-09T12:21:30Z

On Fri, May 08, 2020 at 05:09:09PM -0700, Raj, Ashok wrote:
> Hi Jason
>
> On Fri, May 08, 2020 at 08:16:10PM -0300, Jason Gunthorpe wrote:
> > On Fri, May 08, 2020 at 01:47:10PM -0700, Raj, Ashok wrote:
> >
> > > Even when uaccel was under development, one of the options
> > > was to use VFIO as the transport, goal was the same i.e to keep
> > > the user space have one interface.
> >
> > I feel a bit out of the loop here, uaccel isn't in today's kernel is
> > it? I've heard about it for a while, it sounds very similar to RDMA,
> > so I hope they took some of my advice...
>
> I think since 5.7 maybe? drivers/misc/uacce. I don't think this is like
> RDMA, its just a plain accelerator. There is no connection management,
> memory registration or other things.. IB was my first job at Intel,
> but saying that i would be giving my age away :)

rdma was the first thing to do kernel bypass, all this stuff is like
rdma at some level.. I see this looks like the 'warp driver' stuff
redone

Wow, lots wrong here. Oh well.

> > putting emulation code back into them, except in a more dangerous
> > kernel location. This does not seem like a net win to me.
>
> Its not a whole lot of emulation right? mdev are soft partitioned. There is
> just a single PF, but we can create a separate partition for the guest using
> PASID along with the normal BDF (RID). And exposing a consistent PCI like
> interface to user space you get everything else for free.
>
> Yes, its not SRIOV, but giving that interface to user space via VFIO, we get
> all of that functionality without having to reinvent a different way to do it.
>
> vDPA went the other way, IRC, they went and put a HW implementation of what
> virtio is in hardware. So they sort of fit the model. Here the instance
> looks and feels like real hardware for the setup and control aspect.

VDPA and this are very similar, of course it depends on the exact HW
implementation.

Jason