Re: [dpdk-dev] [RFC 00/14] mlx5: support SubFunction

["Xia, Chenbo" <chenbo.xia@intel.com>]

Hi Parav,

> -----Original Message-----
> From: Parav Pandit <parav@nvidia.com>
> Sent: Tuesday, June 15, 2021 1:43 PM
> To: Xia, Chenbo <chenbo.xia@intel.com>; NBU-Contact-Thomas Monjalon
> <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: Xueming(Steven) Li <xuemingl@nvidia.com>; Slava Ovsiienko
> <viacheslavo@nvidia.com>; dev@dpdk.org; Jason Gunthorpe <jgg@nvidia.com>
> Subject: RE: [dpdk-dev] [RFC 00/14] mlx5: support SubFunction
> 
> 
> 
> > From: Xia, Chenbo <chenbo.xia@intel.com>
> > Sent: Tuesday, June 15, 2021 11:03 AM
> >
> > Hi Parav,
> >
> > > -----Original Message-----
> > > From: Parav Pandit <parav@nvidia.com>
> > > Sent: Tuesday, June 15, 2021 12:05 PM
> > > To: Xia, Chenbo <chenbo.xia@intel.com>; NBU-Contact-Thomas Monjalon
> > > <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@intel.com>
> > > Cc: Xueming(Steven) Li <xuemingl@nvidia.com>; Slava Ovsiienko
> > > <viacheslavo@nvidia.com>; dev@dpdk.org; Jason Gunthorpe
> > > <jgg@nvidia.com>
> > > Subject: RE: [dpdk-dev] [RFC 00/14] mlx5: support SubFunction
> > >
> > > Hi Chenbo,
> > >
> > > > From: Xia, Chenbo <chenbo.xia@intel.com>
> > > > Sent: Tuesday, June 15, 2021 7:41 AM
> > > >
> > > > Hi Thomas,
> > > >
> > > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > Sent: Friday, June 11, 2021 3:54 PM
> > > [..]
> > >
> > > >
> > > > Yes. In our term it's called Assignable Device Interface (ADI)
> > > > introduced in Intel Scalable IOV
> > > > (https://01.org/blogs/2019/assignable-interfaces-intel-
> > > > scalable-i/o-virtualization-linux)
> > > >
> > > > And vfio-mdev is chosen to be the software framework for it. I start
> > > > to
> > > realize
> > > > there is difference between SF and ADI: SF considers multi-function
> > > > devices which may include net/regex/vdpa/...
> > > Yes. net, rdma, vdpa, regex ++.
> > > And eventually vfio_device to map to VM too.
> > >
> > > Non mdev framework is chosen so that all the use cases of kernel only,
> > > or user only or mix modes can be supported.
> >
> > OK. Got it.
> >
> > >
> > > > But ADI only focuses on the
> > > > virtualization of the devices and splitting devices to logic parts
> > > > and
> > > providing
> > > > huge number of interfaces to host APP. I think SF also considers
> > > > this but is mainly used for multi-function devices (like DPU in your
> term?
> > > > Correct me if I'm wrong).
> > > >
> > > SF also supports DPU mode too but it is in addition to above use cases.
> > > SF will expose mdev (or a vfio_device) to map to a VM.
> >
> > So your SW actually supports vfio-mdev? I suppose the device-specific mdev
> > Kernel module is out-of-tree?
> >
> mlx5 driver doesn't support vfio_device for SFs.
> Kernel plumbing for PASID assignment to SF is WIP currently kernel community.
> We do not have any out-of-tree kernel module.
> 
> > Just FYI:
> >
> > We are introducing a new mdev bus for DPDK:
> > http://patchwork.dpdk.org/project/dpdk/cover/20210601030644.3318-1-
> > chenbo.xia@intel.com/
> >
> I am yet to read about it. But I am not sure what value does it add.
> A user can open a vfio device using vfio subsystem and operate on it.
> A vfio device can be a create as a result of binding PCI VF/PF to vfio-pci
> driver or a SF by binding SF to vfio_foo driver.

Yes, in general it is the way. For vfio-mdev, it works as binding the vfio-mdev
to parent device and echo uuid to create a virtual device. VFIO APP like DPDK,
as you said, should work similar with VFIO UAPI for vfio-pci devices or mdev-based
devices. But currently DPDK only cares about vfio-pci devices and does not care
things for other cases like mdev-based pci devices. For example, it does not scan
/sys/bus/mdev and it always uses pci bdf as device address, which mdev-based pci
devices do not have. Therefore I sent that patchset.

> There is kernel work in progress to use vfio core as library.

OK. Could you share me some link to it? Much appreciated.

> So we do not anticipate to use add mdev layer and uuid to create a vfio device
> for a SF.

OK. For now, we are following the vfio-mdev standard, using UUID to create vfio
devices.

> 
> For Intel, ADI will never has any netdevs or rdma dev?

I think technically it could have. But for some devices like our dma devices, it's
just using mdev:

https://www.spinics.net/lists/kvm/msg244417.html

Thanks,
Chenbo