Hi Thomas,

-----Original Message-----
From: Thomas Monjalon <redacted>
Sent: Friday, June 11, 2021 3:54 PM
To: Yigit, Ferruh <redacted>; Xia, Chenbo <redacted>
Cc: Xueming Li <redacted>; Viacheslav Ovsiienko
[off-list ref]; dev@dpdk.org; parav@nvidia.com; jgg@nvidia.com
Subject: Re: [dpdk-dev] [RFC 00/14] mlx5: support SubFunction

11/06/2021 07:14, Xia, Chenbo:

quoted

From: Thomas Monjalon <redacted>

quoted

10/06/2021 12:33, Ferruh Yigit:

quoted

On 5/27/2021 2:37 PM, Xueming Li wrote:

quoted

SubFunction [1] is a portion of the PCI device, a SF netdev has its

own

quoted

quoted

dedicated queues(txq, rxq). A SF shares PCI level resources with other
SFs and/or with its parent PCI function. Auxiliary bus is the
fundamental of SF.

This patch set introduces SubFunction support for mlx5 PMD driver
including class net, regex, vdpa and compress.

There is already an mdev patch, originated from long ago. Aren't

subfunctions

quoted

presented as mdev device? If so can't we use mdev for it?

No unfortunately that's different.
mlx5 SF is based on top of auxiliary bus in the kernel/sysfs.

Just out of curiosity:

Does SF use mdev before aux bus is introduced in kernel. I see some history
of it but am not sure: [1] seems SF was base on mdev. [2] seems BlueField
software v2.5 is using mdev for SF. I saw it yesterday and try to figure
out the history. Since you are here, guess you know something 😊

[1] https://patchwork.ozlabs.org/project/netdev/cover/20191107160448.20962-

1-parav@mellanox.com/

quoted

[2] https://docs.mellanox.com/display/BlueFieldSWv25011176/Mediated+Devices

Kernel maintainers rejected the use of mdev for this purpose
and suggested to use a real bus.
You can follow the discussion here:
https://lore.kernel.org/netdev/20191108205204.GB1277001@kroah.com/ (local)

OK. Thanks for the info.

Does Intel plan to use mdev for SF?

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/... 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).

And I also noticed that the mdev-based interface can only be used in userspace but aux-based
interface can also be used by other kernel sub-system (like for net, wrap it as netdev).

Thanks,
Chenbo

For the sake of follow-up discussion, this is the official mdev doc:
https://www.kernel.org/doc/Documentation/vfio-mediated-device.txt