Re: mlx5 AF_XDP zero-copy queues

[Jakub Kicinski <kuba@kernel.org>]

On Sat, 13 Jul 2024 12:23:31 +0530 Srivats P wrote:
> I'm seeing a behaviour difference between kernel 5.4 and 5.15 wrt the
> AF_XDP queues used for zero copy. This is specific to the mlx5.
> 
> Assume you have 'n' queues configured on the interface.
> 
> In 5.4, you had to use n to 2*n -1 queue numbers for AF_XDP zc. Using
> 0 to n-1 queues would use copy mode.
> 
> In 5.15, you have to use 0 to n-1 for zero copy also. Socket creation
> fails if you use queue >=n.
> 
> Also, with 5.4 netdev stats would not be incremented for AF_XDP
> packets whereas with 5.15 they do get incremented?
> 
> Can someone confirm this behaviour change or point me to relevant
> mailing list discussions or some other information on the same? My
> google-fu is failing me.
> 
> When did this change go into the kernel? I can't find anything in the
> kernelnewbies.org changelog between 5.4 and 5.15.

Hm, can't find the relevant commit quickly either now. But it's
intentional. The new behavior is how all other drivers work.
Hopefully this change isn't a deal breaker for anyone because
long term the lack of uniformity among drivers is a PITA.