Re: [PATCH bpf v2] xsk: Do not free ZC Rx buffer when the Rx ring is full

[Jerome Tollet <jerome.tollet@gmail.com>]

Hi Marcin,

I tested this patch on a ConnectX-5 (firmware 16.26.1040) with
AF_XDP zero-copy. Both test kernels include my earlier mlx5e fixes,
e01620844c5c and 63811edf5125. The only source difference between
them is this v2 patch.

The receiver deliberately stopped consuming the RX ring for two
seconds while continuing to supply FQ buffers. Each run recorded
roughly 1.8–2.6 million RX-ring-full events.

With striding RQ enabled, the kernel without this patch reported
225 RX frame ownership errors immediately after consumption resumed.
I reproduced this with need_wakeup both enabled and disabled. With
this patch, both runs completed 15 seconds and received over
15 million packets without an ownership error.

With cyclic RQ, neither kernel reported an ownership error under
the same test. This is consistent with my earlier cyclic reproducer,
which was fixed by the mlx5e change alone.

So this test shows a remaining striding-RQ failure despite both mlx5e
fixes, and confirms that this patch resolves it on my CX5.

Thanks,
Jerome