[Cake] Re: flow_hash_from_keys_small?

[Tom Herbert <tom@herbertland.com>]

Hi Dave,

"Hi all" is not needed in cover letter. I suggest that you make a splash by
announcing what the perf improvement is.

You send send this as RFC on netdev list (May or may not get any comments)

Tom




On Mon, May 25, 2026, 8:46 AM dave seddon <dave.seddon.ca@gmail.com> wrote:

> G'day,
>
> Here are a couple of patches that make cake ever so slightly faster.
>
> Longer
> For the last few months, I've been working on Tom's xdp2 project,
> comparing the performance of the kernel's existing flow dissector versus
> what xdp2 (c/c++) and a xdp2-rs (rust) can produce.
>
> For real world performance tests the lab has x2 pairs of machines:
> - AMD Ryzen 5 PRO 2400G CPU with Intel X710
> - AMD Ryzen 5 PRO 2400G CPU with ConnectX-4 Lx
>
> After extensive analysis, I compared the flow metadata between the kernel
> and xdp2, and found that simplifying the flow hash yields a small
> performance improvement.  I have NOT tested this on Intel CPUs.
>
> The kernel used for the performance testing is
> [das@hp1:~]$ uname -a Linux hp1 7.1.0-rc4 #1-NixOS SMP PREEMPT_DYNAMIC
> Tue Jan 1 00:00:00 UTC 1980 x86_64 GNU/Linux
>
>
> The draft letter for the kernel network mailing list, which describes the
> changes, is here:
>
>
> https://github.com/randomizedcoder/xdp2/blob/flow-keys-compat-reorder/kernel-patches/series1-flow-hash-small/v1/0000-cover-letter.patch
>
>
> Documentation patch
>
> https://github.com/randomizedcoder/xdp2/blob/flow-keys-compat-reorder/kernel-patches/series1-flow-hash-small/v1/0001-Documentation-networking-add-flow_dissector-consumer.patch
>
>
> Patches
>
> https://github.com/randomizedcoder/xdp2/blob/flow-keys-compat-reorder/kernel-patches/series1-flow-hash-small/v1/0002-net-flow_dissector-add-flow_hash_from_keys_small-5-t.patch#L82
>
>
> https://github.com/randomizedcoder/xdp2/blob/flow-keys-compat-reorder/kernel-patches/series1-flow-hash-small/v1/0003-net-sched-sch_cake-use-flow_hash_from_keys_small-for.patch#L50
>
> I'm interested in any feedback, particularly regarding the naming
> "flow_hash_from_keys_small".
>
> Thanks in advance
>
> --
> Regards,
> Dave Seddon
> +1 415 857 5102
>