[Cake] flow_hash_from_keys_small?

[Cake] flow_hash_from_keys_small?

[dave seddon]

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

[Cake] Re: flow_hash_from_keys_small?

[Tom Herbert]

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
>