[PATCH 0/2] arm64: csum: Add fused copy and Internet checksum

[Demian Shulhan]

> The scalar path seems like generic C code and not restricted to arm64,
> curious how that performs against existing (e.g. x86) assembly
> optimized implementation.
Depends. I think __builtin_addcll() is needed to get roughly the same
performance as the asm version. In my tests GCC on arm64 turns it
into adds + cset instead of adcs like on x86.
But I will look at it, thanks!

пн, 2 лист. 2026 р. о 12:44 saeed bishara <saeed.bishara.os at gmail.com> пише:
>
> On Sun, Nov 1, 2026 at 3:34 PM Demian Shulhan <demyansh at gmail.com> wrote:
> >
> > I would prefer to keep only the scalar version of the fused copy+csum.
> > It reads the data once instead of twice, and on real Armv9 hardware it
> > cuts end-to-end cycles/byte for bulk TCP over WireGuard by 3-12%
> > depending on the core (+6-8% throughput). It uses only general-purpose
> > registers, so there is no FPSIMD state to save and it is safe in any
> > context.
> >
> > If you are OK with the scalar path, I can send v2 with NEON dropped,
> > the scalar path only, and the KUnit fix for the x86 zero-length case
> > Jakub reported.
> >
> The scalar path seems like generic C code and not restricted to arm64,
> curious how that performs against existing (e.g. x86) assembly
> optimized implementation.
> saeed