Re: [PATCH v2 3/3] aarch64: Optimized memchr specific to AmpereComputing skylark

[Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>]

Hi,

> Do you have numbers on much improvement this yields on skylark (using at
> least glibc own benchtests)? Also, why use 16-bytes in loop instead of
> default 32 (in your case basically unrolling the loop)? 

Since it aligns early the overhead of aligning to 32 bytes would be even higher.
The approach strlen uses (first iteration unaligned) is much faster.

> I am asking because it seems that slower neon units seems to be a common
> thing in recent chips, so one option would to instead of create a 'skylark'
> variant, we add a 'no-neon' instead.

It's likely more about unaligned access performance - even an old Cortex-A72 does
much better using the Neon version. Both memchr variants can be optimized further.
In general it seems better indeed to use "generic" and "simd" in the names rather than
obscure microarchitecture names.

Wilco