Re: [PATCH] Hex-coding optimizations using SVE on ARM.

On Mon, Sep 22, 2025 at 03:05:44PM -0500, Nathan Bossart wrote:
> I was able to improve the hex_decode() implementation a bit.

I took a closer look at how hex_decode() performs with smaller inputs.
There are some small regressions, so I tried fixing them by adding the
following to the beginning of the function:

if (likely(tail_idx == 0))
return hex_decode_safe_scalar(src, len, dst, escontext);

This helped a little, but it mostly just slowed things down for larger
inputs on AArch64:

arm
buf | HEAD | patch | fix
-------+-------+-------+-------
2 | 4 | 6 | 4
4 | 6 | 7 | 7
8 | 8 | 8 | 8
16 | 11 | 12 | 11
32 | 18 | 5 | 6
64 | 38 | 7 | 8
256 | 134 | 18 | 24
1024 | 514 | 67 | 100
4096 | 2072 | 280 | 389
16384 | 8409 | 1126 | 1537
65536 | 34704 | 4498 | 6128

x86
buf | HEAD | patch | fix
-------+-------+-------+-------
2 | 2 | 2 | 2
4 | 3 | 3 | 3
8 | 4 | 4 | 4
16 | 8 | 9 | 8
32 | 23 | 5 | 5
64 | 37 | 7 | 7
256 | 122 | 24 | 24
1024 | 457 | 91 | 92
4096 | 1798 | 357 | 358
16384 | 7161 | 1411 | 1416
65536 | 28621 | 5630 | 5653

I didn't do this test for hex_encode(), but I'd expect it to follow a
similar pattern. I'm tempted to suggest that these regressions are within
tolerable levels and to forge on with v10. In any case, IMHO this patch is
approaching committable quality, so I'd be grateful for any feedback.

--
nathan