linux-kernel - Re: [PATCH 0/6] x86: new optimized CRC functions, with VPCLMULQDQ support

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Message-ID: <CAMj1kXHPXS3r244jABjOKTEWaqWX2TYf-KA9i+J2-C3B4XxmUQ@mail.gmail.com>
Date: Fri, 29 Nov 2024 17:16:42 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 0/6] x86: new optimized CRC functions, with VPCLMULQDQ support

On Mon, 25 Nov 2024 at 05:12, Eric Biggers <ebiggers@...nel.org> wrote:
>
> This patchset is also available in git via:
>
>     git fetch https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git crc-x86-v1
>
> This patchset applies on top of my other recent CRC patchsets
> https://lore.kernel.org/r/20241103223154.136127-1-ebiggers@kernel.org/ and
> https://lore.kernel.org/r/20241117002244.105200-1-ebiggers@kernel.org/ .
> Consider it a preview for what may be coming next, as my priority is
> getting those two other patchsets merged first.
>
> This patchset adds a new assembly macro that expands into the body of a
> CRC function for x86 for the specified number of bits, bit order, vector
> length, and AVX level.  There's also a new script that generates the
> constants needed by this function, given a CRC generator polynomial.
>
> This approach allows easily wiring up an x86-optimized implementation of
> any variant of CRC-8, CRC-16, CRC-32, or CRC-64, including full support
> for VPCLMULQDQ.  On long messages the resulting functions are up to 4x
> faster than the existing PCLMULQDQ optimized functions when they exist,
> or up to 29x faster than the existing table-based functions.
>
> This patchset starts by wiring up the new macro for crc32_le,
> crc_t10dif, and crc32_be.  Later I'd also like to wire up crc64_be and
> crc64_rocksoft, once the design of the library functions for those has
> been fixed to be like what I'm doing for crc32* and crc_t10dif.
>
> A similar approach of sharing code between CRC variants, and vector
> lengths when applicable, should work for other architectures.  The CRC
> constant generation script should be mostly reusable.
>
> Eric Biggers (6):
>   x86: move zmm exclusion list into CPU feature flag
>   scripts/crc: add gen-crc-consts.py
>   x86/crc: add "template" for [V]PCLMULQDQ based CRC functions
>   x86/crc32: implement crc32_le using new template
>   x86/crc-t10dif: implement crc_t10dif using new template
>   x86/crc32: implement crc32_be using new template
>

Good stuff!

Acked-by: Ard Biesheuvel <ardb@...nel.org>

Would indeed be nice to get CRC-64 implemented this way as well, so we
can use it on both x86 and arm64.