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

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Message-ID: <20241129175023.GB1179@sol.localdomain>
Date: Fri, 29 Nov 2024 09:50:23 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Ard Biesheuvel <ardb@...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 Fri, Nov 29, 2024 at 05:16:42PM +0100, Ard Biesheuvel wrote:
> 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.

Thanks!  The template actually supports CRC-64 already (both LSB and MSB-first
variants) and I've tested it in userspace.  I just haven't wired it up to the
kernel's CRC-64 functions yet.

- Eric