linux-kernel - Re: [PATCH 00/13] lib/crc: improve how arch-optimized code is integrated

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Message-ID: <20250608234646.GE1259@sol>
Date: Sun, 8 Jun 2025 16:46:46 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
	linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
	x86@...nel.org, linux-arch@...r.kernel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	"Jason A . Donenfeld " <Jason@...c4.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/13] lib/crc: improve how arch-optimized code is
 integrated

On Sun, Jun 01, 2025 at 03:44:28PM -0700, Eric Biggers wrote:
> This series improves how lib/crc supports arch-optimized code.  First,
> instead of the arch-optimized CRC code being in arch/$(SRCARCH)/lib/, it
> will now be in lib/crc/$(SRCARCH)/.  Second, the API functions (e.g.
> crc32c()), arch-optimized functions (e.g. crc32c_arch()), and generic
> functions (e.g. crc32c_base()) will now be part of a single module for
> each CRC type, allowing better inlining and dead code elimination.  The
> second change is made possible by the first.
> 
> As an example, consider CONFIG_CRC32=m on x86.  We'll now have just
> crc32.ko instead of both crc32-x86.ko and crc32.ko.  The two modules
> were already coupled together and always both got loaded together via
> direct symbol dependency, so the separation provided no benefit.
> 
> Note: later I'd like to apply the same design to lib/crypto/ too, where
> often the API functions are out-of-line so this will work even better.
> In those cases, for each algorithm we currently have 3 modules all
> coupled together, e.g. libsha256.ko, libsha256-generic.ko, and
> sha256-x86.ko.  We should have just one, inline things properly, and
> rely on the compiler's dead code elimination to decide the inclusion of
> the generic code instead of manually setting it via kconfig.
> 
> Having arch-specific code outside arch/ was somewhat controversial when
> Zinc proposed it back in 2018.  But I don't think the concerns are
> warranted.  It's better from a technical perspective, as it enables the
> improvements mentioned above.  This model is already successfully used
> in other places in the kernel such as lib/raid6/.  The community of each
> architecture still remains free to work on the code, even if it's not in
> arch/.  At the time there was also a desire to put the library code in
> the same files as the old-school crypto API, but that was a mistake; now
> that the library is separate, that's no longer a constraint either.
> 
> Patches 1 and 2, which I previously sent out by themselves, are
> prerequisites because they eliminate the need for the CRC32 library API
> to expose the generic functions.
> 
> Eric Biggers (13):
>   crypto/crc32: register only one shash_alg
>   crypto/crc32c: register only one shash_alg

Applied the first 2 patches to
https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=crc-next

The remaining patches have new versions in the v2 series.

- Eric