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Message-ID: <CAMj1kXHDo8dijRbSVuHzTddMhp4A+nc1t8AgvoENmS=DZ-kAOQ@mail.gmail.com>
Date: Fri, 25 Oct 2024 09:40:15 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-s390@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
loongarch@...ts.linux.dev, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 00/15] Wire up CRC32 library functions to arch-optimized code
On Mon, 21 Oct 2024 at 02:29, 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 crc32-lib-v1
>
> CRC32 is a family of common non-cryptographic integrity check algorithms
> that are fairly fast with a portable C implementation and become far
> faster still with the CRC32 or carryless multiplication instructions
> that most CPUs have. 9 architectures already have optimized code for at
> least some CRC32 variants; however, except for arm64 this optimized code
> was only accessible through the crypto API, not the library functions.
>
> This patchset fixes that so that the CRC32 library functions use the
> optimized code. This allows users to just use the library instead of
> the crypto API. This is much simpler and also improves performance due
> to eliminating the crypto API overhead including an indirect call. Some
> examples of updating users are included at the end of the patchset.
>
> Note: crc32c() was a weird case. It was a library function layered on
> top of the crypto API, which in turn is layered on top of the real
> library functions. So while it was easy to use, it was still subject to
> the crypto API overhead. This patchset provides CRC32C acceleration in
> the real library functions directly.
>
> The updated CRC32 library design is:
>
> - Each arch's CRC32 code (all variants) is in arch/$ARCH/lib/crc32*.
> This adopts what arm64 and riscv already did. Note, the crypto
> directory is not used because CRC32 is not a cryptographic algorithm.
>
> - Weak symbols are no longer used. Instead there are crc32*_base() and
> crc32*_arch(), and the appropriate ones are called based on the
> kconfig. This is similar to how the ChaCha20 library code works.
>
> - Each arch's CRC32 code is enabled by default when CRC32 is enabled,
> but it can now be disabled, controlled by the choice that previously
> controlled the base implementation only. It can also now be built as
> a module if CRC32 is a module too.
>
> - Instead of lots of pointless glue code that wires up each CRC32
> variant to the crypto API for each architecture, we now just rely on
> the existing shash algorithms that use the library functions.
>
> - As before, the library functions don't provide access to off-CPU
> crypto accelerators. But these appear to have very little, if any,
> real-world relevance for CRC32 which is very fast on CPUs.
>
> Future work should apply a similar cleanup to crct10dif which is a
> variant of CRC16.
>
> I tested all arches in QEMU using CONFIG_CRC32_SELFTEST and the crypto
> self-tests, except for mips which I couldn't figure out how to do.
>
> This patchset has the following dependencies on recent patches:
>
> - "crypto - move crypto_simd_disabled_for_test to lib"
> (https://lore.kernel.org/linux-crypto/20241018235343.425758-1-ebiggers@kernel.org/)
> - "crypto: x86/crc32c - jump table elimination and other cleanups"
> (https://lore.kernel.org/linux-crypto/20241014042447.50197-1-ebiggers@kernel.org/)
> - "arm64: Speed up CRC-32 using PMULL instructions"
> (https://lore.kernel.org/linux-crypto/20241018075347.2821102-5-ardb+git@google.com/)
> - "crypto: Enable fuzz testing for arch code"
> (https://lore.kernel.org/linux-crypto/20241016185722.400643-4-ardb+git@google.com/)
> - "crypto: mips/crc32 - fix the CRC32C implementation"
> (https://lore.kernel.org/linux-crypto/20241020180258.8060-1-ebiggers@kernel.org/)
>
> Everything can be retrieved from git using the command given earlier.
>
> Since this patchset touches many areas, getting it merged may be
> difficult. One option is a pull request with the whole patchset
> directly to Linus. Another is to have at least patches 1-2 and the
> above dependencies taken through the crypto tree in v6.13; then the arch
> patches can land separately afterwards, followed by the rest.
>
> Eric Biggers (15):
> lib/crc32: drop leading underscores from __crc32c_le_base
> lib/crc32: improve support for arch-specific overrides
> arm/crc32: expose CRC32 functions through lib
> loongarch/crc32: expose CRC32 functions through lib
> mips/crc32: expose CRC32 functions through lib
> powerpc/crc32: expose CRC32 functions through lib
> s390/crc32: expose CRC32 functions through lib
> sparc/crc32: expose CRC32 functions through lib
> x86/crc32: update prototype for crc_pcl()
> x86/crc32: update prototype for crc32_pclmul_le_16()
> x86/crc32: expose CRC32 functions through lib
> lib/crc32: make crc32c() go directly to lib
> ext4: switch to using the crc32c library
> jbd2: switch to using the crc32c library
> f2fs: switch to using the crc32 library
>
...
> 89 files changed, 1002 insertions(+), 2455 deletions(-)
Very nice cleanup!
For the series:
Reviewed-by: Ard Biesheuvel <ardb@...nel.org>
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