From: Eric Biggers <ebiggers@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Ard Biesheuvel <ardb+git@google.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
herbert@gondor.apana.org.au, will@kernel.org,
catalin.marinas@arm.com, Kees Cook <kees@kernel.org>
Subject: Re: [PATCH 2/2] arm64/crc32: Implement 4-way interleave using PMULL
Date: Wed, 16 Oct 2024 16:24:11 +0000 [thread overview]
Message-ID: <20241016162411.GA3228925@google.com> (raw)
In-Reply-To: <CAMj1kXHDqD29TzE=2cw55qeKrnybgkYFCdy4jU_4E=OaUOkZNg@mail.gmail.com>
On Wed, Oct 16, 2024 at 09:12:41AM +0200, Ard Biesheuvel wrote:
> > I'd recommend calling the file crc32-4way.S and the functions
> > crc32*_arm64_4way(), rather than crc32-pmull.S and crc32*_pmull(). This would
> > avoid confusion with a CRC implementation that is actually based entirely on
> > pmull (which is possible).
>
> I'm well aware :-)
>
> commit 8fefde90e90c9f5c2770e46ceb127813d3f20c34
> Author: Ard Biesheuvel <ardb@kernel.org>
> Date: Mon Dec 5 18:42:27 2016 +0000
>
> crypto: arm64/crc32 - accelerated support based on x86 SSE implementation
>
> commit 598b7d41e544322c8c4f3737ee8ddf905a44175e
> Author: Ard Biesheuvel <ardb@kernel.org>
> Date: Mon Aug 27 13:02:45 2018 +0200
>
> crypto: arm64/crc32 - remove PMULL based CRC32 driver
>
> I removed it because it wasn't actually faster, although that might be
> different on modern cores.
The PMULL-based code removed by commit 598b7d41e544 was only 4-wide. On
Apple M1, a 12-wide PMULL-based CRC32 is actually faster than 4-way CRC32,
especially if the eor3 instruction from the sha3 extension is utilized.
This was not the case on non-Apple CPUs I tested (in 2022), though. 12-wide is
very wide and is a bit inconvenient, and IMO it's not worth doing in the kernel
at this point. It would be interesting to test the very latest CPUs, though.
- Eric
prev parent reply other threads:[~2024-10-16 16:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-10-15 10:41 [PATCH 0/2] arm64: Speed up CRC-32 using PMULL instructions Ard Biesheuvel
2024-10-15 10:41 ` [PATCH 1/2] arm64/lib: Handle CRC-32 alternative in C code Ard Biesheuvel
2024-10-15 10:41 ` [PATCH 2/2] arm64/crc32: Implement 4-way interleave using PMULL Ard Biesheuvel
2024-10-16 3:03 ` Eric Biggers
2024-10-16 7:12 ` Ard Biesheuvel
2024-10-16 16:24 ` Eric Biggers [this message]
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