linux-kernel - Re: [GIT PULL] CRC updates for 6.14

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Message-ID: <20250123140744.GB3875121@mit.edu>
Date: Thu, 23 Jan 2025 09:07:44 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>, Chao Yu <chao@...nel.org>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Vinicius Peixoto <vpeixoto@...amp.dev>,
        WangYuli <wangyuli@...sls0nwwnnilyahiblcmlmlcaoki5s.yundunwaf1.com>
Subject: Re: [GIT PULL] CRC updates for 6.14

On Wed, Jan 22, 2025 at 11:46:18PM -0800, Eric Biggers wrote:
> 
> Actually, I'm tempted to just provide slice-by-1 (a.k.a. byte-by-byte) as the
> only generic CRC32 implementation.  The generic code has become increasingly
> irrelevant due to the arch-optimized code existing.  The arch-optimized code
> tends to be 10 to 100 times faster on long messages.

Yeah, that's my intuition as well; I would think the CPU's that
don't have a CRC32 optimization instruction(s) would probably be the
most sensitive to dcache thrashing.

But given that Geert ran into this on m68k (I assume), maybe we could
have him benchmark the various crc32 generic implementation to see if
we is the best for him?  That is, assuming that he cares (which he
might not. :-).

						- Ted