linux-kernel - Re: [PATCH 00/12] crypto: sha256

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Message-ID: <aBLMi5XOQKJyJGu-@gondor.apana.org.au>
Date: Thu, 1 May 2025 09:21:15 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
	sparclinux@...r.kernel.org, linux-s390@...r.kernel.org,
	x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>,
	"Jason A . Donenfeld" <Jason@...c4.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/12] crypto: sha256 - Use partial block API

On Wed, Apr 30, 2025 at 10:45:43AM -0700, Eric Biggers wrote:
>
> As for your sha256_finup "optimization", it's an interesting idea, but
> unfortunately it slightly slows down the common case which is count % 64 < 56,
> due to the unnecessary copy to the stack and the following zeroization.  In the
> uncommon case where count % 64 >= 56 you do get to pass nblocks=2 to
> sha256_blocks_*(), but ultimately SHA-256 is serialized block-by-block anyway,
> so it ends up being only slightly faster in that case, which again is the
> uncommon case.  So while it's an interesting idea, it doesn't seem to actually
> be better.  And the fact that that patch is also being used to submit unrelated,
> more dubious changes isn't very helpful, of course.

I'm more than willing to change sha256_finup if you can prove it
with real numbers that it is worse than the single-block version.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt