linux-kernel - Re: [PATCH 1/2] crypto: x86/sha256-ni

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Date: Tue, 9 Apr 2024 19:36:50 -0400
From: Eric Biggers <ebiggers@...nel.org>
To: Stefan Kanthak <stefan.kanthak@...go.de>
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	ardb@...nel.org
Subject: Re: [PATCH 1/2] crypto: x86/sha256-ni - convert to use rounds macros

On Tue, Apr 09, 2024 at 06:52:02PM +0200, Stefan Kanthak wrote:
> "Eric Biggers" <ebiggers@...nel.org> wrote:
> 
> > +.macro do_4rounds i, m0, m1, m2, m3
> > +.if \i < 16
> > +        movdqu  \i*4(DATA_PTR), MSG
> > +        pshufb  SHUF_MASK, MSG
> > +        movdqa  MSG, \m0
> > +.else
> > +        movdqa  \m0, MSG
> > +.endif
> > +        paddd   \i*4(SHA256CONSTANTS), MSG
> 
> To load the round constant independent from and parallel to the previous
> instructions which use \m0 I recommend to change the first lines of the
> do_4rounds macro as follows (this might save 1+ cycle per macro invocation,
> and most obviously 2 lines):
> 
> .macro do_4rounds i, m0, m1, m2, m3
> .if \i < 16
>         movdqu  \i*4(DATA_PTR), \m0
>         pshufb  SHUF_MASK, \m0
> .endif
>         movdqa  \i*4(SHA256CONSTANTS), MSG
>         paddd   \m0, MSG
> ...

Yes, your suggestion looks good.  I don't see any performance difference on
Ice Lake, but it does shorten the source code.  It belongs in a separate patch
though, since this patch isn't meant to change the output.

- Eric