netdev - Re: [PATCH 1/3] sha512: make it work, undo percpu message schedule

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Date:	Sat, 14 Jan 2012 13:52:11 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	ken@...elabs.ch, Steffen Klassert <steffen.klassert@...unet.com>,
	security@...nel.org
Subject: Re: [PATCH 1/3] sha512: make it work, undo percpu message schedule

On Sat, Jan 14, 2012 at 1:46 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> This is too risky, and we provided an alternate patch, not just for fun.

Did you see the second patch?

The one that got rid of the *stupid* 80-entry array?

I don't know why so many sha implementations do that idiotic full
array, when the circular one is much better.

In fact, the 16-entry circular array allows machines with lots of
registers to keep all the state in registers and the C implementation
can often be as good as hand-tuned assembly. At least that's true for
sha1, I'm not sure you can do the same with sha512.

But that actually *requires* that the 16-entry array be done on the
stack as an automatic array. Anything else, and the compiler won't be
able to do it.

                       Linus
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