Re: x86 SHA1: Faster than OpenSSL

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, 6 Aug 2009, Artur Skawina wrote:
> 
> #             TIME[s] SPEED[MB/s]
> rfc3174         1.357       44.99
> rfc3174         1.352       45.13
> mozilla         1.509       40.44
> mozillaas       1.133       53.87
> linus          0.5818       104.9
> 
> so it's more than twice as fast as the mozilla implementation.

So that's some general SHA1 benchmark you have?

I hope it tests correctness too. 

Although I can't imagine it being wrong - I've made mistakes (oh, yes, 
many mistakes) when trying to convert the code to something efficient, and 
even the smallest mistake results in 'git fsck' immediately complaining 
about every single object.

But still. I literally haven't tested it any other way (well, the git 
test-suite ends up doing a fair amount of testing too, and I _have_ run 
that).

As to my atom testing: my poor little atom is a sad little thing, and 
it's almost painful to benchmark that thing. But it's worth it to look at 
how the 32-bit code compares to the openssl asm code too:

 - BLK_SHA1:

	real	2m27.160s
	user	2m23.651s
	sys	0m2.392s

 - OpenSSL:

	real	2m12.580s
	user	2m9.998s
	sys	0m1.811s

 - Mozilla-SHA1:

	real	3m21.836s
	user	3m18.369s
	sys	0m2.862s

As expected, the hand-tuned assembly does better (and by a bigger margin). 
Probably partly because scheduling is important when in-order, and partly 
because gcc will have a harder time with the small register set.

But it's still a big improvement over mozilla one.

(This is, as always, 'git fsck --full'. It spends about 50% on that SHA1 
calculation, so the SHA1 speedup is larger than you see from just th 
enumbers)

		Linus