Re: [PATCH 0/7] block-sha1: improved SHA1 hashing

Linus Torvalds wrote:

Just out of curiosity, does anything change if you change the

	B = SHA_ROR(B,2)

into a

	B = SHA_ROR(SHA_ROR(B,1),1)

instead? It's very possible that it becomes _much_ worse, but I guess it's 

Did try that yesterday, didn't help. Will recheck now.. yep:

before: linus          0.3554       171.7
after:  linus           0.407         150

still true for the current version.

So optimizing for P4 is often the wrong thing.

Secondly, P4's are going away. You may have one, but they are getting 
rare. So optimizing for them is a losing proposition in the long run.

Sure, no argument; it's just that avoiding the P4 pitfalls is usually
not that hard and the impact on other, non-netburst, archs is low.
There are a lot of P4s out there and they're not going away soon.
(i'm still keeping most of my git trees on a P3...)

For generic C code such as this the difference for your i7 was -2% and
+70% for my P4; all the other (but one, i think) optimizations which
worked on P4 also applied to 32-bit i7. As i happen to have a p4 i can
just as well test the code on it, many improvements will likely apply
to other cpus too. That's all, i doubt anybody seriously considered
"optimizing for P4"; there is a reason intel discontinued them :)

The atom is a more important target, but only the asm versions did well
there so far.

artur