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

From: Artur Skawina <art.08.09@gmail.com>
Date: Aug 7, 2009, 04:16 UTC
Message-ID: <4A7BAAB2.8040807@gmail.com>
In-Reply-To: <alpine.LFD.2.01.0908061909310.3390@localhost.localdomain>

Linus Torvalds wrote:

> 
> Here's the plain "linus" baseline (ie the "Do register rotation in cpp") 
> thing, with the fixed "E += TEMP .." thing):

> 	linus          0.4018       151.9

> and here it is with your patch:

> 	linus          0.4653       131.2

> (ok, so the numbers aren't horribly stable, but the "plain linus" thing 
> consistently outperforms here - and underperforms with your patch).

Well, I'd be surprised if one C version would always be the winner on every single cpu; that 13% loss[1] I think would be an acceptable compromise, if the goal is to have one implementation that does reasonably well on all cpus.

That's why i asked how the change did on nehalem; if it's a measurable loss on anything modern (core2+), then of course the P4s must suffer; and one could always blame the compiler ;) It's not like the difference in sha1 overhead will be noticeable in normal git use.

artur

[1] I suspect the old gcc is a factor (4.0.4 does <100M/s here).