On Thu, 6 Aug 2009, Linus Torvalds wrote: > > > On Thu, 6 Aug 2009, Artur Skawina wrote: > > > > Does this make any difference for you? For me it's the best one so far > > (the linusas2 number clearly shows that for me the register renaming does > > nothing; other than that the functions should be very similar) > > Nope. If anything, it's bit slower, but it might be in the noise. I > generally got 330MB/s with my "cpp renaming" on Nehalem (32-bit - the > 64-bit numbers are ~400MB/s), but with this I got 325MB/s twice in a row, > which matches the linusas2 numbers pretty exactly. I actually found a P4 I have access to, except that one is a Prescott. And I can't run it in 32-bit mode, because I only have a regular user login, and it only has the 64-bit development environment. But I can do the hacked-for-64bit sha1bench runs, and I tested your patch. It's horrible. Here's the plain "linus" baseline (ie the "Do register rotation in cpp") thing, with the fixed "E += TEMP .." thing): # TIME[s] SPEED[MB/s] rfc3174 1.648 37.03 rfc3174 1.677 36.4 linus 0.4018 151.9 linusas 0.4439 137.5 linusas2 0.4381 139.3 mozilla 0.9587 63.66 mozillaas 0.9434 64.7 and here it is with your patch: # TIME[s] SPEED[MB/s] rfc3174 1.667 36.61 rfc3174 1.644 37.12 linus 0.4653 131.2 linusas 0.4412 138.3 linusas2 0.4388 139.1 mozilla 0.9466 64.48 mozillaas 0.9449 64.59 (ok, so the numbers aren't horribly stable, but the "plain linus" thing consistently outperforms here - and underperforms with your patch). However, note that since this is the 64-bit thing, there likely aren't any spill issues, but it's simply an issue of "just how did the array[] accesses get scheduled" etc. And since this is a Prescott (or rather "Xeon") P4, the shifter isn't quite as horrible as yours is. _And_ this is a different gcc version (4.0.3). So the numbers aren't really all that comparable. It's more an example of "optimizing for P4 is futile, because you're just playing with total randomness". That's like a 20MB/s difference, just from moving a few ALU ops around a bit. And it's entirely possible that if I had gcc-4.4 on that machine, your patch would magically do the right thing ;) Sadly, that machine is just a ssh gateway, so there's no real development tools on it at all - no way to get good profiles etc. So I can't really say exactly what the problem pattern is :( Linus -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html