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. > > But it seems to make a big difference for you. It seems to do well on P2 and P4 here, if it works for core2 this could be a good generic candidate. It only does 62% on an Atom, but the best C version so far exceeds it only by ~2%. > Btw, _what_ P4 do you have (Northwood or Prescott)? northwood > The Intel optimization manuals very much talk about avoiding rotates. And > they mention "with a CPUID signature corresponding to family 15 and model > encoding of 0, 1, or 2" specifically as being longer latency. That's > basically pre-prescott P4, I think. cpu family : 15 model : 2 model name : Intel(R) Pentium(R) 4 CPU 2.80GHz stepping : 5 > Anyway, on P4 I think you have two double-speed integer issue ports (ie > max four ops per cycle), but only one of them takes a rotate, and only in > the first half of the cycle (ie just one shift per cycle). > > And afaik, that is actually the _improved_ state in Prescott. The older > P4's didn't have a full shifter unit at all, iirc: shifts were "complex > instructions" in Northwood and weren't even single-clock. > > In Core 2, I think there's still just one shifter unit, but at least it's > as fast as all the other units. So P4 really does stand out as sucking as > far as shifts are concerned, and if you have an older P4, it will be even > worse. hmm, I might be able to try it on some old willamette, but my prescott's mobo died, so i can't verify that right now. I'll upload an updated sha1bench, maybe somebody else feels like checking... artur -- 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