On Nov 16, 2007 6:46 AM, erik quanstrom <[EMAIL PROTECTED]> wrote: > > Per your second a), performance does often improve quite a bit with 2x > > the general purpose registers. > > > > do you have some specific numbers to back up this claim? > > - erik >
Not handy, but I used to build MPI applications on Opterons in 32bit mode, then build them in 64bit mode, and nearly always get a performance boost out of the 64bit. Which was the exact opposite that I'd get on PPC 32 vs 64 bit. PPC's a different animal, using 32bit instructions even when in a "64bit mode" (doesn't really have modes), some immediate memory loads can use up to 5 instructions in assembly... I didn't look much deeper than that. I know I'm not alone in this observation either. I'm sure I could google some results, but I can't currently produce any of my own (unless I can get some time to do so on Leopard, since it supports both). Dave
