Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 19 Mar 2007, Shawn O. Pearce wrote: > > > > DrNick suggested on #git to try flipping the isspace test around. > > This is a smaller change and generated the same ~3.60 seconds run > > as Dscho's patch. I like DrNick's version better. ;-) > > For me, the result seems to be in the noise. > > It may be due to running on Core 2. It's not very sensitive to > micro-optimizations like this. It definitely makes sense to test the > *stable* test first, since that will help branch prediction (the > "isspace()" test is *not* very predictable), so I don't disagree with the > patch, but I suspect it depends a lot on the microarchitecture just how > much it matters. > > Do you perhaps have a P4? It has a very bad branch mispredict penalty, so > putting the predictable branch first could explain the big difference you > see.. I tested both patches on a PowerPC G4. (Apple PowerBook, 1.5 GHz) Running on Mac OS X 10.4.8. Might be more of a Linux<->Darwin thing; perhaps my isspace is significantly slower than yours is... after all my mmap runs like a PC from the 1980s... ;-) -- Shawn. - 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