RS: [Beowulf] Sempron compile optimization

[Alan Ward]

I'm running a Fedora, classicaly compiled for "i686", on the aforesaid Semperon 3000+ (actually a 1800MHz clock).

>Sorry, to be more explicit, I think that MOST people probably don't want
>to use -m features, whether or not they work.  The compiler will usually
>"do the right thing" without them, unless you are cross-compiling.  I
>think they are there mostly for cross-compilers.

So far, a quick series summation gave me:

* "vanilla" gcc (no switches):  19.1 s

* add -march=athlon: 9.9 s

* other FPU options (-sse, -3dnow) have no further effect, probably incorporated into athlon.

* replace with -march=x86-64: 8.3 s

* add -m64: cc1 complains, doesn't compile. Doc says it should work (yah).

No exactly rocket science, but a 130% speedup that doesn't cost anything. Disclaimer: probably depends quite a lot on your code, as usual.

The bad news is: you also get to recompile all your dynamically linked libraries, or you don't win anything. Happened to me with libgmp.

Best,
Alan Ward



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