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Old 01-05-03, 12:50 AM   #1
Wonder
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Default Need Gigaflops from GCC on P4

Anybody know how to configure GCC?

I've got SlackWare 8, which for stability reasons has been set up entirely using the '386 instruction set. I think they also have the GCC compiler set up to only generate 386 instructions.

Using this, I can get 0.7 billion double precision floating point operations per second, computing the inner product of two long vectors (on a 1.8GHz Pentium4). That's not bad, but I think I should be able to get more like 8.0 Gflops (10X), if I can invoke the SIMD/SSE2 capabilities of my Pentium 4. The GCC compiler is supposed to support this. I just want to do a little sub-atomic physics at home in my spare time.

I think I may need the -b MACHINE option, which in turn requires (I think?) a library configured for P4 instead of i386. I've tried -mcpu=pentium4 and -march=pentium4 and -msse2 compile options, with no effect. I haven't tried -mfpmath=sse.

Do I need to recompile some libraries for pentium4? Do I need to set up GCC as if it's doing a cross-compile (for a different platform)? Am I even asking the right questions?

Thanks!
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Old 01-16-03, 04:00 PM   #2
ernestus
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Default

Waw, what a level!
I think gnu.org is a good place to start (I think SSE & 3DNOW! are assembly supported, but may be I am wrong).
Luck.
E
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Old 01-16-03, 04:07 PM   #3
ernestus
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Ok, I was wrong, what I said is true in my gcc version. here go two useful links:

here is a discussion about the subject:
http://compilers.iecc.com/comparch/index/2002-05

look for the MMX/3Dnow!/SSE/SSE2 compilers thread. As you can see, SSE2 instructions may take longer than FPU instructions.

And here there is a depiction of what can you expect:
http://www.andrew.cmu.edu/~komarek/w...leskyPerf.html

I realize x86 architecture is not appropiated for number crunching (look at the great results of the humble G3 300MHz Apple iBook)

Bye
E.
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Last edited by ernestus; 01-16-03 at 04:24 PM.
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