Speed on P4 Processors

Speed on P4 Processors

We develop a mixed language (VC++ & CVF) application and have begun to notice that execution speed of the compiled app (Fortran part) is slower on P4 than P3 machines. By default we would compile and build on a P3 and deploy common dlls to all users.
Anyone else seen this?

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Just been running a compiled Fortran app that does a lot of matrix math on our new 2GHz P4, 1GB, 400MHz bus machine. It runs about 20% slower than on our 933MHz P3 machine. What gives?

Please let me know if you find a resolution & I'll do the same.

The Pentium 4 is not as good as the Pentium III on a work-per-clock-tick basis, and this is especially true for the "standard" floating point instructions. However, CVF 6.5's code that it generated for Pentium III (/arch:p6p) (the latest it knew) is actually worse than the default due to the Pentium 4's very different memory architecture. Make sure that you are running CVF 6.6 (or 6.6A) and specify /arch:pn4 (or /arch:host). If you set the option "Generate most-optimized code", that will set /arch:host and a few other speed-boosting switches. Also try "maximum optimizations".

I can't promise that your code will now run faster on a Pentium 4 - most do, some don't. Feel free to download the free trial of the Intel Fortran compiler (if you also have Visual C++, which is a prerequisite) and see if it does a better job when you ask it to optimize for the Pentium 4.


Steve - Intel Developer Support

We've installed 6.6a CVF and so far played the tunes with 11 different compiler settings. Interestingly not one of them shows the slightest change in performance. Currently lacking ideas as to what to do next (other than start a full profile, which might take a little time).

Any brighter suggestions?

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