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Subject: Re: [OMPI users] ScaLapack and BLACS on Leopard
From: Michael (mklus_at_[hidden])
Date: 2008-03-06 17:11:13

On Mar 6, 2008, at 12:49 PM, Doug Reeder wrote:
> Greg,
> I would disagree with your statement that the available fortran
> options can't pass a cost-benefit analysis. I have found that for
> scientific programming (e.g., Livermore Fortran Kernels and actual
> PDE solvers) that code produced by the intel compiler runs 25 to 55%
> faster than code from gfortran or g95. Looking at the cost of adding
> processors with g95/gfortran to get the same throughput as with
> ifort you recover the $549 compiler cost real quickly.
> Doug Reeder

I've a big fan of g95, but actually I'm seeing even greater
differences in a small code I'm using for some lengthy calculations.

With 14 MB of data being read into memory and processed:

Intel ifort is 7.7x faster then Linux g95 on MacPro 3.0 GHz
Intel ifort is 2.9x faster then Linux g95 on Dual Opteron 1.4 GHz
Intel ifort is 1.8x faster then Linux g95 on SGI Altix 350 dual
Itanium2 1.4 GHz
OS X g95 is 2.7x faster then Linux g95 on a MacPro 2.66 GHz (same
hardware exactly)

The complete data set is very large, 56 GB, but that is 42 individual
frequencies, where as the 14 MB is a single frequency, data averaged
over areas, so get a favor of the answer but not exactly the right
answer. I played around with compiler options, specified the exact
processor type within the limits of gcc and I gained only factions of
a percent.

A co-worker saw factor 2 differences between Intel's compiler and g95
with a very complicated code.