running Fortran code on Linux

[Christopher Browne]

On 5/10/05, Michael Yang <lr1003-/E1597aS9LQAvxtiuMwx3w at public.gmane.org> wrote:
> I have a CFD Fortran code running on both Windows and Linux platforms. It
> surprised me that on windows system the code can use up to 50% cpu, while it
> can use only about 10% cpu in the linux system even there is no other
> program running. More than 80% of cpu is idle. BTW, both computers have
> intel 3GHz cpu. I am wondering if anyone has experience in programming under
> Linux enviroment. How can I make most use of the system resources, i.e.,
> cpu, memory etc. Does my problem come from the code itself or from other
> things like the compiler etc. 

There's always going to be some bottleneck; it is common for "FORTRANy
applications" to be CPU-bound.

It sounds as though yours might not be CPU-bound, which seems a bit
unusual.  Does the application read/write a lot of data?  If the
program is running in portions that are I/O-heavy, you can expect CPU
load to fall.

Another possibility might be that the system might be swapping, if
your application expects to have way more memory than you really have.

But if that be not the case, what comes to mind as a bottleneck is
memory bandwidth.  Tuning at the compiler level might be relevant
there.

But you need to get a better feel for what is the bottleneck...
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