[Beowulf] Table of best compiler flags for different CPUs?

Steve Cousins cousins at limpet.umeoce.maine.edu
Tue May 10 11:39:54 PDT 2005

The recent thread comparing Opterons to Xeon/Nocona brought up some
interesting points about compilers for different CPU's.  Has anyone
created a table of CPU type vs Compilers, showing what flags to use to get
the best performance for a given CPU/Compiler pair? 

I know "best performance" depends on the application but hopefully there
are some basic flags that will work pretty well with any floating point
intensive applications (I know, not everyone is doing floating-point
applications but that is my domain). Of primary concern to me are finite
element and finite difference models.  The compilers that I am mainly
interested in are Gnu Fortran, Portland Group Fortran and the Intel
Fortran compilers, although a more complete table would of more general
interest I'm sure.

I have compared a number of CPU's using one of our ocean models and
recently I compared a Dual 3.0 Ghz Xeon Nocona to a Dual 2.6 Ghz Opteron
using an old version (3.2.4) of the Portland Group compiler using the
-fast switch. The Opteron was 71% faster.  This is presumably a fairly
dumb way to test the relative merits of each CPU so (not being a compiler
sophisticate) I am interested in what combinations of compilers and
switches will give a better comparison, as well as run our code faster.



 Steve Cousins, Ocean Modeling Group    Email: cousins at umit.maine.edu
 Marine Sciences, 208 Libby Hall        http://rocky.umeoce.maine.edu
 Univ. of Maine, Orono, ME 04469        Phone: (207) 581-4302

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