[Beowulf] MPI build with different compilers

[Geoff Jacobs]

amjad ali wrote:
> Hi,
> Please reply me about followings:
> 
> 
> 1) Is there any significant performance difference between OpenMPI
> built with GNU compilers and the one built with Intel compilers?

OpenMPI performance is fundamentally limited by communication hardware
and algorithms, so micro benchmarks are going to be fairly invariable
when switching between compilers. I've always been under the impression,
as well, that the performance difference between GCC and ICC was less
than the performance difference between gfortran and IFC. If this is the
case, the fact that OpenMPI is written in C will tend to even things out
further.

Application performance will vary, however, depending on the nature of
the workload. If you stop in at the Church of GIYF, you can find
performance comparisons between several of the Fortran compilers,
including Intel, GFortran, Absoft and Pathscale. As an example,
Polyhedron has a good set of benchmarks available in which gfortran
performs well, beating out Lahey and NAG as well as it's cousin, g95.
http://www.polyhedron.com/pb05-linux-f90bench_AMD0html

For specific elements of the benchmark suite, however, relative
performance between each compiler definitely changes.

> 2) Once we have built mpi on our system and then we remove the C/C++
> and Fortran compilers from the system. Will the mpicc and mpif90 still
> work properly? or the mpi bulit always needs installed base compilers?

MPICC, MPIF90, MPI77 and family are just wrappers which provide the
correct compiler and linker flags for building MPI programs. They really
do nothing which the compiler couldn't do with hand tuned arguments.

-- 
Geoffrey D. Jacobs