[mpich-discuss] Single slow mpi process

[Pavan Balaji]

This is very surprising.  We try to keep the mpicc compile mode as 
similar to the native compiler as possible.

What's the output of:

% mpicc -show

Are the compile flags very different?

  -- Pavan

On 08/26/2013 05:29 AM, Bob Ilgner wrote:
> Dear all,
> When adding #include "mpi.h" and building a single process with mpi, I
> find that the single process mpi job runs very much slower than a single
> thread process built with gcc. i.e. 150 to 200% slower, and run as a
> standalone executable.
> That is, for example
> gcc mycode.c -o mycode.exe
> ./mycode
> will run in 100 seconds.
> Adding #include "mpi.h" to mycode.c
> mpicc mycode.c -o mycode.exe
> mpirun -n 1 mycode.exe
> will take 180 to 400 seconds to run.
> This varies from system to system on intel, Sparc or IBM based systems.
> Can anyone explain this offhand ? Has anyone else experienced this ?
>
>
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-- 
Pavan Balaji
http://www.mcs.anl.gov/~balaji