[mpich-discuss] Single slow mpi process

[Bob Ilgner]

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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