[mpich-discuss] Single slow mpi process

[Reuti]

Am 26.08.2013 um 12:29 schrieb 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

`mpicc -showme ...` will show the options (and used compiler). Maybe the optimization options are set differently

How fast is the application in case you start the Open MPI compilation without `mpirun` but just execute it in the usual way?

-- Reuti


> 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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