[mpich-discuss] Single slow mpi process

[Reuti]

Ups - sorry. Mixed the two MPI lists I subscribed to... Please ignore this post.


Am 26.08.2013 um 12:43 schrieb 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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>