Processes are not spawned by MPI_Init. They are spawned before by some applications between your mpirun call and when your program starts. When it does, you already have all MPI processes (you can check by adding a sleep or something like that), but they are not synchronized and do not know each other. This is what MPI_Init is used for.

Matthieu Brucher

2011/12/14 Dmitry N. Mikushin <maemarcus@gmail.com>

Dear colleagues,

For GPU Winter School powered by Moscow State University cluster
"Lomonosov", the OpenMPI 1.7 was built to test and popularize CUDA
capabilities of MPI. There is one strange warning I cannot understand:
OpenMPI runtime suggests to initialize CUDA prior to MPI_Init. Sorry,
but how could it be? I thought processes are spawned during MPI_Init,
and such context will be created on the very first root process. Why
do we need existing CUDA context before MPI_Init? I think there was no
such error in previous versions.

Thanks,
- D.
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