Is there any difference between I_MPI_HYDRA_ENV=all and mpirun -genvall?

[JSCHO]

Hi.

Perhaps this is a stupid beginner’s question, but anyway: I know that I_MPI_HYDRA_ENV=all is the default. Does this imply “mpirun -genvall”? Or is there any difference between these approaches of defining and passing configuration settings for the IMPI?

Or in other words: If I need to define settings like, e.g., I_MPI_HYDRA_BOOTSTRAP and I_MPI_CBWR, will it be sufficient to define these settings as environment variables, or will I also have to add arguments to the mpirun command like -genvall or -genv I_MPI_CBWR=x?

Thanks in advance for an explanation.
Jan

[TobiasK · Accepted solution]

@JSCHO no you don't need to use -genv I_MPI_CBWR or -genvall

[JSCHO]

Thanks for your reply. That's what I suspected.
Just out of curiosity: Since defining I_MPI_* environment variables is sufficient, what is the purpose of the mpirun option "-genv*"?

[TobiasK]

Mainly for MPMD launch scenarios:

https://www.intel.com/content/www/us/en/docs/mpi-library/developer-guide-linux/2021-13/mpmd-launch-mode.html

[JSCHO]

Thank you for the explanation.