Basic question about MPI

[p***@gmail.com]

Hello,

I have a very basic question about MPI.

I have a computer with 8 processors (each with 8 cores). What is the difference between if I run a program simply by "./program" and "mpirun -np 6 /path/to/program" ? In the first case does the program just use one processor of the 8? If I want the program to use all the 8 processors at the same time, then I have to do with mpirun?

Something fundamental is buggin me. Any explanations will be highly appreciated.

Thank you,
Pradeep

[[e-mail]]

Post by p***@gmail.com
Hello,
I have a very basic question about MPI.
I have a computer with 8 processors (each with 8 cores). What is the difference between if I run a program simply by "./program" and "mpirun -np 6 /path/to/program" ? In the first case does the program just use one processor of the 8? If I want the program to use all the 8 processors at the same time, then I have to do with mpirun?

"./program" just runs the program (i.e., creates one process).

"mpirun -np 6 ...." starts six copies of the program (i.e., creates six
processes). As best I know this is the normal way of starting an MPI
program meant to run on multiple processors.

Post by p***@gmail.com
Something fundamental is buggin me. Any explanations will be highly appreciated.

So I hope you're still checking the group ....

Post by p***@gmail.com
Thank you,
Pradeep