Try several consecutive runs on 4 PEs. When you run code on multiple processors, each PE gets a copy of the code and then executes that copy. This example shows compiling and running the Hello code on multiple processors. Note that each processor acts independently and sends its output as soon as it is finished with the task. All the examples in Section 2 were malleable.
Malleability is determined at compile time.
Read about the -X option in the man pages for the cc and f90 commands. Compile into different executable files for use later. Run both executables from the command line. Run both executables from mpprun. This useful utility will display summaries of many types of files.