IntelĀ® MPI Benchmarks User Guide and Methodology Description
Before the actual benchmark measurement is performed, the constant N_BARR is used to regulate calls to:
MPI_Barrier(MPI_COMM_WORLD)
The N_BARR constant is defined in IMB_settings.h and IMB_settings_io.h, with the current value of 2.
See figure Control flow of IMB to ensure that all processes are synchronized.