Intel® MPI Benchmarks User Guide and Methodology Description

# Synchronization

Before the actual benchmark measurement is performed, several consecutive barrier calls are made to ensure perfect processes synchronization. The `N_BARR` constant defines the number of consecutive calls. The constant is defined in `IMB_settings.h` and `IMB_settings_io.h`, with the current value of 2.

The barrier calls are either ordinary `MPI_Barrier(comm)` calls, or `IMB_barrier(comm)` calls (in the case the `–imb_barrier` option is specified).

See figure Control flow of IMB to understand the way all the processes are synchronized.