Measure MPI Load Imbalance

using PAT_RT_MPI_SYNC to measure time at barrier

Environment variable: PAT_RT_MPI_SYNC

In MPI programs, time spent waiting at a barrier before entering a collective can be a significant indication of load imbalance. The PAT_RT_MPI_SYNC environment variable, if set, causes the trace wrapper for each collective subroutine to measure the time spent waiting at the barrier call before entering the collective. This time is reported by pat_report in the function group MPI_SYNC, which is separate from the MPI function group, which shows the time actually spent in the collective.

This environment variable affects tracing experiments only and is set on by default.