message: Handle timing and synchronization
  Start simply by adding an mpi barrier before starting
  the timer and before stopping the timer. This ensures the ranks
  start in sync and all are done before the final time is taken.
diff: #include "common/RunParams.hpp"
  #include "RAJA/util/Timer.hpp"
  +#if defined(RAJA_PERFSUITE_ENABLE_MPI)
  +#include <mpi.h>
  +#endif
  #if defined(RAJA_ENABLE_CUDA)
  #include "RAJA/policy/cuda/raja_cudaerrchk.hpp"
  #endif
  @@ -118,12 +121,18 @@ public:
  void startTimer()
  {
  synchronize();
  +#ifdef RAJA_PERFSUITE_ENABLE_MPI
  + MPI_Barrier(MPI_COMM_WORLD);
  +#endif
  timer.start();
  }
  void stopTimer()
  {
  synchronize();
  +#ifdef RAJA_PERFSUITE_ENABLE_MPI
  + MPI_Barrier(MPI_COMM_WORLD);
  +#endif
  timer.stop(); recordExecTime();
  }
  