All, I have been interested in MPI datatypes since reading about them and playing with the benchmark found at http://unixer.de/research/datatypes/ddtbench/ I am working with a weather model that spends considerable time doing halo (aka ghost cell) updates. The existing code uses irecv/isend. Since most of the time spent doing halo updates is actually spent packing and unpacking the MPI buffers, I was hoping the use of datatypes would improve performance. Unfortunately, the datatype version is actually quite a bit slower than the standard non-blocking pt2pt code. I found this to be that case for both mpich-3.1rc1 and a recent version of a vendor MPI implementation (not MPICH based). I have not run this comparison using OpenMPI. Is data type performance an active area of development? Is there room for improvement? Daniel Kokron NASA Ames (ARC-TN) SciCon group 301-286-3959