modified on 30 September 2015 at 06:21 ••• 21,270 views


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Choosing the Right ARMCI Library

The Global Arrays parallel environment relies upon a one-sided communication runtime system. There are at least three options currently available:

  • ARMCI - This is the original one-sided library developed with Global Arrays by PNNL. It supports the widest range of platforms. See for details.
  • ComEx - This library is being developed by PNNL to replace ARMCI. It supports the fewer platforms than ARMCI but may be more robust on modern ones like InfiniBand. See for details.
  • ARMCI-MPI - This library is a completely separate implementation of the ARMCI interface by Argonne and Intel. It uses the one-sided communication features of MPI, rather than a platform-specific conduit. It currents provides both MPI-2 and MPI-3 implementations; the MPI-3 one is supported by nearly all platforms. See for details.

By default, Global Arrays will choose ARMCI or ComEx, based upon the environment variables selected by the user (see GA documentation for details). When a native implementation is available and works reliably, this is the best option for the NWChem user. However, in cases where an native implementation of ARMCI is not available or is not reliable, the user should consider using one of the MPI-based implementations.

There are many different ways to use MPI as the communication runtime of Global Arrays:

ARMCI_NETWORK Additional variables Result
MPI-PR None ARMCI with progress rank
MPI-PT None ARMCI with progress thread
MPI-MT None ARMCI over multi-threaded MPI
MPI-TS None ARMCI over MPI without data server
MPI-SPAWN None ARMCI over MPI using MPI-Spawn to create the extra data server process
ARMCI EXTERNAL_ARMCI_PATH=path-to-armci-mpi ARMCI with progress rank