[Mpi3-rma] MPI_Fetch_and_op and MPI_Get_accumulate

Hubert Ritzdorf Hubert.Ritzdorf at EMEA.NEC.COM
Wed Nov 28 09:41:41 CST 2012


I have a question:

Is the following combination of accumulate operations allowed and is this the "same operation" ?

Process A and Process B perform a MPI_SUM operation on the same address in the same
window with same predefined datatype but using different RMA function calls:

Process A:

MPI_Get_accumulate (..., target_rank, 0, 1, MPI_LONG_LONG_INT, MPI_SUM, win)

Process B:

MPI_Fetch_and_op(..., MPI_LONG_LONG_INT,  target_rank, 0, MPI_SUM, win)

If the answer is yes, I can't see the advantage of MPI_Fetch_and_op
("might support special hardware operations which use is limited by the generic
functionality of MPI_Get_accumulate")
since these special hardware operations have to be used by all accumulate functions
in the same way (also for very large counts and derived datatypes).

Many thanks in advance

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