John Mousel <[email protected]> writes: > I would like to investigate using pipelined GMRES and IBCGS on Kraken but > it seems from the FAQ page that Cray MPT-5.6 is required for the pipelined > methods to be effective. Checking the module avail, I see that they only > have up to MPT-5.3.6. Is there any benefit at all to these methods if I > can't configure with MPT-5.6?
IBCGS does not use pipelining so MPT version is irrelevant. For pipelined GMRES/CG/CR, you need MPT-5.6 or later to use the asynchronous interface (MPI_Iallreduce). Without that, the pipelined methods will do fewer reductions, but they will be synchronous instead of asynchronous, thus likely not paying off. Unfortunately, even MPT-5.6 does not managed to make significant asynchronous progress. So when you use MPI_Iallreduce, almost nothing happens until you call MPI_Wait. The Cray MPI team says they think this is a software/implementation problem rather than a hardware problem, and they are hopeful that they'll be able to release a new MPT that does a good job of making asynchronous progress. This probably means that PGMRES won't provide large benefits until Cray's MPI team writes some code and you switch to a machine that uses that new code.
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