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pmodels / oshmpi

OpenSHMEM Implementation on MPI
https://pmodels.github.io/oshmpi-www/
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space: add MR_PREFERRED|LAT_PREFERRED hint in space config #118

Closed minsii closed 3 years ago

minsii commented 3 years ago

MPI_PUT|GET may have different internal implementations for latency-preferred or message-rate-preferred program. E.g., if it knows the user program use every MPI_PUT|GET in a blocking manner such as the blocking RMA in SHMEM, then MPI may also want to use a blocking data transfer internally to save some software overhead; if the user program uses MPI_PUT|GET in a nonblocking manner (e.g., issuing multiple shmem_putmem_nbi + single queit), then MPI may want to decouple data transfer and completion check to maximize overlap.

Such a preference can be detected via the use of SHMEM APIs (see above example), but unfortunately is lost when calling MPI RMA. Thus, we have to set a hint at window creation time (i.e., at OSHMPI space creation time).

TODO: also add a similar hint for default windows. May need environment variable.

minsii commented 3 years ago

test:oshmpi/mpich/builtin test:oshmpi/ompi/builtin