[Caml-list] Using threads for overlapping communication/computation

[Caml-list] Using threads for overlapping communication/computation

[Eray Ozkural]

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Hi there,

Has anybody used OcamlMPI in conjunction with multi-threading to overlap
computation and communication?

During the writing of a parallel information-retrieval code, I have
implemented such a feature spawning a new thread for the communications
routines that correspond to a block of computation. While that proceeds, I
start processing the next block (and I yield the main thread so that some
context switching occurs). I think this would not meet any problems had I
used a single blocking call in the spawned threads. However, this is not the
case. My program performs a quite non-trivial kind of collective
communication: a multi-node accumulation with a complex reduction operator,
and another complex collective communication with output-partitioning.
Naturally, I have to invoke several MPI calls (at least 2*logp presently).
And no matter where I yield, my code slows down compared to the
single-threaded version. I am suspecting this is partially due to the
single-physical-thread feature of the ocaml runtime (and partially due to
stress on the local memory). Do you have any recommendations on handling
such scenarios? It occurred to me that I might be missing a known solution.

Best Regards,

-- 
Eray Ozkural, PhD candidate.  Comp. Sci. Dept., Bilkent University, Ankara
http://groups.yahoo.com/group/ai-philosophy

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