From: Matt Challacombe <mchalla@t12.lanl.gov>
Newsgroups: comp.parallel.mpi
Subject: Nonblocking on shared memory computers
Date: Tue, 15 Jun 1999 11:39:51 -0600
Organization: Theoretical Division, Los Alamos National Lab
Message-Id: <37668FE6.10AAB922@t12.lanl.gov>
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Xref: ukc comp.parallel.mpi:5200


Hi,

I'm trying to develop portable code for irregular scientific
computation on a shared memory computer (SGI's ASCI blue mountain).
To achieve this I am using non-blocking communication and trying to
overlap communication and computation.

The problem I have is that the SGI version of  MPI_ISEND and MPI_IRECV
actually appear to block.  Thus, if I comment out the work that is supposed
to mask communication latency, the communication time actually decreases.

The SGI response is pretty much that non-blocking is not implemented in
hardware,  and I should drop MPI in favor of SHMEM or OpenMP.  It occurs
to me that MPICH must be able to get non-blocking to work without hardware
support, for example on Beowulf type clusters.

I'm wondering if (1) anyone has had similar experiences and found solutions
for SGI shared memory machines (2) if anyone has related non-blocking codes
that run efficiently under MPICH on Beowulfs.  Any references and or
clarification of these matters will be very much appreciated.

Thanks, Matt

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+ Matt Challacombe, Ph.D.           http://www.t12.lanl.gov/~mchalla/ +
+ Los Alamos National Laboratory    email: mchalla@t12.lanl.gov       +
+ Theoretical Division              vmail:   (505) 698-4112           +
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