Newsgroups: comp.parallel.mpi
From: eddemain@neumann.uwaterloo.ca (Erik Demaine)
Subject: Re: MPI_SEND is not returning.
Organization: University of Waterloo
Date: Mon, 18 Sep 1995 18:53:17 GMT
Message-ID: <DF474t.85z@undergrad.math.uwaterloo.ca>

Tor Johansen (torj@zapffe.mat-stat.uit.no) wrote:
: I have a program that works fine on an Intel Paragon,
: which I would also like to run on an IBM SP2 - but on
: the SP2 the program does not work fine anymore.
: The program will not return from a call to MPI_SEND.
: Does anybode know what culd be the reason for this? 

It depends on the MPI implementation, but usually the cause of an MPI_Send
blocking is that buffer space is not available, causing a fully blocking
send.  You might want to check if there is sufficient memory on the SP2.

However, you may be making some assumptions about the MPI implementation
which are valid on the Paragon's implementation but not on the SP2.  Most
important, it is possible that MPI_Send does *not* return until the matching
MPI_Recv is completed.  Thus, a processor cannot safely use MPI_Send to
transmit a message to itself.  Be careful of this, and look at the non-blocking
versions of MPI_Send/Recv.

Ciao!
Erik
--
Erik Demaine                 \/  Masters student in Computer Science
Dept. of Computer Science    \/  e-mail: eddemain@neumann.uwaterloo.ca
University of Waterloo       \/  URL   : http://barrow.uwaterloo.ca/~eddemain/
Waterloo, ON Canada N2L 3G1  \/  <<< Space for sale >>>

