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[bug #38092] Optionally support distributed memory machines using MPI

From: anonymous
Subject: [bug #38092] Optionally support distributed memory machines using MPI
Date: Wed, 16 Jan 2013 15:15:08 +0000
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:11.0) Gecko/20100101 Firefox/11.0

Follow-up Comment #8, bug #38092 (project findutils):

> TOT_RANKS=# some decimal value
> ARGS_PER_RANK=# another decimal value
> xargs --process_slot_var=RANK -P $TOT_RANKS -n $ARGS_PER_RANK
> sh -c 'mpirun -n $RANK yourcommand "$@"' dollarzero

The above doesn't work in practice because an MPI parallel program has to be
started by mpirun or equivalent (at least in all systems that I've used [Cray
XT4&5, IBM Blue Gene P, etc.]). Furthermore since the environment given to
each copy of a program started by MPI is still identical xargs cannot know
which files a particular instance should process without calling
MPI_Comm_rank(...). At least I don't see how else that could be accomplished
portably and reliably (i.e. without looking at node hostnames or such, which
might not even exist).

I cannot test the above commands but I suspect they also wouldn't work because
the -n given to mpirun specifies the total number of processes to start, not a
quantity going from 0 to n - 1.


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