Hi All:
I’ve written an openmpi program that “self schedules” the work.
The master task is in a loop chunking up an input stream and handing off
jobs to worker tasks. At first the master gives the next job to the
next highest rank. After all ranks have their first job, the master
waits via an MPI receive call for the next free worker. The master
parses out the rank from the MPI receive and sends the next job to this
node. The jobs aren’t all identical, so they run for slightly different
durations based on the input data.
When I plot a histogram of the number of jobs each worker performed, the
lower mpi ranks are doing much more work than the higher ranks. For
example, in a 120 process run, rank 1 did 32 jobs while rank 119 only
did 2. My guess is that openmpi returns the lowest rank from the MPI
Recv when I’ve got MPI_ANY_SOURCE set and multiple sends have happened
since the last call.
Is there a different Recv call to make that will spread out the data better?
How about using MPI_Irecv? Let the master issue an MPI_Irecv for each
worker and call MPI_Test to get the list of idle workers, then choose
one from the idle list by some randomization?
THANXS!
amb
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