Good points...I'll see if anything can be done to speed up the master. If we can shrink the number of MPI processes without hurting overall throughput maybe I could save enough to fit another run on the freed cores. Thanks for the ideas! I was also worried about contention on the nodes since I'm running multiple MPI processes on the same multi-core box. A typical run is 120 MPI processes on 5 nodes, each with 24 cores. I may play a little with the "--bynode" parameter to see if this has any (significant) effect THANXS amb
-----Original Message----- From: users-boun...@open-mpi.org on behalf of Richard Treumann Sent: Fri 9/24/2010 9:16 AM To: Open MPI Users Subject: Re: [OMPI users] "self scheduled" work & mpi receive??? Amb It sounds like you have more workers than you can keep fed. Workers are finishing up and requesting their next assignment but sit idle because there are so many other idle workers too. Load balance does not really matter if the choke point is the master. The work is being done as fast as the master can hand it out. Consider using fewer workers and seeing if your load balance improves and your total thruput stays the same. If you want to use all the workers you have efficiently, you need to find a way to make the master deliver assignments as fast as workers finish them. Compute processes do not care about fairness. Having half the processes busy 100% of the time and the other half idle vs. having all the processes busy 50% of the time gives the same thruput and the hard workers will not complain. Dick Treumann - MPI Team IBM Systems & Technology Group Dept X2ZA / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601 Tele (845) 433-7846 Fax (845) 433-8363 From: Mikael Lavoie <mikael.lav...@gmail.com> To: Open MPI Users <us...@open-mpi.org> List-Post: users@lists.open-mpi.org Date: 09/23/2010 05:08 PM Subject: Re: [OMPI users] "self scheduled" work & mpi receive??? Sent by: users-boun...@open-mpi.org Hi Ambrose, I'm interested in you work, i have a app to convert for myself and i don't know enough the MPI structure and syntaxe to make it... So if you wanna share your app i'm interested in taking a look at it!! Thanks and have a nice day!! Mikael Lavoie 2010/9/23 Lewis, Ambrose J. <ambrose.j.le...@saic.com> 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? THANXS! amb _______________________________________________ users mailing list us...@open-mpi.org http://www.open-mpi.org/mailman/listinfo.cgi/users _______________________________________________ users mailing list us...@open-mpi.org http://www.open-mpi.org/mailman/listinfo.cgi/users
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