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Open MPI: Binding to core by default

December 18, 2013 at 12:55 pm PST

After years of discussion, the upcoming release of Open MPI 1.7.4 will change how processes are laid out (“mapped”) and bound by default.  Here’s the specifics:

  • If the number of processes is <= 2, processes will be mapped by core
  • If the number of processes is > 2, processes will be mapped by socket
  • Processes will be bound to core
  • MPI_COMM_WORLD ranks will be assigned by slot

These are all the default values — they, of course, can be changed by the user via mpirun CLI options, environment variables, etc.

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EuroMPI’13 Cisco slides: Open MPI Process Affinity User Interface

September 18, 2013 at 5:17 am PST

The slides below are from my presentation at EuroMPI’13 about Open MPI’s flexible process affinity interface (in OMPI 1.7.2 and later).  I described this system in a prior blog entries (one, two, three), but many people keep asking me about it.

Josh Hursey from U. Wisconsin, LaCrosse, wrote this IMUDI paper about the interface (IMUDI is a sub-workshop of EuroMPI focusing on end-user issues) to get a little more publicity and awareness of this process affinity system.  Specifically, we designed this affinity system so that we could get feedback from real end users about what is useful and what is not.

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Open MPI v1.5 processor affinity options

March 9, 2012 at 5:00 am PST

Today we feature a deep-dive guest post from Ralph Castain, Senior Architecture in the Advanced R&D group at Greenplum, an EMC company.

Jeff is lazy this week, so he asked that I provide some notes on the process binding options available in the Open MPI (OMPI) v1.5 release series.

First, though, a caveat. The binding options in the v1.5 series are pretty much the same as in the prior v1.4 series. However, future releases (beginning with the v1.7 series) will have significantly different options providing a broader array of controls. I won’t address those here, but will do so in a later post.

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