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difx:difxmpi_mpi_related_issues

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difx:difxmpi_mpi_related_issues [2010/05/23 09:30]
walterbrisken created
difx:difxmpi_mpi_related_issues [2015/10/21 10:08] (current)
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 ==== Message Passing Interface (MPI) Issues ==== ==== Message Passing Interface (MPI) Issues ====
  
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 == OpenMPI == == OpenMPI ==
  
-A vast majority of known DiFX installations use OpenMPI (available at [[:​www.openmpi.org|www.openmpi.org]]). ​ OpenMPI is in active development by many major corporations,​ research institutes, and universities. ​ It rather simply compiles and installs, making use of the GNU configuration tools. ​ OpenMPI makes use of a "​modular component architecture"​ where various subsystems (schedulers,​ transport layer, ...) can each be tuned at run-time for a particular application. ​ Some mpirun options that have been employed by users of DiFX include+A vast majority of known DiFX installations use OpenMPI (available at [[configcode|www.openmpi.org]]). ​ OpenMPI is in active development by many major corporations,​ research institutes, and universities. ​ It rather simply compiles and installs, making use of the GNU configuration tools. ​ OpenMPI makes use of a "​modular component architecture"​ where various subsystems (schedulers,​ transport layer, ...) can each be tuned at run-time for a particular application. ​ Some mpirun options that have been employed by users of DiFX include
  
   * ''​--mca btl ^udapl,​openib'' ​  This option turns off support for Infiniband and hence prevents a warning message from appearing in cases where infiniband is not available. ​ This should be excluded from systems that actually want to use Infiniband.   * ''​--mca btl ^udapl,​openib'' ​  This option turns off support for Infiniband and hence prevents a warning message from appearing in cases where infiniband is not available. ​ This should be excluded from systems that actually want to use Infiniband.
   * ''​--mca mpi_yield_when_idle 1'' ​  This option turns off overly greedy polling of a network socket to reduce CPU usage. ​ For DiFX, latency is not a problem due to the generous buffering at every stage so this should only improve performance.   * ''​--mca mpi_yield_when_idle 1'' ​  This option turns off overly greedy polling of a network socket to reduce CPU usage. ​ For DiFX, latency is not a problem due to the generous buffering at every stage so this should only improve performance.
   * ''​--mca rmaps seq'' ​  This option tells mpirun to assign monotonicly increasing MPI rank strictly according to the ordering of entries in the machines file.  Without this, OpenMPI takes liberties and will change the ordering if the same machine is listed more than once.  This option can be useful if it is necessary to run more than one mpifxcorr process (which itself can have multiple threads) on one machine.   * ''​--mca rmaps seq'' ​  This option tells mpirun to assign monotonicly increasing MPI rank strictly according to the ordering of entries in the machines file.  Without this, OpenMPI takes liberties and will change the ordering if the same machine is listed more than once.  This option can be useful if it is necessary to run more than one mpifxcorr process (which itself can have multiple threads) on one machine.
difx/difxmpi_mpi_related_issues.txt · Last modified: 2015/10/21 10:08 (external edit)