[Beowulf] wall clock time for mpi_allreduce?
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Charlie Peck charliep at cs.earlham.eduSun Sep 12 05:02:01 PDT 2010
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On Sep 10, 2010, at 10:46 PM, xingqiu yuan wrote: > Hi > > I found that use of mpi_allreduce to calculate the global maximum and > minimum takes very long time, any better alternatives to calculate the > global maximum/minimum values? If only the rank 0 process needs to know the global max and min you can use MPI_Reduce() rather than MPI_Reduceall() which will substantially reduce the communication time. The difference is that with MPI_Reduce() the result of the reduction is not communicated back to the other ranks. charlie
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