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Measuring Communication and Computation Overlap
Measuring Pure Communication Time
Iallgather
Iallgather_pure
Iallgatherv
Iallgatherv_pure
Iallreduce
Iallreduce_pure
Ialltoall
Ialltoall_pure
Ialltoallv
Ialltoallv_pure
Ibarrier
Ibarrier_pure
Ibcast
Ibcast_pure
Igather
Igather_pure
Igatherv
Igatherv_pure
Ireduce
Ireduce_pure
Ireduce_scatter
Ireduce_scatter_pure
Iscatter
Iscatter_pure
Iscatterv
Iscatterv_pure
Synchronization
Before the actual benchmark measurement is performed, several consecutive barrier calls are made to ensure perfect processes synchronization. The N_BARR constant defines the number of consecutive calls. The constant is defined in IMB_settings.h and IMB_settings_io.h, with the current value of 2.
The barrier calls are either ordinary MPI_Barrier(comm) calls, or IMB_barrier(comm) calls (in case the –imb_barrier option is specified).
See figure Control flow of IMB to understand the way all the processes are synchronized.