• 9.1
  • 08/07/2015
  • Public Content

Ungroup MPI Functions


 Analyze MPI process activity in your application.
To see the particular MPI functions called in the application, right-click on MPI (marked with a red rectangle) in the Event Timeline and select
Ungroup Group MPI
. This operation exposes the individual MPI calls.
After ungrouping the MPI functions, you see that the processes communicate with their direct neighbors using
MPI_Sendrecv
at the start of the iteration.
MPI Ungrouped
This data exchange has a disadvantage: process
i
does not exchange data with its neighbor
i+1
until the exchange between
i-1
and
i
is complete. This delay appears as a staircase pattern resulting with the processes waiting for each other.
The
MPI_Allreduce
at the end of the iteration resynchronizes all processes; that is why this block has the reverse staircase appearance.

Product and Performance Information

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Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.