• 9.1
  • 08/07/2015
  • Public Content

Analyze Optimized Communications


 Investigate other instances of time-consuming MPI calls in the revised application. To do this:
  1. Open the
    Summary Page
    for the
    poisson_icomm.single.stf
    to see the MPI- and CPU-time ratio and get information about the most time-consuming MPI functions. To open the
    Summary Page
    , click the toolbar button.
    You can see that it is the
    MPI_Recv
    function that consumes 5.47% of the MPI time. To take a closer look at the function, click
    Continue
    here and go to the
    Event Timeline
    .
  2. Open the
    Event Timeline
    , zoom into the first bunch of MPI communications and ungroup grouped MPI calls.
  3. Zoom deeper to see the
    MPI_Recv
    calls closer:
    You can see that the processes starting from
    P1
    have already called
    MPI_Recv
    , but are waiting for
    P0
    to send data. This kind of communication generates imbalance which is later reduced by
    MPI_Allreduce
    resynchronizing all the
    MPI_Recv
    calls.
  4. To prove that it is exactly the
    MPI_Recv
    call that causes imbalance, analyze the application with Intel® VTune™ Amplifier XE.
Key Terms

Product and Performance Information

1

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