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When are control messages handled?

Learn about different methods used to handle control messages in MPI, including polling, interrupts, and during MPI calls or periodic "polls". Understand the pros and cons of each method and their impact on performance.

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When are control messages handled?

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  1. When are control messages handled? • Polling • During MPI calls or periodic “polls” • Interrupts • When message arrives at process (e.g., OS signals an I/O event) • No method is “best”

  2. MPI_Send User System Sync Delay Transfer Request Acknowledgment System User Polling Mode MPI

  3. MPI_Send User System Transfer Acknowledgment Request System User Interrupt Mode MPI • Cost of interrupt higher than polling (usually)

  4. Example of the effect of Polling • IBM SP2 MPI_Allreduce times for each mode • Times in usecs. Similar effects on other operations. • BUT some programs (with extensive computing) can show better performance with interrupt mode

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