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Understanding MPI: Clean Messaging and Packet Reassembly

The Message Passing Interface (MPI) is essential for developing message-passing programs with its clean and powerful interface. This library provides standard primitives like MPI_Init, MPI_Comm_rank, and MPI_Send/Recv for effective communication. Using General Dynamic Network (GDN), messages must be packetized, enabling reassembly of logical MPI messages from raw data. The example illustrates how a tile can receive and process packets in a specified order, demonstrating the initial state, packet addition, and buffer management. Get equipped with MPI for streamlined multi-process communication.

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Understanding MPI: Clean Messaging and Packet Reassembly

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  1. rMPIA Message Passing Library for Raw James Psota

  2. What is MPI? • Clean and powerful interface for writing message passing programs • A set of well-defined standard primitives with which many programmers are familiar James Psota

  3. Six Function MPI • MPI_Init: initializes MPI system • MPI_Comm_rank: returns “id” of calling tile • MPI_Comm_size: returns number of tiles running MPI program • MPI_Send: blocking send • MPI_Recv: blocking receive • MPI_Finalize: cleans all MPI state James Psota

  4. Packets • Use General Dynamic Network (GDN) • Must “packetize” MPI messages (GDN supports ≤ 31 words per Raw message) • Receiver must be able to re-assemble packets into logical MPI messages James Psota

  5. Packet Structure • First packet • Later packet James Psota

  6. Re-assembling Packets Example: tile02 does a MPI_Recv(src=0, tag=7), but also receives packets from other sources as well, in the in the following order: (note: <src,tag>) <6,1>, <0,2>, <0,7>, <6,1>, <0,7>, <6,1>, <0,7>, <0,7>, <0,7> James Psota

  7. Initial State: empty James Psota

  8. Add <6,1>1 James Psota

  9. Add <0,2>1 James Psota

  10. Add <0,7>1 James Psota

  11. Add <6,1>2 James Psota

  12. Add <0,7>2 James Psota

  13. Add <6,1>3 James Psota

  14. Add <0,7>3 James Psota

  15. Add <0,7>4 James Psota

  16. Add <0,7>5 James Psota

  17. Copy Into Tile02’s Buffer James Psota

  18. Clean-up State James Psota

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