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MPI One-Sided and Two-Sided Communication

MPI One Sided and Two-Sided Communication: Table of Contents. MPI CommunicationIntroduction to MPI CommunicationExample of MPI CommunicationMPI Two-Sided Communication Definition of MPI Two-Sided CommunicationExample of MPI Two-Sided CommunicationDiagram of MPI Two-Sided CommunicationMPI One-

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MPI One-Sided and Two-Sided Communication

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    1. MPI One-Sided and Two-Sided Communication Computer Science Colloquium Akinwunmi (Akin) Odeniyi Advisor: Dr. Kai Wang, PhD.

    2. MPI One Sided and Two-Sided Communication: Table of Contents MPI Communication Introduction to MPI Communication Example of MPI Communication MPI Two-Sided Communication Definition of MPI Two-Sided Communication Example of MPI Two-Sided Communication Diagram of MPI Two-Sided Communication MPI One-Sided Communication. Definition of MPI One-Sided Communication Example of MPI One-Sided Communication Diagrams of MPI One-Sided Communication 5/18/2012 2

    3. MPI One Sided and Two-Sided Communication: Table of Contents Transposing an n by n matrix using two processors Program code using Two-Sided Communication Program code using One-Side Communication Performance study of MPI communication models Tabulation of data Graphs of findings Analysis of results Conclusion. Review. Sources. Thanks 5/18/2012 3

    4. MPI Communication: Introduction MPI (Message Passing Interface) is a Library specification for message passing. Standard for writing message-passing programs. It allows many computers to communicate . There are two types of MPI Communication MPI Two-Sided Communication Model MPI Standard 1 (MPI-1). MPI One-Sided Communication Model MPI Standard 2 (MPI-2). 5/18/2012 4

    5. MPI Communication: Why is Communication Needed? Assume we want to add numbers 1 to 100. Let a processor perform an addition in 1 second. This processor will sum all numbers in 99 seconds. Two processors can reduce computation time. Each processor will sum numbers in 49 seconds. It requires 1 second to add the two final results. Processors need to communicate in order to: Distribute the numbers 1 to 100 evenly. Determine the sum of their computation results. Communication is needed in MPI for effective programming. 5/18/2012 5

    6. Two-Sided Communication in MPI-1: Definition Two-Sided Communication Evident in the use of most MPI function calls. Parameters is specified by sender and receiver. Data moves between processes address spaces. Senders Side: MPI_Send() function is called. Receivers Side: MPI_Recv() function is used. Implies some degree of synchronization Receive cant complete until send has started. 5/18/2012 6

    7. MPI Two-Sided Communication: Example The sum of 1 to 100 described above can be done with Two-Sided communication model. Processor 1 Sends the numbers {1, 3, , 99} to processor 2. Receives the sum of {1, 3, , 99} from processor 2. Processor 2 Receives sequence {1, 3, , 99} from processor 1. Sends the series: 1 + 3 + + 99 to processor 1. 5/18/2012 7

    8. Two-Sided Communication: Diagram 5/18/2012 8

    9. One-Sided Communication in MPI-2: Definition Remote Memory Access (RMA) One process specifies communication parameters. Separates communication and synchronization. User imposes right ordering of memory accesses. Origin: the process that performs the call. Target: the process in which memory is accessed. Communication calls MPI_Get: Remote read. MPI_Put: Remote write. 5/18/2012 9

    10. MPI One-Sided Communication: Example. Given a sequence {1, , n} and 2 processors. Processor 1 Loops through {1, , n}. It Informs processor 2 each time it finds a prime. Does not know when next prime will be found. Uses MPI_Put to notify processor 2 of primes. Processor 2 need not loop through {1, , n}. It Does not know how many primes will be found. Remains idle till processor 1 finds or sends prime. 5/18/2012 10

    11. One-Sided Communication: MPI_Get 5/18/2012 11

    12. One-Sided Communication: MPI_Put 5/18/2012 12

    13. One -Sided and Two-Sided Communication: Transposing a Matrix Transposing an n x n matrix named M. For all integer i in [1, n] For all integer j in [1, n] Mji = Mij Programs were written in c language. Programs ran on 2 processors in the rio machine. matTran2.c used MPI_Send and MPI_Recv. matTran1.c used the MPI_Get function. Duration of transposition is given in seconds. 5/18/2012 13

    14. Transposing a Matrix with Two-Sided Communication: matTran2.c t1 = MPI_Wtime(); for(i=0; i<numRows; i++){ for(j=0; j<numCols; j++){ if(myid==0){ matrixVal = matrixArray[k]; k++; MPI_Send(&matrixVal, 1, MPI_INT, 1, tag, MPI_COMM_WORLD); } if(myid==1) { MPI_Recv(&matrixVal, 1, MPI_INT, 0, tag, MPI_COMM_WORLD, &status); matrixArray[(numRows*j)+i] = matrixVal; } } } t2 = MPI_Wtime(); 5/18/2012 14

    15. Transposing a Matrix with One-Sided Communication: matTran1.c if(myid==0){ t1 = MPI_Wtime(); t2 = MPI_Wtime(); t3 = t2-t1; } t1 = MPI_Wtime(); if(myid==0) MPI_Win_create(&matrixVal, sizeof(int), sizeof(int),MPI_INFO_NULL, MPI_COMM_WORLD, &win); else MPI_Win_create(NULL, 0, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win); for(i=0; i<numRows; i++) { for(j=0; j<numCols; j++) { 5/18/2012 15

    16. Transposing a Matrix with One-Sided Communication: matTran1.c if(myid==0){ matrixVal = matrixArray[k]; k++; MPI_Win_fence(0, win); MPI_Win_fence(0, win);} if(myid==1) { MPI_Win_fence(0, win); MPI_Get(&matrixVal, 1, MPI_INT, 0, 0, 1, MPI_INT, win); MPI_Win_fence(0, win); matrixArray[(numRows*j)+i] = matrixVal;} } } //ends for loops MPI_Win_free(&win); t2 = MPI_Wtime(); duration = t2-t1-t3; 5/18/2012 16

    17. Performance of One-Sided and Two-Sided Communication: Table 5/18/2012 17

    18. Performance of One-Sided and Two-Sided Communication: Graph 1 5/18/2012 18

    19. Performance of One-Sided and Two-Sided Communication: Graph 2 5/18/2012 19

    20. Performance of One-Sided and Two-Sided Communication: Analysis MPI 2-Sided functions transposed the n by n matrix in lesser time for all n observed. Time measured for MPI_Get 1-Sided function increased at a faster rate as n increased. matTran2 halted for n >= 512 with an out of resources error, but matTran1 ran for n > 512. Elapsed time for n = 1 was greater than that for n = 2 in both communication models. 5/18/2012 20

    21. MPI One-Sided and Two-Sided Communication: Summary For efficiency purposes, MPI Two-Sided communication model is better and faster. Every Two-Sided communication problem can be solved with One-Sided communication. Moreover, some problems cannot be solved by MPI Two-Sided communication model. Only MPI One-Sided model will work for the prime number example mentioned earlier. 5/18/2012 21

    22. MPI One-Sided and Two-Sided Communication: Future MPI_Probe() in MPI Standard 1: Solves One-Sided Communication problems. Allows incoming message to be checked for. Does not receive incoming messages. Future research: Comparing performance of the two models. Solving a one sided communication problem. Using MPI_Send, MPI_Recv, and MPI_Probe. Using MPI_Get and or MPI_Put. 5/18/2012 22

    23. MPI One-Sided and Two-Sided Communication: Sources MPICH Home Page: http://www.mcs.anl.gov/research/projects/mpi/mpich1/ MPICH2: High-performance and widely portable MPI http://www.mcs.anl.gov/research/projects/mpich2/ High Performance Computing Class Notes: http://www.usd.edu/~Kai.Wang/Teach.html 5/18/2012 23

    24. MPI One-Sided and Two-Sided Communication: Appreciation Thanks to computer science faculty and staff. Thank you for your time and attention. Gratitude goes to friends and family. Glory be to God! Questions? 5/18/2012 24

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