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  1. Parallel Computing @ ISDS Chris Hans 29 November 2004

  2. Organization • Basics of Parallel Computing • Structural • Computational • Coding for Distributed Computing • Examples • Resources at Duke • CSEM Cluster Parallel Computing @ ISDS

  3. Basics of Distributed Computing • Online Tutorial (Livermore Nat. Lab.) http://www.llnl.gov/computing/tutorials/parallel_comp/ • Serial Computing: one computer, one CPU • Parallel Computing: multiple computers working at the same time Parallel Computing @ ISDS

  4. Various Setups • Collection of Workstations • PVM (Parallel Virtual Machine) • R (rpvm, Rmpi, SNOW) • LAM-MPI (Local Area Multicomputer) • Matlab • Dedicated Cluster • Master/Slave model • MPI Parallel Computing @ ISDS

  5. Network Layout • Basic layout: Each node has: CPU(s), memory Parallel Computing @ ISDS

  6. Designing a Parallel Program Do the nodes need to interact? • “Embarrassingly Parallel” Very little communication -- Monte Carlo • “Shamelessly Parallel” Communication Needed -- Heat diffusion models -- Spatial models Parallel Computing @ ISDS

  7. Message Passing Interface • “MPI” Standard Easy to use functions that manage the communication between nodes. Parallel Computing @ ISDS

  8. Master/Slave Model • Organize the layout: Slaves Parallel Computing @ ISDS

  9. Master/Slave Model • “Master” divides the task into pieces… • …while slaves “listen” to the network, waiting for work. • Master sends out the work to be done… • …slaves do the work… • …while the Master waits for the answers. • Slaves return the results. Parallel Computing @ ISDS

  10. Example: Monte Carlo Parallel Computing @ ISDS

  11. Example: Monte Carlo Parallel Computing @ ISDS

  12. Code • Write ONE program • Same for master and slaves • Run program on EACH node • Each program has to figure out if it’s the master or a slave • MPI Parallel Computing @ ISDS

  13. Master Slave 1 Slave 2 Slave 3 LOAD DATA; GET ID; IF(ID==MASTER) { MASTER(); } ELSE { SLAVE(); } ... LOAD DATA; GET ID; IF(ID==MASTER) { MASTER(); } ELSE { SLAVE(); } ... LOAD DATA; GET ID; IF(ID==MASTER) { MASTER(); } ELSE { SLAVE(); } ... LOAD DATA; GET ID; IF(ID==MASTER) { MASTER(); } ELSE { SLAVE(); } ... Pseudo Code Parallel Computing @ ISDS

  14. Master Slave 1 Slave 2 Slave 3 MASTER { // Find # of nodes GET NP; for(i in 1:NP) { “Tell process i to compute the mean for 1000 samples” } RET=RES=0; // Wait for results WHILE(RET<NP){ ANS = RECEIVE(); RES+=ANS/NP; RET++; } SLAVE { ANS = 0; // Wait for orders // Receive NREPS for(i in 1:NREPS) { ANS += DRAW(); } SEND(ANS/NREPS); RETURN TO MAIN; }; SLAVE { ANS = 0; // Wait for orders // Receive NREPS for(i in 1:NREPS) { ANS += DRAW(); } SEND(ANS/NREPS); RETURN TO MAIN; }; SLAVE { ANS = 0; // Wait for orders // Receive NREPS for(i in 1:NREPS) { ANS += DRAW(); } SEND(ANS/NREPS); RETURN TO MAIN }; Parallel Computing @ ISDS

  15. Master Slave 1 Slave 2 Slave 3 PRINT RES; RETURN TO MAIN; } ... FINALIZE(); } ... FINALIZE(); } ... FINALIZE(); } ... FINALIZE(); } Pseudo Code Parallel Computing @ ISDS

  16. Example: C++ Code • Large dataset • N=40, p = 1,000 • One outcome variable, y • Calculate R2 for all 1-var regression • parallel_R2.cpp Parallel Computing @ ISDS

  17. CSEM Cluster @ Duke • Computational Science, Engineering and Medicine Cluster http://www.csem.duke.edu/Cluster/clustermain.htm • Shared machines • Core Nodes • Contributed Nodes Parallel Computing @ ISDS

  18. CSEM Cluster Details • 4 Dual processing head nodes • 64 Dual processing shared nodes • Intel Xeon 2.8 GHz • 40 Dual processing “stat” nodes • Intel Xeon 3.1 GHz • 161 Dual processing “other” nodes • Owners get priority Parallel Computing @ ISDS

  19. Parallel Computing @ ISDS

  20. Using the Cluster • Access limited • ssh –l cmh27 cluster1.csem.duke.edu • Data stored locally on cluster • Compile using mpicc , mpif77, mpif90 • Cluster uses SGE Queuing System Parallel Computing @ ISDS

  21. Queuing System • Submit your job with requests • memory usage • number of CPUs (nodes) • Assigns nodes and schedules job • Least-loaded machines fitting requirements • Jobs run outside of SGE are killed Parallel Computing @ ISDS

  22. Compiling Linked libraries, etc… g++ -c parallel_R2.cpp -I/opt/mpich-1.2.5/include -L/opt/mpich-1.2.5/lib mpicc parallel_R2.o -o parallel_R2.exe -lstdc++ -lg2c -lm Parallel Computing @ ISDS

  23. Submitting a Job • Create a queue script: Email me when the job is submitted and when it finishes #!/bin/tcsh # #$ -S /bin/tcsh -cwd #$ -M username@stat.duke.edu -m b #$ -M username@stat.duke.edu -m e #$ -o parallel_R2.out -j y #$ -pe low-all 5 cd /home/stat/username/ mpirun -np $NSLOTS -machinefile $TMPDIR/machines parallel_R2.exe Output file Priority and number of nodes requested Your Home Directory on CSEM Cluster Parallel Computing @ ISDS

  24. Submitting a Job • Type: [cmh27@head1 cmh27]$ qsub parallel_R2.q Your job 93734 ("parallel_R2.q") has been submitted. • Monitoring http://clustermon.csem.duke.edu/ganglia/ Parallel Computing @ ISDS

  25. Downloadable Files You can download the slides, example C++ code and queuing script at: http://www.isds.duke.edu/~hans/tutorials.html Parallel Computing @ ISDS