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CS591x Cluster Computing

CS591x Cluster Computing. Interconnect Performance. Interconnect Performance. Major factor in computational performance… For communication intensive applications – collaborative processes Less important for compute intensive/low communications applications.

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CS591x Cluster Computing

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  1. CS591x Cluster Computing Interconnect Performance

  2. Interconnect Performance • Major factor in computational performance… • For communication intensive applications – collaborative processes • Less important for compute intensive/low communications applications

  3. Comparison of Interconnect Technology -estimates

  4. Others • 10 GigE • Coming along • Still expensive • Cray RapidArray Interconnect - XD1 • 9 Gbs bandwidth • 1.8 us latency • Low overhead

  5. Interconnect summary • Fast Ethernet cheap, poor performance • GigE – getting cheaper, better bandwidth, latency and overhead problems • Myrinet, Quadrics – very good bandwidth, low latency, low overhead – expensive – likely to stay expensive

  6. … Interconnect Summary • 10 GigE is coming along – too early to tell • Infiniband is the technology to watch • Very good performance • Expensive, but getting cheaper • Custom “Fabrics” • Very high performance • Cray XD1

  7. Interconnect • Performance influenced by transport protocol (i.e. IP) • Shared memory for communication results in better performance, but may have other problems • Application design may be tuned for particular interconnect architecture

  8. Compiling Programs on energy • C/C++Compilers • gcc/g++ • icc • pgcc/pgCC • mpicc, mpiCC

  9. Compiling Programs on energy • Fortran Compilers • gcc/g77 • Fortran 77 (maybe more coming) • Gcc recognizes file extension (.f, .for,…) • Ifort - Intel Fortran 95 • mpif77 • pgf77 • pgf90

  10. Compiler options • Common options • -o specifies compiler output file • -l specifies libraries that should be linked • -L specifies library paths (important) • -i specifies files to include • -I specifies the path for include files • -i/-I/-l/-L can occur multiple times

  11. Compiler Options • Many compile/link options • Many optimization options (more on this later)

  12. So… • Imagine that you wrote a program called simplehello.c … #include <stdio.h> main() { printf("Hello, World:\n"); }

  13. To compile with gcc • Like this… • gcc simplehello.c –osimplehello • If all goes well, you get a shell prompt (means no errors) • Review compiler errors carefully • Unresolved references usually means something is not defined/can’t find something

  14. Or … • With Intell c/c++ • icc simplehello.c –osimplehello • With mpicc • mpicc simplehello.c –osimplehello • Note: different compilers may have different defaults/definitions

  15. … mpi… • We have to give the compiler more direction … • gcc hello.c –ohellogcc –lmpich –I/usr/local/packages/mpich/include –L/usr/local/packages/mpich/lib • icc hello.c –ohellogcc –lmpich –I/usr/local/packages/mpich/include –L/usr/local/packages/mpich/lib

  16. With mpicc • mpicc hello.c -ohellompi

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