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    PDC Presentation Update

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    PDC Presentation Update

    Uploaded by

    mubeen.hasnat76
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    Pdc Presentation Update

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    3 views29 pages

    PDC Presentation Update

    Uploaded by

    mubeen.hasnat76

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 29

    Synchronization Constructs in OpenMP

    Data Handling in OpenMP

    GROUP MEMBERS:
    Haris Mushtaq (21-ARID-576)
    Raja Usama Naveed (21-ARID-659 )
    Zohaib Qaisar Kayani (21-ARID-687 )
    OpenMP: What is it?

    OpenMP is an Application Program Interface (API) for:


    • explicit
    • portable
    • shared-memory parallel programming
    • in C/C++ and Fortran.
    OpenMP consists of:
    • compiler directives,
    • library routines,
    • runtime calls
    • environment variables,
    It is supported by all major compilers on Unix and Windows platforms:
    GNU, IBM, Oracle, Intel, PGI, Absoft, Lahey/Fujitsu, PathScale, HP, MS, Cray
    OpenMP Programming Model

    • Designed for multi-processor/core, shared memory machines.


    • OpenMP programs accomplish parallelism exclusively through
    the use of
    • threads.
    • Programmers has full control over parallelization.
    • Consists of a set of #pragmas (Compiler Instructions/Directives
    that control how the
    • consist of set of programs that control how the program works.
    OpenMP Run Time Variables

    • Modify/check/get info about the number of threads


    omp_get_num_threads() //number of threads in use
    omp_get_thread_num() //tells which thread you are
    omp_get_max_threads() //max threads that can be used

    • Are we in a parallel region?


    omp_in_parallel()
    • How many processors in the system?
    omp_get_num_procs()
    • Explicit locks
    omp_[set unset]_lock()
    And several more...
    I hope this is helpful!
    OpenMP: Few Syntax Details
    • Most of the constructs in OpenMP are compiler directives or
    pragmas
    For C/C++ the pragmas take the form
    #pragma omp construct [clause [clause]...]
    For Fortran, the directives take one of the forms
    C$OMP construct [clause [clause]...]
    !$OMP construct [clause [clause]...]
    *$OMP construct [clause [clause]...]
    • Header File or Fortran 90 module
    #include omp.h
    use omp_lib
    SOME CODE HINTS
    Compiling OpenMP code
    • Same code can run on single-core or multi-core machines.
    • Compiler directives are picked up ONLY when the program is
    instructed to be compiled in OpenMP mode.
    • Method depends on the compiler.
    G++
    $ g++ -o foo foo.c -fopenmp
    ICC
    $ icc -o foo foo.c -fopenmp
    •)

    Running OpenMP code


    • Controlling the number of threads at runtime
    o The default number of threads = number of online processors on the machine
    Environment variables:
    • C shell: setenv OMP_NUM_THREADS number
    • Bash shell: export OMP_NUM_THREADS = number
    • Runtime OpenMP function: omp_set_num_threads(number)
    • Clause in #pragma omp parallel region: num_threads(number)
    Execution Timing:
    #include omp.h
    stime = omp_get_wtime();
    longfunction();
    etime = omp_get_wtime();
    total = etime-stime;
    Thread Creation
    Schedule Clause
    OpenMp for Parallelization
    Sychronization construct
    Synchronization Barriers
    Data Dependencies

    •OpenMP assumes that there is NO data-dependency across jobs


    running in parallel.
    •When the omp parallel directive is placed around a code block,
    it is the
    • programmer's responsibility to make sure data dependency is
    ruled out.
    Synchronization Constructs
    Synchronization Constructs
    OpenMp Data Scoping
    OpenMp private Clause
    OpenMP Parallel Programming
    • Start with a parallelizable algorithm (Loop level parallelism)
    Loop level parallelism
    • Implement Serially: Optimized Serial Program
    • Test, Debug & Time to solution
    • Annotate the code with parallelization and synchronization directives
    • Remove Race Conditions, False Sharing
    • Test and Debug
    • Measure speed-up
    Serial Code:

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