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NGS computation services: APIs and Parallel Jobs

NGS computation services: APIs and Parallel Jobs. Richard Hopkins rph@nesc.ac.uk NGS Induction – Rutherford Appleton Laboratory, 2 nd / 3 rd November 2005. Overview. The C and Java API’s to the low-level tools Using multiple processors. Job submission so far. Command-line interfaces.

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NGS computation services: APIs and Parallel Jobs

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  1. NGS computation services: APIs and Parallel Jobs Richard Hopkinsrph@nesc.ac.uk NGS Induction – Rutherford Appleton Laboratory, 2nd / 3rd November 2005

  2. Overview • The C and Java API’s to the low-level tools • Using multiple processors NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  3. Job submission so far Command-line interfaces GLOBUS, etc. GLOBUS, etc. User’s Interface to the grid NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  4. Application-specific tools Application Specificand / or Higher generic tools e.g. BRIDGES Command-line interfaces GLOBUS, etc. User’s Interface to the grid NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  5. Application-specific tools • API’s: • Java • C • … Application Specificand / or Higher generic tools e.g. BRIDGES Command-line interfaces GLOBUS, etc. User’s Interface to the grid NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  6. Available API’s • C http://www.globus.org/developer/api-reference.html • “Community Grid” CoG http://www.cogkit.org/ • Java, Python, Matlab • (very limited functionality on Windows – no GSI) NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  7. Non-communicating Processes Globus_job_submit UI Internet Head processors of clusters Worker processors of clusters Processes run without any communication between them NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  8. Communicating Processes Globus_job_submit UI Internet Head processors of clusters Worker processors of clusters Processes send messages to each other – Must run on same cluster NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  9. Communicating Processes UI Internet Head processors of clusters MPI Worker processors of clusters Processes send messages to each other – Must run on same cluster NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  10. Modes of Parallelism • Communicating processes: on NGS, you run one globus-job-submit command – but need to code and build program so it is parallelised - MPI • Communicating processes: on NGS, multiple executables run from a script on the UI The NGS nodes open these routes to you – but you have to do a bit of work! (Grid is not magic!...) NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  11. MPI notes • How could the task be split into sub-tasks? • By functions that could run in parallel??! • By sending different subsets of data to different processes? More usual ! Overheads of scatter and gather • Need to design and code carefully: be alert to • sequential parts of your program (if half your runtime is sequential, speedup will never be more than 2) • how load can be balanced (64 processes with 65 tasks will achieve no speedup over 33 processes) • Deadlock! • MPI functions are usually invoked from C, Fortran programs, but also Java • Several example patterns are given in the practical.Many MPI tutorials are on the Web! NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

  12. Practical • C API Example • Java API usage • Concurrent processing • MPI example • Follow link from http://homepages.nesc.ac.uk/~gcw/NGS/ NGS Induction, RAL 2nd/3rd Nov 2005 – Computation Services – Richard Hopkins

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