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Understanding Bulk Synchronous Parallel Computing: A Modern Approach to Algorithm Design

This presentation outlines Bulk Synchronous Parallel (BSP) computing, a paradigm that simplifies the design of scalable software. It introduces the BSP model, emphasizing its importance for tackling the complexities of diverse parallel computing environments. By breaking tasks into manageable supersteps, BSP decouples communication from computation, minimizing deadlock issues and facilitating easier debugging. Real-world applications and basic techniques for implementing BSP highlight its relevance today, making it an essential approach for programmers transitioning from sequential to parallel programming.

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Understanding Bulk Synchronous Parallel Computing: A Modern Approach to Algorithm Design

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  1. Bulk Synchronous Parallel Computing Trevor Schaub Jim Sellers This presentation was prepared for Professor Stefan Dobrev in partial fulfillment of therequirements forthe course CSI 4140

  2. Outline • Model description • Why it is interesting/important • Relationship to real life • Some basic techniques, simple sample program to demonstrate how the approach to algorithm design differs from PRAM and MPP

  3. Why do we need change? • Diverse parallel computers and models • Shared mem. vs. message passing, no clear winner • Use network locality vs. don’t • Conclusion: parallel code is often computer specific. Need unifying model

  4. Why BSP? • Provides consistent, general framework to develop scaleable software • Similar to OO – a way of thinking and writing programs (paradigm) • Not system specific • Proceed in “supersteps” • Decouples communication and synchronization • The deadlock problem is minimized

  5. What is BSP? • BSP is a process of dividing a task into steps called supersteps • Each process performs the task by doing the supersteps in order • The fundamental concept is the superstep itself, and it’s structure

  6. What’s a superstep? • Processes perform as much as possible using local data • Communication and synchronization • Move on to next superstep superstep …

  7. Dissection of a superstep Threads/Processes T I M E Local computation Global Communication Synchronization

  8. Model description • What are the benefits of a superstep? • Easier debugging • Can look at supersteps in isolation • Removes problem of deadlock • Separate computation from communication • Allows reasoning of the correctness of the code nearly as easy as sequential code. • Easier shift for programmers used to sequential programming

  9. Relationship to real life • Is BSP in use today? • Yes, sometimes without even realizing it. • When should you use BSP? • Becomes more useful with more communication • Benefits vary with the problem

  10. Basic techniques • Identify the sections that can be that need communication or synchronization • Modify program so that sync. happens after communication • Separate ones are grouped where possible • Before each communication group there is a global barrier • The code between the end of each communication group becomes a superstep

  11. Example: • See code example

  12. References • http://approximity.com/papers/ptfopt/node31.html • http://www.cs.ucf.edu/csdept/faculty/goudreau/cop5937_fall96/COP5937.html • http://web.comlab.ox.ac.uk/oucl/research/highlights/bsp_computing.html • http://www.math.uu.nl/people/bisselin/pas1_prev.html • http://www.math.ruu.nl/people/bisselin/software.html • http://web.comlab.ox.ac.uk/oucl/work/bill.mccoll/oparl.html • http://www.cs.hmc.edu/courses/2001/spring/cs156/html12/slides12.pdf • http://www.cag.lcs.mit.edu/bayanihan/papers/javapdc99/html/node2.html • http://www.byte.com/art/9611/sec5/art5.htm

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