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DMP: Deterministic Shared Memory Multiprocessing

This paper addresses the challenges of non-determinism in current shared memory multicore and multiprocessor systems, which complicates debugging and testing processes. It argues for the advantages of deterministic shared memory multiprocessing, highlighting approaches that focus on inter-thread communication for consistency in output across various program executions. The paper discusses the sources of non-determinism, ranging from software to hardware, and evaluates performance based on different communication strategies. It concludes that implementing deterministic methods can improve scalability and debugging efficacy without significantly hindering performance.

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DMP: Deterministic Shared Memory Multiprocessing

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  1. ECE 259 / CPS 221 Advanced Computer Architecture II DMP: Deterministic Shared Memory Multiprocessing Joseph Devietti et al. Presenter : Tae Jun Ham 2012. 3. 19

  2. Abstract • Most current shared memory multicore and multiprocessor systems are nondeterministic. • Non-determinism makes debugging and testing hard. • Previous approaches were based on replay • But replay is only useful for debugging • Based on deterministic inter-thread communication, this paper suggests several ways to achieve deterministic shared memory multiprocessing

  3. Determinism • What is Deterministic Parallel Execution? • Executes multiple threads that communicate via shared memory • Should produce the same output if given the same program input • What causes Non-determinism? • Software sources : concurrent threads, the state of memory pages, power saving mode, disk and I/O buffer, and some OS system calls. • Hardware sources : state of caches, predictor tables and bus priority controller, and bus arbiters. In other words, almost all microarchitectural structures.

  4. Non-determinism

  5. Non-determinism

  6. DMP-Serial (Fine-Grained)

  7. DMP-Serial (QBcount)

  8. DMP-Serial (Coarse-Grained)

  9. DMP-ShTab • Communication-Free Region: Parallel • Communication : Serial • Rules • Without token: Read for shared address Write for own address • With token: Can do everything

  10. DMP-ShTab

  11. DMP-ShTab

  12. DMP-TM & DMP-TM-Fwd

  13. DMP-TM & DMP-TM-Fwd

  14. DMP-TM & DMP-TM-Fwd

  15. QB-SyncFollow & QB-Sharing QB SyncFollow : After unlock, pass the token QB Sharing : After finishing works on shared data, pass the token

  16. Evaluation - Performance Serial : Linear slowdown with the increasing number of threads ShTab : 38% TM-Fwd : 21%

  17. Evaluation - Quanta size sensitivity In general, larger quanta is slower. Serial case is less sensitive to quanta size.

  18. Evaluation - Heuristics on quanta size Effective for ShTab. SyncFollow benefits for some workloads.

  19. Evaluation - Sw-DMP Author says : In summary, this data shows that Sw-DMP-ShTab does not unduly limit performance scalability for multithreaded applications.

  20. Discussions • Can this system deployed? • Too much performance overhead • Implementation Complexity • Which one do you prefer? DMP vs Deterministic replay • Possible power saving with DVFS?

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