1. PADS 20021 Conservative Simulation using Distributed-Shared Memory Teo, Y. M., Ng, Y. K. and Onggo, B. S. S. Department of Computer Science National University of Singapore

2. PADS 20022 Improve performance of SPaDES/Java by reducing overhead:  Synchronization of events  Distributed communications Study the memory requirements in parallel simulations. Objectives

3. PADS 20023 Presentation Outline Parallel Simulation Null Message Protocol Performance Improvement Memory Requirement Conclusion

4. PADS 20024 Parallel Simulation Sequential simulations execute on a single thread in one processor. Ideally, parallelizing the simulation should enhance its real-time performance since the workload is distributed. The need to maintain causality throughout a parallel simulation => Event synchronization protocols. => Adds to inter-process communications. => New bottleneck!

5. PADS 20025 Null Message Protocol First designed by Chandy and Misra (1979). Prevents deadlock situations between LPs. LP i sends null messages to each of its neighbours at the end of every simulation pass, with timestamp = local virtual time of LP i. Timestamp on null message, T, indicates that the source LP will not send any messages to other LPs before T.

6. PADS 20026 LP 4 4 4 4 Null Message Protocol Clock = 4 LP FEL 4 7 LP

7. PADS 20027 Chandy-Misra-Byrant’s (CMB) protocol performs poorly due to high null message overhead. It transmits null msgs on every simulation pass NMR ~> 1 for nearly all [0, T). Optimizations incorporated:  Carrier-null message scheme  Flushing mechanism  Demand-driven null message algorithm  Remote communications using JavaSpace Performance Improvement

8. PADS 20028 Carrier-Null Message Algorithm Problem with cyclic topologies Use carrier-null message algorithm (Wood, Turner, 1996) Avoids transmissions of redundant null messages in such cycles.

9. PADS 20029 Output Channel (A) 252035 REQ 30 Request Channel (B) Logical Process (A) Logical Process (B) FEL 20 18 35 Flusher Performance Improvement Demand driven null messaging + flushing

10. PADS 200210 Experiments conducted using PC cluster of 8 nodes running RedHat Linux version 7.0. Each node is a Pentium II 400 MHz processor with 256 MB of memory connected through 100 Mbps switch. 2 benchmark programs  PHOLD system  Linear Pipeline Performance Evaluation

11. PADS 200211 PHOLD (3x3, m) Node Closed system

12. PADS 200212 Linear Pipeline (4,  ) Open system Service Center Service Center Service Center Service Center Customer population Depart

13. PADS 200213 PHOLD (n x n, m) CMB + Carrier-Null + Flushing + Demand-driven null msging

14. PADS 200214 Linear Pipeline (n,  ) CMB + Carrier-Null + Flushing + Demand-driven null msging

15. PADS 200215 %tage Reduction in NMR:  PHOLD system CMB  Carrier-null  30%  Flushing incorporated  42%  Demand-driven null msg  55%  Linear Pipeline CMB  Carrier-null  0%  Flushing incorporated  23%  Demand-driven null msg  35% Performance Summary

16. PADS 200216 Distributed Communications Originally, SPaDES/Java uses the RMI library to transmit messages between remote LPs. But the serialization phase presents a bottleneck. Previous performance optimization effort: message deflation. Only solution to overcome remote communications overhead => send less messages. How? Target at null messages.

17. PADS 200217 JavaSpaces A special Java-Jini service developed by Sun Microsystems, Inc., built on top of Java’s RMI, mimicking a tuple space. Abstract platform for developing complex distributed applications. Distributed data persistence. Holds objects, known as entries, with variable attribute types. Key concept: matching of attribute types/values.

18. PADS 200218 JavaSpaces Client write Notifier notify read take  4 generic operations: write, read, take and notify.

19. PADS 200219 Replace the RMI communication module in SPaDES/Java with one running on a single JavaSpace. Use a FrontEndSpace: permits crash recovery of entries in the space. Transmission of processes and null messages between remote hosts go through theFrontEndSpace as space entries. Distributed Communications

20. PADS 200220 LP1LP2 Space Communications : Processes Time = 0 Time = t > 0 SProcess receiver = 1 SProcess sender = 2 receiver = 1 …….. SProcess receiver = 2

21. PADS 200221 LP1LP2 Space Communications : Null Messages NullMsg sender = 2 …….. Req sender = 2 LP3 LP4 Req sender = 2

22. PADS 200222 Performance Evaluation – PHOLD(n x n, m) RMI JavaSpace (4 procs) JavaSpace (8 procs)

23. PADS 200223 Overall Performance Evaluation – PHOLD(n x n, m) CMB + Carrier-Null + Flushing + Demand-driven null msging JavaSpace (4 procs) JavaSpace (8 procs)

24. PADS 200224 %tage Reduction in NMR: CMB  Carrier-null  30%  Flushing incorporated  42%  Demand-driven null msg  55%  JavaSpace (4 processors)  63%  JavaSpace (8 processors)  74% Performance Summary

25. PADS 200225 M prob  n i=1 MaxQueueSize(LP i ) M ord  n i=1 MaxFELSize(LP i ) M sync  n i=1 MaxNullMsgBufferSize(LP i ) Memory Requirement

26. PADS 200226 Memory Requirement

27. PADS 200227 Achievements & Conclusion Enhanced the performance of SPaDES/Java through various synchronization protocols, achieving an excellent NMR of < 30%. Implemented a brand new discrete-event simulation library based on the concept of shared memory in a JavaSpace. Implemented a TSA into SPaDES/Java that can be used as a bench for memory usage studies in parallel simulations.

28. PADS 200228 Acknowledgments Port of Singapore Authority (PSA) Ministry of Education, Singapore Constructive feed-back from referees

29. PADS 200229 References SPaDES/Java homepage http://www.comp.nus.edu.sg/~pasta/spades-java/spadesJava.html Current project webpage http://www.comp.nus.edu.sg/~ngyewkwo/HYP.html MSG homepage http://www.comp.nus.edu.sg/~rpsim/MSG