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RT Reading Group Meeting 06/27/2002

RT Reading Group Meeting 06/27/2002. Veljko Krunic. Agenda. Introduction Motivation of system System components Gryphon RT-PCIP and EPA DQM Real-Time and OO Q&A. Introduction. Motivation for presenting this papers To understand integrated system

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RT Reading Group Meeting 06/27/2002

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  1. RT Reading Group Meeting 06/27/2002 Veljko Krunic

  2. Agenda • Introduction • Motivation of system • System components • Gryphon • RT-PCIP and EPA • DQM • Real-Time and OO • Q&A

  3. Introduction • Motivation for presenting this papers • To understand integrated system • To understand components on high level • Papers • Are survey of all individual work • Present “Big picture” • This presentation is continuation of Sam’s presentation • Discussion of OO in context of Real Time

  4. Motivation • Multiperson distributed virtual environment • Supports multiperson communication • Plus domain specific tools • World consists of • Objects • Avatars • Form of telepresence

  5. Motivation (Cont) • Presents challenges • Graphics rendering • Continues media • Distributed objects • Movement of large amount of data • Applications • Thread schedulability and resource management • Dynamic negotiations • Integrates all previous work of all team members

  6. Gryphon • Distributed object manager • Caching • Cache coherence • Works in cooperation with applications • Object types • Private-local • Shared-local • Shared-nonlocal • Global

  7. Object Location • Constrained by access times • Caching policy • Refreshment frequency • Bandwidth requirements • Known best by application • Application negotiates • Consistency update policy • Object location

  8. Gryphon and CORBA • CORBA • Distributed object access & RPC • Parameter marshalling • ORB implements coordination • Gryphon compared to • Centralized object manager • ORB centralized CORBA • ORB distributed CORBA • Gryphon provides significant improvements

  9. RT-PCIP • Device-to-device pipeline architecture • Standardized source and sink • Filters could be inserted • EPA • Dynamic priority computation in overloaded system • EPA is based on DM tests • Uses expected time with probability distribution • WCET is statistical problem here

  10. Dynamic QoS Manager • Framework for QoS guarantees among processes • Process info are based on triples • Execution level • Resource • Benefit • Plus • Maximum benefit • Maximum CPU usage • Number of execution levels

  11. Resource Allocation Policies • Distributed • Missing deadline changes execution level of that process • Fair • Missing deadline reduces level of application using most of CPU (even) or that has lowest benefit/CPU ratio (proportional)

  12. Resource Allocation Policies • Distributed • Missing deadline changes execution level of that process • Fair • Missing deadline reduces level of • Application using most of CPU (even) • Application that has lowest benefit/CPU ratio (proportional)

  13. Resource Allocation Policies (Cont) • Optimal • Maximize overall user benefit • Good for initial allocations • Causes a lot of fluctuation • Artificial parameter added to tame fluctuations • Hybrid • Optimal for initial allocations • Different algorithms from that point on

  14. DQM Limitations • User space implementation • Based on cooperation from applications • Could not control rogue applications • What if application estimates are wrong • Fluctuations and resonance • Requires dynamic refinement • Based on weight factor • What about more complicated models of load?

  15. OO and Hard Real Time • Subject of personal interest • Discussion of OO • Design by contract • Preconditions, postconditions and invariance • Combination with Hard Real Time • Based on some discussions and article in DDJ

  16. Design by Contract • OO technique invented by Bertrand Meyer • Eiffel • Each method operates with guarantees • Precondition – this must be guranteed before I am called • Postcondition – if preconditions are met, this is my guarantee • Invariance – object of this class always has this

  17. Design by Contract (Cont) • Example: y = sqrt(x) • Precondition x > 0 • Postcondition: x == y*y • Exception is thrown if precondition or postcondition is violated

  18. Design by Contract and RT • Based on the article in DDJ • Extend preconditions and postcondition on timings • Automatic watchdog per thread • Could be done in C/C++ • Similar work done by Adam • Limited timer resolution unless on scheduler level • Testing paradigm, not RT concept • Are there benefits in allowing thread to address exception in its context?

  19. Some Techniques for Multiprogramming • Quick summary • Presentation I made in the JD Edwards

  20. Summary • High level system description • Summary of individual works • Some OO and distributed programming mix

  21. Q&A

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