Suzhen Lin, A. Sai Sudhir, G. Manimaran Real-time Computing & Networking Laboratory

1. ConFiRM-DRTS: A CertificationFramework for Dynamic Resource Management in Distributed Real-Time Systems Suzhen Lin, A. Sai Sudhir, G. Manimaran Real-time Computing & Networking Laboratory Department of Electrical and Computer Engineering Iowa State University, USA http://www.ee.iastate.edu/~gmani

2. Outline • Problem statement • Model and certification requirements • The proposed certification framework • Case study of feedback-based scheduling verification • Conclusions

3. Real-time Systems • Logical correctness & timeliness • Real-time tasks have deadlines • Real-time tasks:periodic and aperiodic

4. System Model • Heterogeneous computing nodes • Arbitrary network topology • Periodic and aperiodic workloads • Local scheduler • Global scheduler (load balancer) • Packet scheduler

5. Problem Statement • Problem overview • Certification of dynamic RM • Technical considerations • Virtual homogeneity • Performance • Stability • Verifiability

6. Two Views to Certifiability • How to Certify a given system • Testing, verification, validation • Design for Certifiability • Employ provable techniques and tools

7. DRE Certification Requirements and Certification Techniques/Tools

8. DRE Certification Test-bed

9. Traditional Functional and Performance Testing • Organization • Organize testing into distinct test phases • Observability • Observe the correctness of system behavior • Reproducibility • Get the same results when the program is executed

10. Traditional Functional and Performance Testing ... • Environment Simulation • It mimics the system behavior through test runs • Representativity • System should be represented by realistic inputs • Petri Nets for Verification of RT Systems • Reachability analysis.

11. Virtual Homogeneity Using RTCORBA Each RT-CORBA invocation has a priority. RT Portable Object Adaptor(RT POA) for demultiplexing object requests to the appropriate object skeleton.

12. Certification Techniques on an Object-based Middleware System • Fault Injection Testing • Injecting software faults at compile-time • Injecting software faults at run-time • Interface Mutation Testing • Involves testing interactions between various units. • Testing Through Equivalent Configurations • Involves allowing configurations that are equivalent to those already tested.

13. A Distributed Object Monitoring and Testing System

14. Design Methodology for Verifiability of Feedback Control Scheduling • System Modeling • Controller Design • Model Verification • Scheduler Design • Experimental Evaluation

15. Two-loop Feedback Scheduling • PID Controllers are Used

16. Performances for Control Systems • Overshoot • Settling time • Steady-state error

17. Performances for Scheduling Systems • Goal: to improve ER.

18. Case study—Task Model • Aperiodic soft RT task: • Estimated Execution Time:

19. Case Study—Local Scheduling Systems • Set point: desired MR & RR • Regulated/Measured variable: MR & RR • Control variable: Estimated execution time • Actuator: Execution time estimator • Controller: PI

20. Case Study — Local Scheduling system

21. Stability Analysis for Local System • From Control theory, we get the characteristic equation for the local system in Z domain: • The eigen values of the equation are: • Since , all the eigen values lie within the unit circle, so the local system is stable.

22. Case Study—Global scheduling system • The inner loop responds to changes much more quickly than the outer loop. • So we can treat the local system as a model that has transfer function I (identity matrix). • The analysis of the global system is similar to the local system.

23. Conclusion • Certifying dynamic RM • Very complex process • 100% verification may not be achievable • How to certify a given system • Traditional testing, Validation • Middleware design methodology • Design for Certifiability • Employ mathematically provable techniques • E.g., Feedback control scheduling, Petri nets