Suzhen Lin, A. Sai Sudhir, G. Manimaran Real-time Computing & Networking Laboratory Department of Electrical and Computer Engineering Iowa State University, USA ConFiRM-DRTS: A Certification Framework for Dynamic Resource Management in Distributed Real-Time Systems

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 Requirements Techniques/Tools R1: Traditional functional and performance testing Test decompostion, observability, reproducibility, environment simulation and representativity R2: Testing of the dynamic resource allocation Petri nets based verification and simulation R3: Virtual homogeneityMiddleware (e.g., CORBA) R4: Verification of Schedulability Feedback control scheduling and simulation R5: Verification of Stability Feedback control theory and simulation

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 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. Certification Techniques on an Object-based Middleware System

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