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Toward Energy-Aware Software-Based Fault Tolerance in Real-Time Systems

Toward Energy-Aware Software-Based Fault Tolerance in Real-Time Systems. Osman S. Unsal, Israel Koren, C. Mani Krishna Architecture and Real-Time Systems Laboratory Department of Electrical and Computer Engineering University of Massachusetts, Amherst. The Problem.

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Toward Energy-Aware Software-Based Fault Tolerance in Real-Time Systems

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  1. Toward Energy-Aware Software-Based Fault Tolerance in Real-Time Systems Osman S. Unsal, Israel Koren, C. Mani Krishna Architecture and Real-Time Systems Laboratory Department of Electrical and Computer Engineering University of Massachusetts, Amherst

  2. The Problem • Real-Time (RT) systems are energy and thermal constrained. • Many RT applications run on battery-powered platforms. • RT systems require small form factor. • Fault-Tolerance (FT) is an important design parameter in RT systems. • Many RT applications are life-critical. • Many RT systems operate in hostile (industrial, space) environments. • FT ensures error-free operation in the face of faults.

  3. Fault-Tolerance in RT Systems • Hardware based fault tolerance • Massive redundancy (duplex, TMR) • Requires additional hardware for error checking mechanism • Very power-inefficient • Software based fault tolerance • Application-Level Fault Tolerance (ALFT), an amalgam of time and software redundancy

  4. ALFT Characteristics • Tasks have a primary and secondary copy • Secondaries might be exact copy of primaries, or they could be scaled-down • Resolution reduction • Precision reduction • A secondary task may be aborted if primary successfully finishes execution

  5. The System Model • Distributed RT System • Tasks are periodic, have deadlines • Each primary has one secondary • Primary and Secondaries assigned to separate processors • Concentrating on scheduling, compare w.r.t. EDF • Tasks with random periods, execution-time • Six processor configuration

  6. Energy Model • The more a task executes, the more the energy consumed. • Assumed to linearly scale with the increase in task execution • Appropriate for COTS processors

  7. Overlap

  8. A Simple Energy Saving Heuristic : Shortest Execution-Time First (SEF) Relative Energy Consumption

  9. Another Heuristic: Secondary Execution Time Shifting (SETS)

  10. Case study: Asymmetric Digital Subscriber Line Modem Application

  11. Energy Savings for the ADSL Application

  12. Energy Savings for DifferentSecondary Sizes

  13. Overlap Reduction for DifferentSecondary Sizes (20 tasks)

  14. Overlap Reduction for Different Secondary Sizes (50 tasks)

  15. Effect of Task Granularity on Energy Savings (Secondary Size 80%)

  16. Effect of Task Granularity on Overlap Reduction (Secondary Size 80%)

  17. Summary • An initial analysis into energy-efficiency of various fault-tolerance mechanisms has been made • Power-aware scheduling heuristics for ALFT schemes developed • Current activity: • On-line scheduling heuristics • Power-aware DVS for FT systems

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