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A Definition and Classification of Timing Anomalies

A Definition and Classification of Timing Anomalies. Jan Reineke, Björn Wachter, Stephan Thesing, Reinhard Wilhelm Saarland University Ilia Polian, Jochen Eisinger, Bernd Becker University of Freiburg 6 th Intl WORKSHOP ON WCET ANALYSIS Dresden, Germany, July 4, 2006 . Structure.

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A Definition and Classification of Timing Anomalies

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  1. A Definition and Classification of Timing Anomalies Jan Reineke, Björn Wachter, Stephan Thesing, Reinhard Wilhelm Saarland University Ilia Polian, Jochen Eisinger, Bernd Becker University of Freiburg 6th Intl WORKSHOP ON WCET ANALYSIS Dresden, Germany, July 4, 2006

  2. Structure • What are Timing Anomalies? • What is the problem? • Related Work • Definition • Classification WCET' 06, Timing Anomalies, Jan Reineke

  3. Timing Anomalies – Example 1 • Counterintuitive timing behaviour: Local worst-case does not entail global worst-case WCET' 06, Timing Anomalies, Jan Reineke

  4. Timing Anomalies – Example 2 • Counterintuitive timing behaviour: Local worst-case does not entail global worst-case WCET' 06, Timing Anomalies, Jan Reineke

  5. What is the problem? • It makes timing analysis more difficult: The analysis has to follow all possibilities -> exponential blow-up • Goal: • Prove the absence of timing anomalies • Identify conditions for safe local decisions • Need a sound & general definition! WCET' 06, Timing Anomalies, Jan Reineke

  6. Related Work • Giving examples, informal description • Lundqvist & Stenström, `99, `02 • Engblom & Jonsson, `02 • Schneider, `02 • Thesing, `04 • Scheduling Anomalies • Graham, `69 • Necessary condition • Wenzel, Kirner, Puschner, & Riedel, `03, `05 • Limited scope due to underlying assumption WCET' 06, Timing Anomalies, Jan Reineke

  7. Aspects for Definition • Hardware Model • cycle-level behaviour of machine running a program • Abstraction • introduces non-determinism • Locality • what is a local worst-case? • previously ad hoc: cache hit vs. cache miss WCET' 06, Timing Anomalies, Jan Reineke

  8. Hardware Model + Abstraction • Do not model abstraction explicitly: Hardware Model = Maps program to transition system + set of locality constraints • Remark: possible to define correctness condition for abstract model WCET' 06, Timing Anomalies, Jan Reineke

  9. Locality • Locality Constraints: • Local worst-case paths? • Locality Constraints for Micro Operations (IF, M, EX, WB, etc.) WCET' 06, Timing Anomalies, Jan Reineke

  10. Correspondence of Paths Compare „related“ paths only: use Locality Constraints WCET' 06, Timing Anomalies, Jan Reineke

  11. Definition: Timing Anomalies WCET' 06, Timing Anomalies, Jan Reineke

  12. Future Work • Investigate applicability of definition • Automatically identify Timing Anomalies • Prove absence under certain conditions (maybe restricted set of locality constraints) • Abstract VHDL model • Equivalent problem formulation for model checker WCET' 06, Timing Anomalies, Jan Reineke

  13. Classification • Scheduling Anomalies • Speculation Anomalies • Cache Anomalies WCET' 06, Timing Anomalies, Jan Reineke

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