Implementing AUTOSAR Scheduling and Resource Management on an Embedded SMT Processor

Transcription

1 Implementing AUTOSAR Scheduling and Resource Management on an Embedded SMT Processor Florian Kluge, Chenglong Yu, Jörg Mische, Sascha Uhrig, Theo Ungerer University of Augsburg 12th International Workshop on Software and Compilers for Embedded Systems April 23-24, 2009 Acropolis, Nice, France AUTOSAR on SMT Kluge et al. 1 / 28

2 Outline 1 Motivation 2 Problems 3 Solution 4 Conclusion AUTOSAR on SMT Kluge et al. 2 / 28

3 Outline 1 Motivation 2 Problems 3 Solution 4 Conclusion AUTOSAR on SMT Kluge et al. 3 / 28

4 Motivation (I) Automotive Software Standards AUTOSAR: AUTOmotive Open System ARchitecture Provides common platform for automotive applications Increases interoperability and interchangeability AUTOSAR on SMT Kluge et al. 4 / 28

5 Motivation (I) Automotive Software Standards AUTOSAR: AUTOmotive Open System ARchitecture Provides common platform for automotive applications Increases interoperability and interchangeability Upcoming Processor Architectures Simultaneous MultiThreading (SMT) Cores Multi-Core Processors real parallelism! AUTOSAR on SMT Kluge et al. 4 / 28

6 Motivation (II) Is AUTOSAR fit for SMT? AUTOSAR on SMT Kluge et al. 5 / 28

7 Motivation (II) Is AUTOSAR fit for SMT? NO! AUTOSAR on SMT Kluge et al. 5 / 28

8 Motivation (II) Is AUTOSAR fit for SMT? NO! What can we do? AUTOSAR on SMT Kluge et al. 5 / 28

9 Motivation (II) Is AUTOSAR fit for SMT? NO! What can we do? How can AUTOSAR benefit from SMT? AUTOSAR on SMT Kluge et al. 5 / 28

10 AUTOSAR Scheduling Basic and Extended tasks Task states: suspended, ready, running, waiting (only extended tasks) AUTOSAR on SMT Kluge et al. 6 / 28

11 AUTOSAR Scheduling Basic and Extended tasks Task states: suspended, ready, running, waiting (only extended tasks) Priority based scheduling: highest priority task is executed Designed for singlethreaded processors AUTOSAR on SMT Kluge et al. 6 / 28

12 AUTOSAR Resource Management Mutual exclusion on resource access Prevent priority inversion and deadlocks Resource access never results in waiting state Priority Ceiling Protocol (PCP) AUTOSAR on SMT Kluge et al. 7 / 28

13 SMT Processor Simultaneous MultiThreading issue instructions of different threads in one cycle Use latencies of one thread to execute another Prioritised slots Real parallelism AUTOSAR on SMT Kluge et al. 8 / 28

14 Challenges Goal: Earlier execution of low-priority tasks Challenges Preserve WCET analysability Preserve externally observable behaviour of highest-priority task Lower-priority tasks can be interrupted by higher-priority tasks! As few changes as possible to standard definition AUTOSAR on SMT Kluge et al. 9 / 28

15 Outline 1 Motivation 2 Problems 3 Solution 4 Conclusion AUTOSAR on SMT Kluge et al. 10 / 28

16 Forward Implementation SMT processor with n thread slots Issue n highest priority tasks Keep execution order Map AUTOSAR task priorities to thread priorities AUTOSAR on SMT Kluge et al. 11 / 28

17 Resource Management and Parallel Execution PCP relies on singlethreaded program execution No prevention from priority inversion and deadlocks in multithreaded program execution AUTOSAR on SMT Kluge et al. 12 / 28

18 Related Work: Resource Management Resource Management for Multiprocessor Systems Multiprocessor Priority Ceiling Protocol Multiprocessor Stack Resource Policy LP-Time Inheritance and Returning AUTOSAR on SMT Kluge et al. 13 / 28

19 Related Work: Resource Management Resource Management for Multiprocessor Systems Multiprocessor Priority Ceiling Protocol Multiprocessor Stack Resource Policy LP-Time Inheritance and Returning No transfer of processing time possible on SMT No nested resource accesses possible AUTOSAR on SMT Kluge et al. 13 / 28

20 Data Synchronisation Scheduler Shared data structures (FIFO queues) NO lock variables available! Further synchronisation necessary AUTOSAR on SMT Kluge et al. 14 / 28

21 Data Synchronisation Scheduler Shared data structures (FIFO queues) NO lock variables available! Further synchronisation necessary Related Work Lamport (Bakery Algorithm), Peterson s Algorithm: Spinning or sleeping/suspending Spinning wastes processing time Suspending can violate task state model AUTOSAR on SMT Kluge et al. 14 / 28

22 Data Synchronisation Scheduler Shared data structures (FIFO queues) NO lock variables available! Further synchronisation necessary Related Work Lamport (Bakery Algorithm), Peterson s Algorithm: Spinning or sleeping/suspending Spinning wastes processing time Suspending can violate task state model Lock-free algorithms Special instructions necessary Compare&Swap or Load Link/Store Conditional AUTOSAR on SMT Kluge et al. 14 / 28

23 Outline 1 Motivation 2 Problems 3 Solution 4 Conclusion AUTOSAR on SMT Kluge et al. 15 / 28

24 Task Filtering Execute only tasks that do not use the same resources Deferred tasks are buffered in task filter Internal task state resource ready Task has highest priority of all tasks accessing the same resources AUTOSAR on SMT Kluge et al. 16 / 28

25 Task Filtering: Example T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 R 1 X R 2 X X R 3 X R 4 X R 5 X X R 6 X X R 7 X X X R 8 X SC o o o o o o AUTOSAR on SMT Kluge et al. 17 / 28

26 Discussion Tasks T 1, T 2, T 3 Priorities P 1 > P 2 > P 3 2 thread slots T 1, T 3 running T 1 and T 2 have resource conflict AUTOSAR on SMT Kluge et al. 18 / 28

27 Discussion (I) No resource conflict between T 2 and T 3 AUTOSAR on SMT Kluge et al. 19 / 28

28 Discussion (II) Resource conflict between T 2 and T 3 on R T 3 non-preemptable AUTOSAR on SMT Kluge et al. 20 / 28

29 Discussion (III) Resource conflict between T 2 and T 3 on R T 3 preemptable T 3 not holding R or other with CP > P 2 AUTOSAR on SMT Kluge et al. 21 / 28

30 Discussion (IV) Resource conflict between T 2 and T 3 on R T 3 preemptable T 3 holding R AUTOSAR on SMT Kluge et al. 22 / 28

31 Consequences Start of high priority tasks may be delayed, but time-predictable Once running, behaviour is same as in single-threaded processor for highest priority task Lower prioritiy tasks: may start earlier, but with lower performance Time for scheduling increases about 100 cycles - total time about cycles (on prototype) Hardware requirement: slot-to-slot interrupt AUTOSAR on SMT Kluge et al. 23 / 28

32 Synchronisation of Scheduler Data Scheduler s FIFO-Queues accessed from every slot Must ensure consistency Use lock-free linked lists HW Requirement: Compare&Swap or Load Link/Store Conditional instructions Work in progress AUTOSAR on SMT Kluge et al. 24 / 28

33 Outline 1 Motivation 2 Problems 3 Solution 4 Conclusion AUTOSAR on SMT Kluge et al. 25 / 28

34 Summary & Conclusion Extensions to AUTOSAR Task Filtering method prevents resource conflicts New state resource-ready introduced Necessary hardware extensions CAS Slot-to-slot interrupts Timing behaviour of highest-priority task is preserved AUTOSAR on SMT Kluge et al. 26 / 28

35 Summary & Conclusion Extensions to AUTOSAR Task Filtering method prevents resource conflicts New state resource-ready introduced Necessary hardware extensions CAS Slot-to-slot interrupts Timing behaviour of highest-priority task is preserved Conclusions Current AUTOSAR not ready for multiprocessing More changes on specification necessary This work is just one step on the road... AUTOSAR on SMT Kluge et al. 26 / 28

36 Future Work Lock-free Algorithms Implementation and evaluation Benchmarking Current benchmarks just look at performance Design benchmark to test resource accesses Integration with Multi-Core Research MERASA project (Multi-Core Execution of Hard Real-Time Applications Supporting Analysability) AUTOSAR on SMT Kluge et al. 27 / 28

37 Thank you! Any Questions? AUTOSAR on SMT Kluge et al. 28 / 28