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Integrated Real-Time Systems

Integrated Real-Time Systems. Vibhooti Verma M.Tech . (CSE) 05305016. Advisor: Prof. Krithi Ramamritham. Outline. Introduction Focus of the Work and Motivation Contributions SParK/SCOS: System Requirements SParK: System Architecture SParK: Design Issues Scheduling

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Integrated Real-Time Systems

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  1. Integrated Real-Time Systems VibhootiVerma M.Tech. (CSE) 05305016 Advisor: Prof. KrithiRamamritham

  2. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • I/O Virtualization • CPU Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  3. Introduction to Integrated Real-Time Systems (IRTS) • Applications with different levels of criticality • Hard real-time, Soft real-time, Non real-time • Tasks with different arrival patterns • Aperiodic, Periodic • Strong Partitioning • Spatial and Temporal partitioning • A Typical System:

  4. Focus of Our Work • Design and development of a Strongly Partitioned real-time Kernel(SParK) which can host multiple RTOS (one of them being Safety Critical Operating System (SCOS) Motivation • Fault Containment • Easy Verification and Validation • Application Specific Operating System • Local Schedulability Analysis • Efficient Utilization of Resources

  5. Contributions • Identified system components and proposed system architecture • Designed SParK ensuring strong partitioning based on virtualization concepts • Proposed Rate Monotonic based partition scheduler to achieve temporal partitioning • Identified the problem of Partition Inversion and proposed solution for the same • Adopted Virtual Interrupt Partition to avoid deadline miss due to interrupt storm • Implemented in Stand-Alone RTLinux: • Two-level static cyclic scheduler • Two-level dynamic scheduler • Interrupt Server • Priority Inheritance • Serial Port driver

  6. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • I/O Virtualization • CPU Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  7. SParK: Requirements • Strongly partitioned architecture • Temporal and Spatial partitioning • Fault Containment and Isolation • Multiplex system resources among different partitions • Support partitions with different RTOS • Provide Inter-Partition Communication mechanism • Guarantee Interrupts to meet their deadlines • Simple design • Diskless system • Full Predictability

  8. SCOS: Requirements • Interface to hardware • Task Management and priority based scheduling • Inter-task communication • Interrupt Management • Memory management with protection • Timer Services • I/O Services • Scalable, Portable • Support for embedded diskless target environment (ROMable)

  9. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • I/O Virtualization • CPU Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  10. SParK: System Architecture • Salient Features • SParK layer between RTOS and Hardware • Virtual Aperiodic Partition (VAP) • Virtual Interrupt Partition (VIP) • Virtual Device Partition (VDP)

  11. Virtualization and SParK • Similarities • Running multiple OS(RTOS) • Spatial Partitioning • Isolation and Fault containment • VMM (SParK) acts as resource manager • VMM (SParK) gives an illusion to guest OS that they have exclusive access to resources • Differences • Temporal partitioning • Inter-partition communication • Interrupt Guarantees without affecting tasks

  12. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • I/O Virtualization • CPU Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  13. Scheduling: Issues • Ensuring temporal partitioning • All real-time tasks of all the partitions should meet their deadlines. • Mechanism to handle Partition Inversion • Minimizing partition switch overhead • Handling aperiodic tasks • Ensuring ‘n’ out of ‘m’ interrupts without affecting other tasks

  14. Scheduling: Approach • Two-level hierarchical scheduler • Lower level scheduler schedules partitions • Upper level scheduler schedules tasks within the partition • Lower level scheduler can adopt • Static cycle scheduling • RM based priority scheduling (proposed) • EDF based Dynamic Open environment scheduling • Upper level can have any fixed priority scheduling

  15. Scheduling: Techniques • SPIRIT’s Cyclic Scheduling [1] • Non-preemptable sections not handled in original algorithm, proposed solution for same and modified schedulability bounds • Separate partition for aperiodic tasks • Open Environment ‘s Dynamic-Priority-Driven (EDF) Scheduling [2] • CBS and TBS for partition scheduling • Handling Aperiodic tasks not clear • Handling Blocking factor with TBS only • RM Based Priority Scheduling • Handles non-preemtable section • Modified schedulability bounds to account for non-preemptable sections • Least priority partition for aperiodic tasks

  16. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • I/O Virtualization • CPU Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  17. Static Cycle Driven Scheduling Algorithm at lower level • Allocates capacity and cycle time for every partition • Creates a static schedule, uses Unique and Harmonic cycle approach • Separate VAP with dynamic slot shifting to provide better responsiveness to aperiodic tasks

  18. Schedulability Condition • If a partition has ‘n’ tasks with computation time Cj, deadline Dj and period Pj, and assigned processor capacity , then a task is schedulable if Inactivity period of a task is Minimum activity period of a partition is A Partition is schedulable if: 1.It is schedulable at processor of speed 2.Partition cycle

  19. Example: Static cycle scheduling of partitions

  20. Partition Inversion • Definition: scenario where a scheduled partition gets blocked due to locks held by other partition(s) • Our solution: Let the partition finish all of its CS before partition switch

  21. Partition Inversion: Modified Schedulability Bounds • Maximum duration to complete a partition Pk’s critical section Unique Partition cycle approach: every partition gets scheduled exactly once hence modified schedulability bounds

  22. RM based Preemptive Priority scheduling (RMSParK) • If there are ‘m’ partitions with feasible for ith partition then all partitions are schedulable if Where, lower the , higher the priority

  23. Handling Partition Inversion in RMSParK Partition preemption: 1)Budget exhaustation 2)Arrival of higher priority partition • Current partition has to let other partitions finish their critical sections: • When it is scheduled for the first time in its period • When other higher priority partition preempts it and starts executing Using RMA exact analysis for partition scheduling taking blocking into account: • If Pn is highest priority partition otherwise Generalized formula for ith response time of a nth partition

  24. Infinite Partition Inversion

  25. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • I/O Virtualization • CPU Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  26. Interrupt Handling • Requirement: To guarantee min. ‘n’ number of interrupts, in a particular partition will be served with bounded delay at any given point of time • Proposed Approach: Virtual Interrupt Partition(VIP) • Separate partition which is assigned processor capacity and partition cycle according to interrupt characteristics • Interrupts are served when VIP has budget otherwise deferred till next replenishment • Static Cycle Scheduling • RM based priority scheduling

  27. Timer Virtualization • Issues • Maintaining time in deactivated partition • Guest RTOSs sharing same timer device demand different timer resolution

  28. Timer Virtualization • Our Approach: Paravirtualization • No virtual interrupt generation for deactivated partition • Update real time in guest RTOS when scheduled • Timer interrupt delivery to active partition • Sudden increase in time but fine if tasks are schedulable • Simple with lesser overhead

  29. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • CPU Virtualization • I/O Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  30. CPU Virtualization • Challenges • Non –virtualizable CPU architecture • Instructions which do not trap when run in unprivileged mode (POPF) • Unprivileged instructions let the CPU access privileged state • Techniques • Full Virtualization • On-fly binary translation • Paravirtualization • Replacement of problematic instruction

  31. CPU Virtualization • Our Approach: Paravirtualization • Emulation for privileged instruction in SParK for guest RTOS • Replacement of non-virtualizable instruction by hypercalls • Trap source Identification • Memory Location Trekking • SParK in ring 0 and Guest OS in ring 1 and user application in ring 3

  32. I/O Virtualization • Issues • One device, multiple drivers results in inconsistent device state • Device driver’s location • If in SParK, fault containment violated • If in guest RTOS, mechanism to service other partition's • Accounting time for device access • I/O virtualization technique should also ensure • Fault Containment • Isolation • Responsiveness • Unmodified Device Driver Reuse • SParK’s simplicity

  33. I/O Virtualization • Our Approach: Split Driver Architecture

  34. Memory Virtualization • Issues • Spatial Partition among partitions • No interference to SParK • Architecture specific • Our Approach • Static memory allocation using segmentation at compile time for all the partition

  35. Inter-partition Communication • Issues • Safe communication mechanism to satisfy isolation among partitions. • Minimum SParK’s involvement to reduce overhead • Our Approach • Asynchronous notification through event channel • Shared page for data transfer and information of grated page kept in SParK • Budget accounted on requesting partition

  36. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • CPU Virtualization • I/O Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  37. Implementation • Priority inheritance (changes in synchronization primitives) • Serial Port Driver • Interrupt Server • Two-level Hierarchical scheduling • Static Cycle Driven • Budget Lending • Dynamic EDF based

  38. Outline • Introduction • Focus of the Work and Motivation • Contributions • SParK/SCOS: System Requirements • SParK: System Architecture • SParK: Design Issues • Scheduling • Two-level Static cycle and RM based priority scheduling • Partition Inversion and Solution • Virtual Aperiodic Partition • Interrupt handling • Virtual Interrupt Partition • Timer Virtualization • CPU Virtualization • I/O Virtualization • Memory Virtualization and Inter- Partition Communication • Implementation • Conclusions and Further Work

  39. Conclusion • We presented complete design of SParK • We proposed: • Modifications in virtual machine techniques for virtualizing resources to meet real-time constraints • RM based preemptive priority partition scheduling • Modifications in integrated real-time scheduling algorithms to consider non-preemptable section • Virtual Interrupt Partition • Virtual Aperiodic Partition • We implemented in SARTL • Two-level static cyclic scheduler • Two-level dynamic scheduler • Interrupt Server • Priority Inheritance • Serial Port driver

  40. Future Work • Look into architecture specific issues for memory allocation and other hardware initialization • Implementation of various hypercalls to act as interface between guest RTOS and SParK • Porting guest RTOS to SParK by replacing problematic instructions in it by appropriate hypercalls • Front-end device drivers for guest RTOSs • Ethernet driver for Stand-Alone RTLinux towards building SCOS • Prototype Implementation of SParK

  41. References • Daeyoung Kim. Strongly Partitioned System Architecture For Integration Of Real-Time Applications. PhD thesis, UNIVERSITY OF FLORIDA, 2001 • Zhong Deng, Jane W.-S. Liu, Lynn Zhang, Seri Mouna, and Alban Frei. An open environment for real-time applications. Real-Time Systems, 16(2-3):155{185, 1999 • Mendel Rosenblum and Tal Garnkel. Virtual machine monitors: Current technology and future trends. IEE Computer Magazine, May 2005 • Tullio Facchinetti, Giorgio Buttazzo, Mauro Marinoni, and Giacomo Guidi. Non-preemptive interrupt scheduling for safe reuse of legacy drivers in real-time systems. In ECRTS '05, pages 98-105, Washington, DC, USA, 2005. IEEE Computer Society • Paul Barham, Boris Dragovic, Keir Fraser, Steven Hand, Tim Harris, Alex Ho, Rolf Neugebauer, Ian Pratt, and Andrew Wareld. Xen and the art of virtualization. In SOSP '03, pages 164{177, New York, NY, USA, 2003. ACM Press

  42. Timer Virtualization • Full Virtualization: • Virtual interrupt generation • VM Time tracker • Fast Catchup • Time synchronization tool when fast catchup is impossible

  43. I/O Virtualization

  44. VM Environment Vs SParK

  45. Comparison of RTOS

  46. Comparison of various scheduling policies

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