Fault tolerance techniques for real time operating system
- 1. FAULT TOLERANCE TECHNIQUES FOR REAL TIME OPERATING SYSTEM Seminar Coordinator: Ms SAUMYA SADANANDAN Guided by: Mr MELBIN VARGHESE JOHN Prepared by: ANU MARIA K JOSE S7,IT 1
- 2. OUTLINE 2 INTRODUCTION PROBLEM STATEMENT FEATURES OF REAL TIME OPERATING SYSTEMS DEADLINE RTO FEATURES AND FAULT TOLERANCES MEMORY MANAGEMENT KERNEL CONSIDERATIONS PROCESS AND THREAD MANAGEMENT SHEDULING COMMUNICATION I/O MAMAGEMENT PROGRAMMING LANGUAGES CONCLUSION INVITING QUESTIONS THANK YOU
- 3. INTRODUCTION 3 Operating system: It acts as an intermediary between the user of a computer and the computer hardware. Fault Tolerance: A property that enables a system continue operating even in the presence of a failure Real Time Systems: Systems with well defined fixed time constraints.
- 4. INTRODUCTION continued….. 4 Nowadays operating systems are inseparable part of computer systems. RTOSs are widely used in safety-critical domains. Hence, fault tolerance is an essential requirement of RTOSs employed in safety-critical domains.
- 5. PROBLEM STATEMENT 5 In safety critical domains all the system’s requirements should be met and a catastrophe occurs if the system fails. Thus, the operating systems employed in safety-critical domains should produce correct and valid results in the presence or in the absence of faults.
- 6. FEATURES OF REAL TIME OPERATING SYSTEM 6 Real time operating systems emphasize predictability, efficiency and include features to support timing constraints. All tasks should be released on time and also should be completed before particular times called deadline Violating time constraints leads to system failure
- 7. DEADLINES 7 It is the instance when the results should be produced before it. Deadlines can be: Soft : If a result has a utility even after the deadline has passed Firm : If a result has no utility even after the deadline has passed Hard: If severe consequences would result if a firm deadline is missed
- 8. REAL TIME OPERATING SYSTEM FEATURES AND FAULT TOLERANCE TECHNIQUES 8
- 9. 1.MEMORY MANAGEMENT 9 In order to protect operating systems components, fault tolerance begins with memory protection. The use of DSA(Dynamic Storage Allocation) leads to uncertainty in RTOS. FAULT TOLERANCE TECHNIQUES: TLSF Algorithm bitmaps
- 10. 1.2 MEMORY MANAGEMENT UNIT 10 Some RTOSs disable MMU causing all processes to run in the same address space. This may lead to the creation of some bugs which can then lead to system crash. FAULT TOLERANCE TECHNIQUE: Enable MMU
- 11. 1.3 REDUNDANCY 11 Redundancy is one of the most important techniques in fault tolerance. When a process is loaded, the operating system duplicates its data and states in more than one place/memory. Whenever the task wants to read data from memory, a voting is done on replicas.
- 12. 1.4 ERROR CORRECTING CODE MEMORY 12 It is an instrument to improve operating systems reliability. It is a type of computer data storage that has ability to detect and correct many kinds of internal data corruption. Some non-ECC memories with parity support allows errors to be detected, but not corrected. The reliability of a fault-tolerant RTOS would be improved by employing this kind of memory.
- 13. 2. KERNEL CONSIDERATIONS 13 The kernel of a fault-tolerant RTOS must be as follows: Should provide a mechanism that whenever an error occurs, a notification is sent to an agent. The agent then has the duty to perform some types of error recovery actions. This agent is called supervisor and must be run in an isolated address space
- 14. KERNEL CONSIDERATIONS continued…… 14 FAULT TOLERANCE TECHNIQUE: Event logging mechanism software watchdog capability Should protect themselves against improper invoking system calls and passing invalid parameters. Availability for dependable computing Should prevent the spread of faults to the kernel
- 15. 3. PROCESS AND THREAD MANAGEMENT 15 Process definition and activation is one of the most important roles of RTOSs. RTOSs should activate a process once and release it once or periodically . It must also guaranty each release is started on-time and is finished before its deadline.
- 16. PROCESS AND THREAD MANAGEMENT continued…. 16 If tasks’ behavior is not monitored and controlled by the RTOS: a task may, as a result of malicious or careless execution of another task, cannot use processor or other system resources. other tasks may fail because of their inability in acquiring required resources and resulting in deadline miss.
- 17. PROCESS AND THREAD MANAGEMENT continued…. 17 One possible solution is to reserve required resources for each process. In fixed-priority systems, tasks’ priority would be changed incorrectly because of fault occurrence in process table. A possible technique to solve this problem is to acquaint process manager with the importance of the tasks by using partitions in the memory.
- 18. 4. SCHEDULING 18 If several processes are run at the same time then the system has to choose among them. This decision is called CPU scheduling. Some of the important sheduling algorithms used in real time system are: Rate Monotonic(RM) Earliest Deadline First(EDF) Least Laxity First(LLF)
- 19. SCHEDULING continued…….. 19 If the scheduler fails, other system tasks are not scheduled and released correctly and as result the system crashes. FAULT TOLERANCE TECHNIQUES: pre-constructed static scheduling table. N-copy programming (NCP) . take the required time to handle faulty tasks into its time analyses fault-tolerant RTOSs should be able to recover processors from transient and permanent faults too.
- 20. 5. I/O MANAGEMENT 20 Deals with the management of I/O accesses such that interference is prevented and tasks are completed in time. Fault-tolerance RTOSs must provide some fault tolerance techniques to tolerate faulty I/O devices. FAULT TOLERANCE TECHNIQUES: Replication Robustness
- 21. PROGRAMMING LANGUAGES 21 Special programming languages should be employed to meet RTO requirements. It must also guaranty correct responses within strict timing constraints. It should also support some error detection and error correction techniques. Some characteristics to be followed by RTOS programming languages are: well-defined language semantics, the strong type checking, structuring mechanisms.
- 22. CONCLUSION 22 Real-time operating systems are widely used in safety- critical domains. Safety-critical system: if the occurrence of a failure in meeting system requirements causes to catastrophic effects. The costs of a system failure leads to catastrophe and exceeds the initial investment in the computer and in the controlled object
- 23. REFERENCES 23 An Overview of Fault Tolerance Techniques for Real-Time Operating Systems : Reza Ramezani,Yasser Sedaghat Operating system concepts :A. Silberschatz, P. B. Galvin, and G. Gagne, J. Wiley & Sons, 2009 Principles of memory management- https://www.cs.drexel.edu/~bls96/excerpt3.pdf Dependable computing and fault tolerance-Jean Claude Lapris TLSF: a New Dynamic Memory Allocator for Real-Time Systems∗ M. Masmano, I. Ripoll, A. Crespo, and J. Real Universidad Polit´ecnica de Valencia, Spain. en.wikipedia.org/wiki/Fragmentation_(computing) http://www.slideshare.net/Tech_MX/real-time-os
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