Real-Time Operating Systems

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Real-time Operating Systems (2) ¿ Desirable features of a RTOS: ¿ Timeliness • OS has to provide mechanisms for: • time management • handling tasks with explicit time constraints ¿ Predictability ¿ Fault tolerance ¿ Design for peak load ¿ Maintainability 11 RTOS evaluation metrics ¿ Interrupt latency (T il ): ¿ the time from the start of the physical interrupt to the execution of the first instruction of the interrupt service routine ¿ Scheduling latency (interrupt dispatch latency) (T sl ): ¿ the time from the execution of the last instruction of the interrupt handler to the first instruction of the task made ready by that interrupt ¿ Context-switch time (T cs ): ¿ the time from the execution of the last instruction of one user-level process to the first instruction of the next user-level process ¿ Maximum system call time: ¿ should be predictable & independent of the # of objects in the system 12 6
Real-time Operating Systems (3) ¿ Timeliness ¿ Achieved through proper scheduling algorithms • Core of an RTOS! ¿ Predictability ¿ Affected by several issues: • I/O & interrupts • Synchronization & IPC • Architecture • Memory management • Applications • Scheduling! 13 Achieving predictability: interrupts ¿ One of the biggest problem for predictability ¿ Typical device driver: ¿ In most OS: • interrupts served with respect to fixed priority scheme • interrupts have higher priorities than processes Æ problem in real-time systems: • processes may be of higher importance than I/0 operation! 14 7
Page 1 and 2: Real-Time Operating Systems 1 Summa
Page 3 and 4: ¿ Real-time Introduction (3) ¿ Ti
Page 5: RTOS 9 Real-time Operating Systems
Page 9 and 10: Achieving predictability: interrupt
Page 11 and 12: Priority inversion (2) ¿ Basic pri
Page 13 and 14: Achieving predictability: memory ma
Page 15 and 16: Processes ¿ Called tasks in the RT
Page 17 and 18: Scheduling constraints ¿ The follo
Page 19 and 20: Periodic and aperiodic tasks ¿ Per
Page 21 and 22: Real-time scheduling 41 ¿ Given: S
Page 23 and 24: Scheduling metrics ¿ n tasks ¿ Av
Page 25 and 26: Jackson’s algorithm [1955] ¿ 1 |
Page 27 and 28: Horn’s algorithm ¿ Example: 53 S
Page 29 and 30: Introduction ¿ Periodic activities
Page 31 and 32: Processor utilization factor (2) ¿
Page 33 and 34: Cyclic executive approach ¿ Schedu
Page 35 and 36: Process-based scheduling ¿ Fixed-p
Page 37 and 38: RM schedulability test (2) ¿ For l
Page 39 and 40: EDF algorithm ¿ Dynamic scheduling
Page 41 and 42: Deadline monotonic (DM) scheduling
Page 43 and 44: EDF for D
Page 45 and 46: Periodic task scheduling: summary D

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