Real-Time Operating Systems

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Scheduling: definition ¿ Given a set of tasks J = {J 1 , ...J n } a schedule is an assignment of tasks to the processor so that each task is executed until completion. ¿ Formally: ¿ A schedule is a function σ : R+ → N such that: ¿ ∀t ∈ R +, ∃ t 1 , t 2 ∈ R +, ∀t∈ [t 1 ,t 2 ) σ(t) = σ(t‘) ¿ In practice, σ is an integer step function σ(t) = k means task J k is executing at time t, σ(t) = 0 means CPU is idle ¿ Each interval [t i ,t i+1 ) with σ(t) constant for t ∈ [t i ,t i+1 ) is called a time slice 31 Scheduling: example ¿ A schedule is called feasible if all tasks can be completed according to a set of specified constraints ¿ A set of tasks is called schedulable if there exist at least one algorithm that can produce a feasible schedule ¿ Example: 32 16
Scheduling constraints ¿ The following types of constraints are considered: ¿ Timing constraints • meet your deadline ¿ Precedence constraints • respect prerequisites ¿ Resource constraints • access only available resources 33 Timing constraints ¿ <strong>Real</strong>-time systems are characterized mostly by timing constraints ¿ Typical timing constraint: deadline ¿ Deadline missing separates two classes of RT systems: ¿ Hard : missing of deadline can cause catastrophic consequences ¿ Soft : missing of deadline decreases performance of system 34 17
Page 1 and 2: Real-Time Operating Systems 1 Summa
Page 3 and 4: ¿ Real-time Introduction (3) ¿ Ti
Page 5 and 6: RTOS 9 Real-time Operating Systems
Page 7 and 8: Real-time Operating Systems (3) ¿
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: Processes ¿ Called tasks in the RT
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

Real-Time Operating Systems

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