cs6235-5A-rate-mono

cs6235-5A-rate-mono - CS 6235 9/27/2010 Rate Monotonic...

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CS 6235 9/27/2010 Rate Monotonic Scheduler 1 1 CS4220 Embedded Systems CS6235 Real CS6235 Real-Time Systems Time Systems 5A: Rate Monotonic Scheduler Instructor: Calton Pu calton.pu@cc TAs: Qinyi Wu (qxw@cc) Peter Budny (peterb@cc) 2 Rate Monotonic Scheduler Classic hard real-time CPU scheduler Preemption-based Independent tasks Static scheduler: fixed priorities No dynamic priority adjustments Not a static schedule
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CS 6235 9/27/2010 Rate Monotonic Scheduler 2 3 RM Algorithm Main components Periodic tasks, marked by start and end Priority-based preemption Shorter period tasks get higher priority Time line 4 Crucial Zone Theorem Only need to check the first period If tasks make their first deadline, then they can make the following deadlines Time line
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CS 6235 9/27/2010 Rate Monotonic Scheduler 3 5 Discussion of RM Zhao’s evaluation criteria CPU utilization: guaranteed theoretical WCAU limit of 0.693 for CPU Robustness: OK if below the 0.693 limit Timing fault: limited by preemption Aperiodic jobs: high priority until the 0.693 WCAU limit Run-time overhead: may be high 6 Another Discussion Sha’s list of advantages Fixed priorities: easy management Aperiodic tasks: sporadic server, etc Synchronization: priority ceiling, etc Imprecise computations Ease of implementation
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CS 6235 9/27/2010 Rate Monotonic Scheduler 4 7 Transient Overload Variable task CPU consumption
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cs6235-5A-rate-mono - CS 6235 9/27/2010 Rate Monotonic...

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