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Lecture Topic: Real Time CPU scheduling
Material up to 5.27 on the slides will be on the midterm
Multilevel Feedback Queue: A process can move between multiple queues Get from slides (?)
Real Time CPU scheduling Can present challenges Soft real time systems: Critical real time tasks have the highest priortiy but there are no guarantees Hard real time systems: Tasks need to be scheduled first (?)
Event Latency: The amount of time that elapses from when an event occurs to when it is serviced Two types of latency's affect performance:
- Interrupt latency
- Dispatch Latency
Dispatch latency conflicts:
- You need to preempt any processes running in kernel mode
- Release by low priority processes of resource needed by high priority processes
Priority based scheduling: For real time scheduling, you need to support preemptive, priority based scheduling, but this only guarantees soft real time For hard real time, must also provide ability to meet deadlines: Processes have new characteristics, periodic ones require CPU at constant intervals:
- has processing time t, deadline of d, and a period p
- 0 < t < d < p
- rate of period task is 1/p
Rate monotonic Scheduling: A priority is assigned based on the inverse of its period. Shorter periods = higher priority longer periods = lower priority
Earliest deadline first: Priorities are assigned according to deadlines: The earlier the deadline, the higher the priority The later the deadline, the lower the priority
Algorithm Evaluation: (?)
Midterm Review:
Midterm is balanced: Applying tools relevant to concepts Answering theory questions About 60% of the grade is theory (no coding) 50 minutes
Understanding the labs and stuff under misc. in d2l should be enough
Topics to review: Slides (Chapter 1 to Chapter 5, until rate monotonic scheduling) Lab 2 and Lab 3 A1 and A2 Content of the misc. useful stuff folder Scheduling, metrics Materials occurring multiple times in the lectures
How to answer if you don't know If you remember the book answer - use that answer in your own words if you are trying to explain a concept the book is the most reliable source
What would the output of the following function will probably be on the midterm