ISU CPRE 558 - new-rts-lect10 (8 pages)

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Pages:
8
School:
Iowa State University
Course:
Cpre 558 - Real-Time Systems

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CprE 458 558 Real Time Systems Resource Reclaiming CprE 458 558 Real Time Systems G Manimaran 1 Dynamic Scheduling Model Schedulability checking on line by the scheduler Schedule construction on line by the scheduler Dispatching Task execution Resource reclaiming by the processors CprE 458 558 Real Time Systems G Manimaran 2 Resource Reclaiming Resource reclaiming refers to the problem of utilizing resources left unused by a task when it executes less than its worst case computation time The actual computation time of a task can be less than its worst case computation time due to data dependent loops and conditional statements in the task code architectural features of system such as cache hits and branch predictions CprE 458 558 Real Time Systems G Manimaran 3 Resource Reclaiming Contd it is deleted from the current schedule Deletion of a task takes place when extra tasks are initially scheduled to account for fault tolerance it is dropped to make room for more critical tasks CprE 458 558 Real Time Systems G Manimaran 4 Properties of Reclaiming Algorithms Correctness No run time anomaly Inexpensive The overhead cost of a resource reclaiming should be very low compared to tasks computation times Bounded complexity The complexity of a resource reclaiming algorithm should be independent of the number of tasks in the schedule Effectiveness A resource reclaiming algorithm is effective only when its performance is better than that of when no resource reclaiming is used CprE 458 558 Real Time Systems G Manimaran 5 Resource Reclaiming Algorithms Basic Algorithm If there are simultaneous holes in the schedule it can be reclaimed Early Start Algorithm reclaims resources with the condition that if two tasks are nonoverlapping in the pre run schedule then they should not overlap in the post run schedule RV Algorithm Based on a data structure called Restriction Vector RV with Migration Allows task migration from one processor to another CprE 458 558 Real Time Systems G



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