Question

Maximum urgency first (MUF) is a real-time scheduling algorithm for periodic tasks. Each task is assigned an urgency that is defined as a combination of two fixed priorities and one dynamic priority. One of the fixed priorities, the criticality, has precedence over the dynamic priority. Meanwhile, the dynamic priority has precedence over the other fixed priority, called the user priority. The dynamic priority is inversely proportional to the laxity of a task. MUF can be explained as follows. First, tasks are ordered from shortest to longest period. Define the critical task set as the first N tasks such that worst-case processor utilization does not exceed 100%. Among critical set tasks that are ready, the scheduler selects the task with the least laxity. If no critical set tasks are ready, the schedule chooses among the noncritical tasks the one with the least laxity.
Ties are broken through an optional user priority and then by FCFS. Repeat Problem 10.3d, adding MUF to the diagrams. Assume that user-defined priorities are A highest, B next, C lowest. Comment on the results.
Consider a set of three periodic tasks with the execution profiles of Table 10.9a. Develop scheduling diagrams similar to those of Figure for this set of tasks that compare rate monotonic, earliest-deadline first, and LLF. Assume preemption may occur at 5-ms intervals. Comment on the results.


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  • CreatedMay 09, 2015
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