SFWR ENG 4AA4 Assignment 3 Solutions - Assignment 3 Mectron...

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Assignment 3, Mectron/ Sfwr Eng 4aa4 Sample Solution 1. Briefly explain the following: (a) How are sporadic / aperiodic tasks scheduled by a cyclic execu- tive.[2] The scheduler first schedules the periodic tasks in a frame and if any slack time is available it is given to the next aperiodic task at the head of the aperiodic tasks queue. (b) What do you understand by the term ”Slack Stealing”? [2] If the deadlines of all tasks scheduled in a frame is equal to or greater than the frame size, it does not matter whether the ape- riodic tasks are scheduled at the beginning of the frame or at any other time during the frame as long as they are allowed to run only for the available slack time. Giving preference to run aperi- odic tasks before the periodic tasks in a frame, to utilize the slack time is called slack stealing. (c) What is the purpose of slack stealing? [1] Improve the response time of aperiodic / sporadic tasks. (d) Assume that a cyclic schedule of periodic tasks in a system uses a frame size of 5 and there are 6 frames in the major cycle. Suppose the initial amounts of slack time in frames are 1, 0.5, 0.5, 0.5, 1, 1 respectively. i. An aperiodic task with execution time 3 arrives at time 1. When will it complete its execution if the system does not use slack stealing? [2] 29.5 ii. By how many units of time the response time of the above task can be improved by using slack stealing? [2] 4 time units iii. Now assume that instead of the above task, three sporadic
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