# HW1PlusAnswersnew-1 - Homework I 1 Five jobs are waiting to...

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Homework I 1. Five jobs are waiting to be run. Their expected run times are 9, 6, 3, 5 and X. In what order should they be run in order to minimize average waiting time? (Hint: Though the answer is simple, you need to consider all cases). In class we’ve discussed that shortest job first leads to minimum average waiting time. See class text, p 159. You don’t need to prove it for this question, just remember that fact. In that case the answer is a. 0 < X β 3 : X, 3, 5, 6, 9 b. 3 < X β 5 : 3, X, 5, 6, 9 c. 5 < X β 6 : 3, 5, X, 6, 9 d. 6 < X β 9 : 3, 5, 6, X, 9 e. X > 9 : 3, 5, 6, 9, X 2. This problem deals with real time systems with N CPU’s. Events that real time systems have to respond to are classified as periodic or aperiodic . Consider the first case where jobs occur at regular intervals: Let there be m periodic events and event i occurs with period P i and C i seconds of CPU time are required to handle each event, derive an inequality that can be used to show the conditions under which the periodic load can be handled. ( Hint : Define CPU utilization, ignore context switch overhead.) Utilization is defined as = m i i i P C 1 and this must be less than or equal to N, i.e., CPU utilization cannot exceed the number of CPU’s available, and we have assumed N

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HW1PlusAnswersnew-1 - Homework I 1 Five jobs are waiting to...

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