[理工] [OS] 99交大資聯OS第19題

看板Grad-ProbAsk作者dacvidania (妖精鄉騎士)時間13年前 (2011/01/17 18:56)推噓1(1推 0噓 24→)

留言25則, 5人參與討論串1/2 (看更多)

19.Consider that a system scheduls three processes P1,P2,P3 using Round-robin with time quantum=2 units of time. These three processes arrive in the order P1,P2,P3, all ready at time 0. The three processes share a resource R, which is protected by a mutex lock. The first process P1 runs 3 units of time, block the resource R 3 units of time,unlocks this resource,and then runs 1 unit of time before it completes. Let this execution of P1 be denoted by {3,R(3),1}. The execution of the second process P2 and the third process P3 are denoted by {2,R(1),3} and {2,R(2),2}, respectively. Let waiting queues be FIFO. which one(s) of the following is(are) true? A. The total number of context switches is not less than 9. B. T2 has the longest turnaround time. C. Decreasing P1's execution time from {3,R(3),1} to {3,R(1),1} reduces P2's turnaround time. D. Increasing P1's execution time from {3,R(3),1} to {4,R(3),1} reduces P2's turnaround time. 答案給ACD 但我自己算是只有A對 @@ 原本: | P1 | P2 | P3 | P1 | P2 | P3 | P2 | P1 | time 0 2 4 5 6 7 8 9 11 12 13 ^^^ ^^^^^^^^^^^^^^^^ R(1) R(2) R(3) time4~5 P2執行R(1) time6~8 P3執行R(2) time8~11 P1執行R(3) (C)選項的結果和原本一樣，P2的turnaround time沒變 (D)選項: P2的turnaround time增加 | P1 | P2 | P3 | P1 | P2 | P3 | P2 | P1 | time 0 2 4 6 8 10 12 13 14 不知道我哪裡算錯.. 有高手可以幫我解答嗎... 感恩 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 114.34.133.127

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