[OS] CPU utilization

作者: garnettooo (絕代風華賈奈特)   2017-05-17 16:36:01
還想請問大家這題的解析,因為根據題目所提供的情況,
Consider the system running ten tasks and one CPU bound task.Assume that
the I/O bound tasks issue an I/O operation once for every millisecond of
CPU computing and that each I/O operation takes 10 millisecond to complete.
Also assume that the context switching overhead is 0.1 millisecond and
that all processes are long-running tasks. What is the CPU utilization for
RR scheduler when:
(1)time quantum=1 millisecond
(2)time quantum= 10 millisecond
可以了解CPU burst(T)=1, I/O=10,context switch=0.1
(1)第一題沒有問題,因為T=Q,所以CPU utilization=T/S+T=1/1+0.1=1/1.1
(2)第二題我就不太了解為何會有20,畢竟Q=10,Q>T,所以應該是T/S+T=1/1+0.1,
為何會是答案所給的20/21.1呢?
作者: nakabin (日落)   2017-05-17 19:33:00
考完就荒廢了不太確定,不過如果我沒想錯應該是像這樣吧(我假設每個I/O burst tasks一次都只花1mshttp://i.imgur.com/TSTCYoV.jpg糟糕,本來寫T後面不小心寫成P了XD總之那個代表I/O的 叉叉是context switch
作者: garnettooo (絕代風華賈奈特)   2017-05-17 23:03:00
謝謝n大的解答,但想請問一下題目中不是說只有一個cpuBURST跟10個I/O嗎?為何n大的解答是一個I/O+10XCPU呢
作者: nakabin (日落)   2017-05-18 03:19:00
蛤 我寫的意思是一個cpu burst啊 C的那格就是 跑10ms 後面一個一個小格的是I/O 1~10號
作者: garnettooo (絕代風華賈奈特)   2017-05-18 14:50:00
原來如此,感謝

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