推 jim055006:太感激了!!!....講得太詳細了 01/17 22:14
→ lanlansaysay: 看了很久還是不太懂QQ 04/13 22:07
※ 引述《jim055006 (好崩潰)》之銘言：
: (1)
: [CPU Scheduling] Consider a system running ten I/O-bound 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 milliseconds
: to complete. Also assume that the context switching overhead is 0.1
: milliseconds
: and that all processes are long-running tasks. What is the CPU utilization
: for a
: Round-robin scheduler when:
: (a) The time quantum is 1 millisecond (5%)
: (b) The time quantum is 10 milliseconds (5%)
: 這是恐龍本後面的練習題
: 我也看了解答了
: 可是我還是看不懂為什麼
: 答案是
: (a)1/1.1*100=91%
: (b)20/21.1*100=94%
先搞清楚單位
每10次IO一次cpu bound
每1ms發出一次IO bound 每次IO BOUBD做完後 要花10ms去完成它
context switch為0.1ms
1.RR=1
因為quantum只有1ms 剛好等於一次IO BOUND
但是換下一個Proces要花0.1的switch
所以1*10+1/1.1*11
2 RR=10
quantum=10ms 但是IO BOUND做不到那麼長就結束了
分子 1*10 //真正運算的時間---------(1)
分母 1.1*10 // 含context switch----(2)
對CPU BOUND而言 因為quamtum=10 所以可以順利做到完
分子 10*1-----------(3)
分母 10+0.1---------(4)
(1)+(3)
-------
(2)+(4)
至於題目為何要說10ms後IO COMPLETE
因為他怕沒這樣說 到時候IO BOUND也跑進來和cpu bound搶工作權
這樣計算就不是那麼容易了 可能會有優先權問題
這題印象中有人討論過
如果找不到題目 其實可以把題目原文貼上google
最後他還是會幫你找回PTT 我都是這做的(汗
: --------------------------------------------------------------------------------
: (2)
: [File-System Implermentation] Consider a file system on a disk that has both
: logical and physical block sizes of 512 bytes. Assume that the information
: about
: each file is already in memory. For each of the three allocation strategies
: (contiguous, linked, and indexed). answer these questions:
: (a) How is the logical-to-physical address mapping accomplished in this system?
: (For the indexed allocation, assume that a file is always less than 512
: blocks long.)
: (b) If we are currently at logical block 10 (the last block accessed was block
: 10) and want to access logical block 4, how many physical blocks must be
: read from the disk?
:
恩 很抱歉 這題我不會 等其他高手解釋囉~
這題我看到板上有蠻多人問的
: 可是好像都沒有很多人回應
: 所以我想在po問一次
: 而且我看恐龍解答也寫得很簡易
: 所以也是看不太懂
: 以上兩題希望大家可以慷慨解囊一下
: 鋼溫!!!
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※ 編輯: AIdrifter 來自: 114.38.107.103 (01/17 15:57)