※ 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!!! --

※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 114.38.107.103 ※ 編輯: AIdrifter 來自: 114.38.107.103 (01/17 15:57)