※ 引述《jim055006 (好崩溃)》之铭言： : (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%) : 这是恐龙本後面的练习题 : 我也看了解答了 : 可是我还是看不懂为什麽 : 答案是 : (a)1/1.1*100=91% : (b)20/21.1*100=94% 先搞清楚单位 每10次IO一次cpu bound 每1ms发出一次IO bound 每次IO BOUBD做完後 要花10ms去完成它 context switch为0.1ms 1.RR=1 因为quantum只有1ms 刚好等於一次IO BOUND 但是换下一个Proces要花0.1的switch 所以1*10+1/1.1*11 2 RR=10 quantum=10ms 但是IO BOUND做不到那麽长就结束了 分子 1*10 //真正运算的时间---------(1) 分母 1.1*10 // 含context switch----(2) 对CPU BOUND而言 因为quamtum=10 所以可以顺利做到完 分子 10*1-----------(3) 分母 10+0.1---------(4) (1)+(3) ------- (2)+(4) 至於题目为何要说10ms後IO COMPLETE 因为他怕没这样说 到时候IO BOUND也跑进来和cpu bound抢工作权 这样计算就不是那麽容易了 可能会有优先权问题 这题印象中有人讨论过 如果找不到题目 其实可以把题目原文贴上google 最後他还是会帮你找回PTT 我都是这做的(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 这题我不会 等其他高手解释罗~ 这题我看到板上有蛮多人问的 : 可是好像都没有很多人回应 : 所以我想在po问一次 : 而且我看恐龙解答也写得很简易 : 所以也是看不太懂 : 以上两题希望大家可以慷慨解囊一下 : 钢温!!! --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 114.38.107.103 ※ 编辑: AIdrifter 来自: 114.38.107.103 (01/17 15:57)