Re: [理工] [計組]-台大97-資工
※ 引述《gsrr (下象棋)》之銘言：
: http://www.lib.ntu.edu.tw/exam/graduate/97/97419.pdf
: 第二題
: (d)Suppose that the application runs for 100 seconds when only one
: processor is used , how many seconds would the application requires
: to run on the 8-processor SMP system?
: (e)For the 8-processor run,suppose the disk is transferring data during
: 80% of the execution time.What is the minimal execution time even if
: the system has unlimited number of processors?
: 手上解答為:
: (d) 40 seconds
: (e) 32 seconds
: 想請教各位大大:
: 這兩題題意主要在敘述什麼樣的意思,
: (d)及(e)小題又是如何算出?
: 謝謝!
(d)
前提:
八個處理器下各處理器 IO-TIME = CPU-TIME
解法:
八個處理器加速，但有一半時間做IO加速效果減半
所以加速四倍
(100-IO)/4 = CPU = IO
求得IO = 20 = CPU
所以20 + 20 = 40
(e)
依題意
八個處理器需40秒，時間分配為
0.8*40(IO) + 0.2*40(CPU)
當處理器無限
0.8*40(IO) + (0.2*40)/(很大)(CPU) = 0.8*40(IO) = 32
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