Re: [理工] [計組]95東華資工

看板Grad-ProbAsk作者wheels時間14年前 (2011/11/28 18:07)推噓3(3推 0噓 3→)

留言6則, 4人參與討論串2/2 (看更多)

※ 引述《seacottobaby (海綿寶寶)》之銘言： : We make an enhancement to a computer that improves some mode of execution : by a factor of 10. Enhanced mode is used 80% of the time,measured as a : percentage of the execution time when the enhanced mode is in use. : (1) What is the speedup we have obtained from fast mode? : Ans : Speedup = Time(unenhanced) / Time(enhanced) : The unenhanced time is the sum of the time that does not benefit from : the 10 times faster speedup,plus the time that does benefit , but before : its reduction by the factor of 10. Thus : Time(unenhanced) = 0.2 X Time(enhanced) + 10 X 0.8 X Time(enhanced) : = 8.2 Time(enhanced) : 我不太了解解答的意思... 為什麼不是 speed = 1 / ( (0.8/10) + 0.2 ) 這樣? 因為題目有陷阱，它給的80%是在enhanced mode底下的execution time之80%為加速的部分。若令enhanced mode之execution time為x，則0.2x為在enhanced mode下沒有被加速的部分，這個部分會跟unenhanced mode所需花的時間一樣。所以unenhanced mode總共的execution time為0.2x + 0.8x * 10 0.8x * 10 是為了把加速完的部分還原回來。畫個圖就很清楚了 ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇▇▇▇▇▇　　unenhanced execution time ^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 無法被加速　　　　　　可被加速 (此區塊不變) ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇ enhanced execution time = x ^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^ 無法被加速被加速完 0.2x 0.8x -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.112.30.136

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genius945

11/28 23:08, , 1^F

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mqazz1

11/29 00:12, , 3^F

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