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計算機結構與作業系統(B)

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國立臺灣大學 2022 · 考試 · 第 15 題

(5 pts) Assume the CPI for INT instructions, FP instructions, L/S instructions, and branch instructions for a given processor P is 1, 2, 4, and 2, respectively. Consider a program F that includes $12 \times 10^6$ INT instructions, $15 \times 10^6$ FP instructions, $50 \times 10^6$ L/S instructions, and $13 \times 10^6$ branch instructions. Assume the program executes on a machine with a single processor P that has a 3.2 GHz clock rate. Which of the following are correct?

（複選；至少一個正確選項，每個選項獨立計分。）

(A)
If one can optimize the program F by removing 80% of the INT instructions, the execution time of F can be reduced by more than 3%.
(B)
It is possible to make program F run 2 times faster by reducing the CPI of the FP instructions.
(C)
One can optimize program F to run more than 2 times faster by reducing the CPI of the L/S instructions to 1.2.
(D)
Suppose a new type of INT instruction called INT1 is added to the instruction set of processor P to replace the existing INT instructions. On average, through the use of the new INT instruction, we can reduce the number of INT instructions needed to execute a program by 50%, while increasing the clock cycle time by only 10%. If we replace the INT instructions in program F with the INT1 instructions, program F will run faster on processor P.
(E)
If $30 \times 10^6$ system call instructions (each has CPI of 10) are added to the program F, F will run more than 2 times slower after the addition.

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