Question

Another pitfall cited in Section 1.10 is expecting to improve the overall performance of a computer by improving only one aspect of the computer. This might be true, but not always. Consider a computer running programs with CPU times shown in the following table. FP Instr L/S Instr. Branch Instr. Total Time 85 s 93 s 28 s 310s 1.13.1 [5] <110> How much is the total time reduced if the time for FP opera tions is reduced by 30 %? 1.13.2 [5] <1.10> How much is the time for INT operations reduced if the total time is reduced by 18 %? 1.13.3 [5] < 1.10 > Can the total time can be reduced by 25 % by reducing only the time for branch instructions?

Answer 1

1.13.1

fp operation time = 85sec

reduced fp operation time = 30 %

so new fp operation time = 85 - 0.3 * 85 = 59.5

so now total time = 310 + 59.5 - 85 = 284.5

so percentage reduction = 8.2%

1.13.2

INT instruction current execution time is = 310 - 93 - 85 - 28 = 104

new total time = 310 - 0.18 * 310 = 254.2

so new int time = 254.2 - 93 - 85 -28 = 48.2

so time of int operation reduced = 104 - 48.2 = 55.8

1.13.2

total time reduced = 25 %

so new total time = 310 - 0.25 * 310 = 232.5

so time for branch = 232.5 - 93 - 85 - 104 = -49.5

so this says that new branch instruction time = -49.5 which is not possible

so answer is no It cannot be done only by reducing branch instruction time

Answer 2

iven: Let Floating Point to FP and the execution time of the FP = 70s The total time of the CPU = 250s Execution time of the Branch instruction = 40s Execution time of the L/S instruction = 85s Then, we have to decrease the FP instruction time.             Then, we have to find the total time required to run the program.                             Finally, the percentage of the decreased total time.                                            

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