How do we know which instruction to choose for question B and C? questIon Consid

Question

How do we know which instruction to choose for question B and C?

questIon Consider the following instruction set characteristics Percentage 20% 30% 5% 20% 25% Instruction Type CPI 4 a) What is the average CPI? b) In order to improve the performance, you can change one type of instructions to have a CPI of 1, which one do you choose to maximize the improvement, and what is the new CPI? c) What if changing the CPI of one type to 1 will increase the maximum CPI of the remaining instructions by 1, which one do you choose to set to 1?

Explanation / Answer

a) Average CPI = (5x20 + 3x30 + 6x5 + 4x20 + 3x25)/100 = 3.75

b) Select the instruction which is the highest contributor i.e. whose multiplication of CPI of the instruction and percentage is the highest, hence instruction A having the highest value of multiplication i.e. 5x20 should be selected to improve and maximize the performance.

The new CPI = (1x20 + 3x30 + 6x5 + 4x20 + 3x25)/100 = 2.95

c) To get the highest CPI and selecting the instruction with the new CPI of 1, select the one with the lowest contribution which is instruction C having a contribution of 30%.

The new CPI = (5x20 + 3x30 + 1x5 + 4x20 + 3x25)/100 = 3.5

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