. Computing the overall effective CPI is done by looking at the different types
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Question
. Computing the overall effective CPI is done by looking at the different types of instructions and their individual cycle counts and averaging. Please use the information in the table to answer the following questions: Operation Frequency CPl ALU 50% Load 20% Store 10% Branch 0% Answer the following questions 1. What is the overall effective CPI of the machine according to the table? 2. What is the overall effective CPl of the machine if a better data cache reduces the average load time from 5 to 2 cycles?Explanation / Answer
1. CPI (Cycles per Instruction) = Total program execution cycles/Total instruction executed
Given above the total number of instructions executed = 100. (since frequency of instructions are given in percentage)
CPI = (50/100 * 1)+ (20/100 *5) + (10/100 * 3) + (20/100 * 2)
= (50 + 100 + 30 + 40)/100
= 220/100 = 2.2
Overall effective CPI of the machine = 2.2
2.
If the average load time is reduced from 5 to 2 cycles, then
CPI = (50/100 * 1) + (20/100 * 2) + (10/100 * 3) + (20/100 * 2)
= (50 + 40 + 30 + 40)/100
= 160/100 = 1.6
The overall effective CPI of the machine if a better data cache reduces the average load time from 5 to 2 cycles = 1.6
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