The instruction mix for a machine M1 is shown in the followingtable: Instruction
ID: 3610960 • Letter: T
Question
The instruction mix for a machine M1 is shown in the followingtable:
Instruction Class
Frequency
Cycles
load
20%
3
store
20%
3
ALU op
40%
1
branch
10%
2
As a designer you consider an alternative implementation M2, byadding a new instruction that
could have up to three memory operands. The CPI for this newinstruction is 4, and its
implementation would increase the clock cycle period by a factorof 1.5. However, the new
instruction would effectively replace half of the loadinstructions and half of the store
instructions.
a. What is the average CPI for M1?
(.2)* 3 = .6
(.2)* 3 = .6
(.4)* 1 = .4
(.1)* 2 = .2
Total CPI for M1 = 1.8/.9 = 2
b. What is the average CPI for M2 if the frequency of newinstruction is 10%?
Instruction Class
Frequency
Cycles
load
20%
3
store
20%
3
ALU op
40%
1
branch
10%
2
Explanation / Answer
Instruction Class
Frequency
Cycles
load
20%
3
store
20%
3
ALU op
40%
1
branch
10%
2
New instruction
10%
6(4*1.5)
(.2)* 3 = .6
(.4)* 1 = .4
Instruction Class
Frequency
Cycles
load
20%
3
store
20%
3
ALU op
40%
1
branch
10%
2
New instruction
10%
6(4*1.5)
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