Question

Assume a program requires the execution of 50 x 106 fp instructions, 110 x 106 int instructions, 80 x 106 l/s instructions, and 16 x 106 branch instructions. The cpi for each type of instruction is 1, 1, 4, and 2, respectively. Assume that the processor has a 2 ghz clock rate. By how much must we improve the cpi of fp instructions if we want the program to run two times faster?

Answer 1

Answer :-

FP - 50 x 10^6 , CPI - 1

INT - 110 x 10^6 , CPI - 1

I/S - 80 x 10^6 , CPI - 4

Branch - 16 x 10^ 6 , CPI - 2

Clock Speed - 2 x 10^9

Time(old) = [50 x 10^6 + 110 x 10^6 + 4 x ( 80 x 10^6) + 2 x (16 x 10^ 6)] / [2 x 10^9]

Time(old) = 256 x 10^-3

Time(new) = 256 x 10^-3 /2 = 128 x 10^-3

CPI(new) x [50 x 10^6 + 110 x 10^6 + 4 x ( 80 x 10^6) + 2 x (16 x 10^ 6)] / [2 x 10^9] = 128 x 10^-3

CPI(new) = -206 / 50 = -4.12

Answer 2

Answer:

FP - 50 x 10^6 , CPI - 1

INT - 110 x 10^6 , CPI - 1

I/S - 80 x 10^6 , CPI - 4

Branch - 16 x 10^ 6 , CPI - 2

Clock Speed - 2 x 10^9

Time(old) = [50 x 10^6 + 110 x 10^6 + 4 x ( 80 x 10^6) + 2 x (16 x 10^ 6)] / [2 x 10^9]

Time(old) = 256 x 10^-3

Time(new) = 256 x 10^-3 /2 = 128 x 10^-3

CPI(new) x [50 x 10^6 + 110 x 10^6 + 4 x ( 80 x 10^6) + 2 x (16 x 10^ 6)] / [2 x 10^9] = 128 x 10^-3

CPI(new) = -206 / 50 = -4.12

Explanation:

So, we can conclude that we must improve the cpi of fp instructions at about - 4.12, if we want the program to run two times faster.