#pipeline #self doubt

Question

Consider a 5—stage pipeline processor used to execute 200 number of instructions and among those 100 instructions cause 3 stall cycles each. What is the total cycles required for these operation if CPI is not equal to one.

Comments

$(200+5-1) + (3*100) = 504$.

You can also try this by table filling

 

1

2

3

4

5

6

7

….

100

101

102

103

104

105

106

107

108

109

110

111

112

…..

500

501

502

503

504

I1

F

D

E

M

W

I2

F

D

E

M

W

I3

F

D

E

M

W

.

.

I100

F

D

E

M

W

I101

$\phi$

$\phi$

$\phi$

F

D

E

M

W

I102

$\phi$

$\phi$

$\phi$

F

D

E

M

W

.

$\phi$

$\phi$

$\phi$

I200

F

D

E

M

W

100 instructions with no stalls :

$5 + (100-1)* 1 = 104$ cycles

Next 100 with 3 stall cycles :

$108 + (100-1)*4  = 504$ cycles