UGC NET CSE | June 2012 | Part 3 | Question: 3

Question

The concept of pipelining is a most effective in improving performance in the tasks being performed in different stages:

• A. require different amount of time
• B. require about the same amount of time
• C. require different amount of time with time difference between any two tasks being same
• D. require different amount with time difference between any two tasks being different

Answer 1

Consider 4 stages in pipeline S1,S2,S3,S4 where each stage requires 2ns

here k=no of stages=4, n is no of task =1, and tp=clock cycle time in pipeline=Max Stage Delay=2ns

Then, 1 task execution in pipeline=(k+n-1)tp=4*2=8 ns

Then, 1 task execution in non pipeline=tn=S1+S2+S3+S4=2+2+2+2=8ns

Speed Up=tn/tp=8/2=4

Efficiency=SpeedUp/No of stages in Pipeline=4/4=1 ===>100%

Now, 

Consider 4 stages in pipeline S1,S2,S3,S4 where S1=2ns,S2=8ns,S3=6ns,S4=1ns

here k=no of stages=4, n is no of task =1, and Let tp=clock cycle time in pipeline=Max Stage Delay=8ns

Then, 1 task execution in pipeline=(k+n-1)*tp=4*8=32ns

Then, 1 task execution in non pipeline=tn=S1+S2+S3+S4=2+8+6+1=17ns

Speed Up=tn/tp=17/8=2.125

Efficiency=SpeedUp/No of stages in Pipeline=2.125/4=0.53125==>53.125%

 

So, B require about the same amount of time is correct