speedup

Question

Consider a non-pipelined processor design which has a cycle time of 10ns and average CPI of 1.4. The maximum speedup pipelined processor can get by pipelining it into 5 stages and each stage takes 2ns is______________?

 

in this question,speed up is 10/2 = 5

but why it is'nt (cycletime * cpi)/cycle time in pipeline i.e (1.4 * 10) /2 =7..

//i am just confused because speedup is (total time in non pipleine /total time in pipeline)

Answer 1

The pipelined processor you stalls which affect the CPI and new clock cycle need to be consider with the given each stage time. As that is not given you can consider  Best speed up which consider each instruction to be executed with same time as in pipeline as well as non pipeline processor.

Comments

I am not aware about the formula but that can be interpreted as 
cycletime non pipeline *cpi / cycle time in pipeline * 1 
it all depends on the questions 

This might help 
https://cseweb.ucsd.edu/classes/wi12/cse141-a/solutions/assignment5-soln.pdf

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if it is not given that it is an ideal pipeline then we can take cpi for no- pipeline..right?

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I also have the same doubt..