Any function requires three stages to complete Fetch Decode

Any function requires three stages to complete: Fetch, Decode and Execute. For the purpose of this question we will assume that each of these stages take t ms to complete. Assume a Function Turbo runs 3 times in a loop. How long will it take for the loop to complete assuming that there is no pipeline and only one stage (Fetch, Decode, or Execute) can run at a given time on your microprocessor? How long will it take for the loop to complete assuming that there is a three stage pipeline? Was there an advantage of using a pipeline? Give your answer in terms of percentage improvement. Give your answers in terms of t for each of the question above. You must clearly state any assumption necessary for your solution.

Solution

Fetch takes = t ms

Decode takes = t ms

Execute takes = t ms

a.

No pipeline

one function run takes = t ms + tms + t ms = 3 t ms.

If function executes 3 times in the loop total time taken = 3*(3 t ms) = 9 t ms.

b.

using 3 stage Pipeline

t ms                  t ms                    tms                       t ms                           t ms

Time taken for the loop = t ms + t ms + t ms + t ms + t ms = 5t ms

c.

So there is advantage of using pipeline(5t ms) as compared to no pipeline(9t ms)

% improvement = (9-5)/9 *100 = 44.4 %

Fetch	Decode	Execute
	Fetch	Decode	Execute
		Fetch	Decode	Execute