The table below shows the execution time in percentage for various sections of a

Question

The table below shows the execution time in percentage for various sections of a code. Answer the following questions clearly showing all your steps. a. Define Amdahl's law. b. Which section takes the least execution time and which section takes the most execution time? c. By reducing the execution time of the write back section, can the entire code gain a speed-up of 2? d. By reducing the execution time of the computation section, can the entire code gain a speed-up of 3? e. Which of the two sections' execution time can be reduced so that the entire code can gain a speed-up of 4?

Explanation / Answer

a) Amdahl's Law is a formula which gives the theoretical speedup in latency of the execution of a task at fixed workload that can be expected of a system whose resources are improved. Generally the resorces which are used more are improved.

b) Final Section takes least execution time and Computation section takes most execution time.

c) Soverall = 1/( (1-F) + F/S ) where F is the fraction enhance and S is orignal speed up

Soverall= 1 / (1-0.15 +0.15/S)

=1 / (0.85 + 0.15/S)

= S /( 0.85S +0.15)

So Speed up < 2

d) Soverall= 1 / (1-0.7 +0.7/S)

= S /( 0.3S + 0.7)

Hence Speed up is greater than 3

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