Question

Suppose we enhance a machine to make all floating-point instructions run five times faster. If the execution time of some benchmark before the floating-point enhancement is 20 seconds, what will speedup be if half of the 20 seconds is spent executing floatingpoint instructions?

Answer 1

1.6

Step-by-step explanation:

Amdahl’s Law states: Etai = (Etabi/Ai) + Etu

Execution time after improvement -> Etai (this is what we are looking for)

Execution time affected by improvement -> Etabi = half of the 20 seg = 10 seg

Amount of improvement -> Ai = five times faster = 5

Execution time unaffected -> Etu = half of the 20 seg = 10 seg

Etai = ((10/5)+10) = 12

Speedup = 20/12 = 1.667

The program is going to be 1.667 times faster than before, this is a significant reduction in execution time. Always when you face this kind of problem, identify the variables, apply Amdahl’s Law and solve.