Recall Amdahls Law if application is 80 parallelaffected and

Recall Amdahl\'s Law, if application is 80% parallel(affected) and 20% serial(unaffected), what is the speedup if moving from 1 core computer to 2 cores computer? What about moving from 1 core to 4 cores? What about moving from 1 core to +infinity cores?

Solution

Amdahls law implies that

Speedup = 1/[(1-F)+F/N]

F = Fraction of enhanced application(Parallel)

N = Number of core

1. Moving from 1 core computer to 2 core computer

S1 = 1/(.2+.8/1) = 1

S2 = 1/(0.2 + 0.8/2) = 1.66

So moving from one core computer to 2 core computer you will get 1.66 times speedup over one core computer.

2. Moving from 1 core computer to 4 core

S4 = 1/(0.2+0.8/4)= 2.5

you will gain 2.5 times speedup than 1 core computer.

3. moving from one core to infinite

Sinf = 1/(0.2 + 0.8/infinite) = 1/0.2=5

5 times speedup than 1 core computer.