Question

What could be the speedup factor for a program if parallel part was %50 and the serial part was %50 as well for the following number of threads: 2, 4 and 8.

Answer 1

Q-> What could be the speedup factor for a program if parallel part was %50 and the serial part was %50 as well for the following number of threads: 2, 4 and 8.

Given:

p = fraction of parallel part of the program = 50% = 0.5

.

let t = no of threads

i) t = 2

speedup = 1 / ( (1-p) + p/t )

=> speedup = 1 / ( 0.5 + 0.5 / 2) = 1.33

.

ii) t = 4

speedup = 1 / ( (1-p) + p/t )

=> speedup = 1 / ( 0.5 + 0.5 / 4) = 1.6

.

iii) t = 8

speedup = 1 / ( (1-p) + p/t )

=> speedup = 1 / ( 0.5 + 0.5 / 8) = 1.77

.

=>

for 2 threads, speedup will be 1.3

for 4 threads, speedup will be 1.6

for 8 threads, speedup will be 1.7