A particular parallel program computation requires 100 seconds when executed…
2013
A particular parallel program computation requires 100 seconds when executed on a single CPU. If 20% of this computation is strictly sequential, then theoretically the best possible elapsed times for this program running on 2 CPUs and 4 CPUs respectively are
- A.
55 and 45 seconds
- B.
80 and 20 seconds
- C.
75 and 25 seconds
- D.
60 and 40 seconds
Attempted by 10 students.
Show answer & explanation
Correct answer: D
According to Amdahl's Law, execution time T_N = S + P/N. Given 100s total with 20% sequential, S = 20s and P = 80s.
For 2 CPUs: T_2 = 20 + 80/2 = 60s.
For 4 CPUs: T_4 = 20 + 80/4 = 40s.