UGC NET CSE | December 2012 | Part 3 | Question: 49

Question

Let $f$ be the fraction of the computation (in terms of time) that is parallelizabl$e$. $P$ the number of processors in the system, and $s_p$ the speed up achievable in comparison with sequential  execution – then the $s_p$ can be calculated using the relation:

• A. $\frac{1}{1-f-f/P}$
• B. $\frac{P}{P-f(P+1)}$
• C. $\frac{1}{1-f+f/P}$
• D. $\frac{P}{P+f(P-1)}$

Answer 1

answer C

• Let execution time without parallelism is 1.
• If f is the fraction of parallel computation (1-f) time must be spend for sequential computation.
• f fraction of computation can be distributed among P processors; So it will take f/P time to complete computation.
• Total time for computation with parallelism = 1-f + f/P

speed up = time _{without parallelism} / time _{with parallelism}

= 1/ 1-f + f/P

// Correct me if I am wrong!

Comments

@Shiva,what basis you've used for calculation?