UGC NET CSE | June 2012 | Part 3 | Question: 5

Question

Suppose that the given application is run on a 64-processor machine and that 70 percent of the application can be parallelized. Then the expected performance improvement using Amdahl’s law is

• A. 4.22
• B. 3.22
• C. 3.32
• D. 3.52

Comments

Answer is b?

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yes it is b

Answer 1

According to Amdahl's law, in case of parallelization,if P is the proportion of the program that can be made parallel, then (1-P) is the proportion that cannot be parallelized. Then the maximum speedup that can be achieved by using N processor is, S(N)=1/(1-P)+P/N where N refers to the no of processors, and P refers to the proportion that can be parallelized.
In the question above, no of processor, N=64
The proportion of the program that can be made parallel, P = 70%=0.7
So, substituting in the formula, we get, 1/(1-0.7)+0.7/64=1/0.3+0.0109375=1.0.310975
=3.215
=3.22
Therefore, the option is B.

Comments

Hi
   Could anyone explain about "1.0.310975" !!! When I tried solving the equation I got 3.34427...!! The options have minute differences.
Regards

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1-0.7=0.3 and

0.7/64 = 0.0109  so their sum=0.3109

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@Sanjay Sharma Sir, Sir 1/0.3 is 3.333 and then adding something to it cannot give lesser value!!!!

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@Girjesh Chouhan I think you are taking formula wrong, it is 1 / ((1-p) + (p/n))

Answer 2

S(N)=1/[(1-P)+(P/N)] where N refers to the number of processors = 64.

S(N) = 1/[(1-0.7)+(0.7/64)=1/[(0.3)+0.0109375] = 1/0.3109375 = 3.2160804020100502512562814070352=3.22

So option (B) is the right Answer.