[Solved]: Amdahl's law or gustafson's law

Problem Detail: 

I am a little confused which of the two laws above i should use:

Suppose I have a computer program that can be parallelized by 70%. 30% cannot be parallelized. Every single data (100% of data) will pass the parallelizable part and also pass the non-parallelizable part.

I want to calculate how much more data i can process in a fixed amount of time if i use 2 processors instead of 1 processor.

My thinking is that since the 30% doesn't change when I increase the data, the total time spent in the non-parallelizable part will increase. Therefore, I would guess I have to use Amdahl's Law.

I think Gustafson's Law is used when the total time spent in the non-parallelizable part is constant, therefore the parallism will go up.

I cannot find a solution to this since usually Gustafson's Law is related to problems where the time is fixed and you have to find the amount of data that can be processed for given number of processors. But this case might be different?

Asked By : NoMorePen

Answered By : NoMorePen

Okay, after 4 days i finally found out and i want to share it with you: The solution is that you have to use Amdahl's Law. Iff 30% of time is sequential you should use Gustafson's Law.

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Question Source : http://cs.stackexchange.com/questions/40129