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cop5615fa10quiz4Key

# cop5615fa10quiz4Key - used 2(a Low priority task L runs...

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Quiz 4 Key COP 5615 Fall 2010 Put your last name in the top right corner of your answer sheet, with your first name below it. Answer both questions, indicating the question number and part you are answering. 1. What is the maximum speedup possible according to Amdahl's Law for a program that is 25% inherently serial and 75% parallelizable using N processors for the values of N below? Show your work. (a) N=3 processors. (b) N=6 processors. (c) What is the maximum speedup possible? 2. Give a simple example of (a) Pass-through blocking. (b) Priority inversion. Explain your examples. KEY 1. Amdahl's Law states that the maximum speedup for a program with fraction P parallelizable and (1-P) inherently serial, using N processors is S_max = 1/[(1-P) + P/N]. (a) N=3 so S_max = 1/[.25 + .75/3] = 2 (b) N=6 so S_max = 1/[.25 + .75/6] = 2.67 (c) The maximum speedup is 1/[.25+0] = 4, no matter how many processors are
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