ch6a_Pipeline - CS 250 Fall 2002 CS 250 Fall 2002 Question...

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Unformatted text preview: CS 250 Fall 2002 CS 250 Fall 2002 Question A professor is about to grade the exam of CS 250. 5 questions in the exam and 50 students in the class The professor has 5 TAs. How should the professor plan the grading? Goal: To minimize the overall grading time What if each TA can only grade one question? CS 250 Fall 2002 CS 250 Fall 2002 Dumb Approach Grade sequentially TA1 TA2 TA3 TA4 TA5 Q 1 Q 2 Q 3 Q 4 Q 5 Pp#1 Pp#2 Q 2 Q 1 Q 3 Q 4 Q 5 Q 2 Q 1 Q 3 Q 4 Pp#3 Q 5 CS 250 Fall 2002 CS 250 Fall 2002 Dumb Approach Performance = 50 (papers) * 5 (questions) * unit time = 250 unit times CS 250 Fall 2002 CS 250 Fall 2002 Smart Approach Pipelining the grading process TA1 TA2 TA3 TA4 TA5 Q 1 Q 2 Q 3 Q 4 Q 5 Pp#1 Pp#2 Q 2 Q 1 Q 3 Q 4 Q 5 Q 2 Q 1 Q 3 Q 4 Pp#3 startup time = 4 CS 250 Fall 2002 CS 250 Fall 2002 Smart Approach Performance = 4 (startup time) + 50 (papers) = (5 1) + 50 = (# questions 1) + (# of papers) = 54 unit times Speedup = 250 / 54 & 5.0, (not 5.0 because of startup time) But, well get 5.0 when # of papers is very large CS 250 Fall 2002 CS 250 Fall 2002 Chapter 6: Pipelining Why pipelining? Performance improvement How? Using the example, each TA & each execution step The factor of improvement (speedup) Ideally, W (# of steps) In practice, smaller than (# of steps) Smaller by how much? Why smaller? CS 250 Fall 2002 CS 250 Fall 2002 Why Smaller? Execution stop to wait for data or control being produced Data dependence lw $1 , 200($2) add $3, $4, $1 Control dependence bne $1, $2, target add $3, $4, $5 CS 250 Fall 2002 CS 250 Fall 2002 Outline...
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ch6a_Pipeline - CS 250 Fall 2002 CS 250 Fall 2002 Question...

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