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Electrical and Computer Engineering
CPE 431/531
Chapter 7 – Multicores,
Multiprocessors and Clusters
Dr. Rhonda Kay Gaede
UAH
Electrical and Computer Engineering
Page 2 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.1 Introduction  Motivation
•
Why multiprocessors?
•
____________________
•
____________________
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____________________
Electrical and Computer Engineering
Page 3 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.2 The Difficulty of Creating Parallel
Processing Programs
•
The difficulty with parallelism is not the
_________, it’s the ________.
•
Why is it difficult to write parallel processing
programs that are fast?
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____________
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____ ___________
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___________ ____
•
____________ _________
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________ ___
Electrical and Computer Engineering
Page 4 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.2 The Difficulty of Creating Parallel
Processing Programs  Speedup Challenge
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Suppose you want to achieve a speedup of 90 times
faster with 100 processors. What percentage of the
original computation can be sequential?
Electrical and Computer Engineering
Page 5 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.2 The Difficulty of Creating Parallel
Processing Programs  Bigger Problem
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Suppose you want to perform two sums: one is a sum of 10
scalar variables and one is a matrix sum of a pair of two
dimensional arrays, size 10 by 10. What speedup do you get
with 10 versus 100 processors
?
Electrical and Computer Engineering
Page 6 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.2 The Difficulty of Creating Parallel
Processing Programs  Bigger Problem
•
Next, calculate the speedups assuming the matrices grow to
100 by 100
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Strong scaling
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Weak scaling
Electrical and Computer Engineering
Page 7 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.2 The Difficulty of Creating Parallel
Processing Programs – Balancing Load
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To achieve the speedup of 91 on the previous larger problem
with 100 processors, we assumed the load was perfectly
balanced (each processor did 1 % of the work). Instead, show
the impact on speedup if one processor’s load is higher than al
the rest. Calculate at 2% and 5%.
Electrical and Computer Engineering
Page 8 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.3 Shared Memory Multiprocessors
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A shared memory multiprocessor (SMP) is one that offers the
programmer a _____ ________ ______ _____ across al processors
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Processor communicate through ______ __________ in memory.
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SMPs come in two flavors
– ______
– ______
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Processors need to
coordinate when sharing
data, this process is cal ed
______________,
processors must acquire a
_____
Electrical and Computer Engineering
Page 9 of 23
UAH
CPE 431/531
Chapter 7 (4
th
Ed.)
7.3 Shared Memory Multiprocessors 
Parallel Program
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Suppose we want to sum 100,000 numbers on an SMP with UMA.
Let’s assume we have 100 processors
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 Fall '09
 Staff
 CPE, UAH

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