Optimizing Parallel Processes
Parallel Algorithms
David Mayerich
Scalable Tissue Imaging and Modeling (STIM) Laboratory
Department of Electrical and Computer Engineering
Cullen College of Engineering
University of Houston
David Mayerich
STIM Laboratory, University of Houston
Static Assignment
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Allocate work before assigning it
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Specify rules at compile-time
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Assignment remains constant
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Useful when:
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Work is predictable
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or statistically predicatable
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David Mayerich
STIM Laboratory, University of Houston
t0
t1
t2
t3
t0
t1
t2
t3
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t8
t5
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t6
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t7
t11
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t14
t15
Semi-Static Assignment
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Determine the short-term cost of work
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Assign workers based on that cost
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Barnes-Hutt Algorithm
David Mayerich
STIM Laboratory, University of Houston
Dynamic Assignment
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Prime test using trial division:
David Mayerich
STIM Laboratory, University of Houston
for(size_t i = 0; i < N; i++) {
p[i] = test_prime(x[i]);
}
// test prime using trial division
bool test_prime(int y) {
int m = sqrt(y);
for(size_t j = 2; j < m; j++) {
if(y % j == 0) return false;
}
return true;
}30
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test_prime
duration
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29
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queue
t0
t1
t2
t3
Assess Assignment Strategies
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Profile the entire program
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Calculate the overhead:
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\(T_o\) is the overhead (time spent on non-useful work)
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\(p\) is the number of processors
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\(T_p\) is the parallel runtime
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\(T_s\) is the serial runtime
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Successful strategies
David Mayerich
STIM Laboratory, University of Houston
sync()
sync()
sync()
serial
parallel
\(T_p\)
\(T_s\)