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Loop Optimizations
Amdahl’s Law
- Determines speed up
- α: fraction of code is scalar
- 1-α: fraction of code which is parallelizable
- 1 operation per unit time is scalar unit
- ζoperations per unit time in parallel units
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- where 0 ≤ α≤ 1, and ζ≥1
α
0
0.1
0.25
0.5
1 |
ζ=10
10
5.26
3.08
1.82
1 |
ζ=20
20
6.9
3.48
1.90
1 |
- To achieve any significant speedup, parallel code must be greater then 90%
- Most of the execution time is spent in small sections of code. So concentrate on critical sections (loops)
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Loop parallelization is beneficial
- Inner most loop parallelization is the most beneficial
- Sscalar component of the code is the limiting factor
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