Linus Baumberger
71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
# Optimization: Struct of Arrays (SoA)
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- **Author**: Linus
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- **Predecessor**: variant_inlining_7.cpp
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- **File(s)**: variants/variant_inlining_7_SoA.cpp
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- **Status**: TBD
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## What this changes
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Replaced the `Pedestrian` struct with parallel `vector<double>` arrays, one
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per field (`pos_x`, `pos_y`, `e_x`, `e_y`, `sb_e_x`, `sb_e_y`, `sb_sq`, ...).
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Board obstacles are left as AoS since there are only a handful of them.
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Mostly a setup step for AVX2: with SoA the inner ped-ped loop reads
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contiguous chunks of `pos_x[j..]`, which is what we'll want for aligned
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vector loads.
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## Code (relevant snippet)
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```cpp
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vector<double> pos_x, pos_y;
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vector<double> sb_sq, sb_e_x, sb_e_y;
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vector<double> e_x, e_y;
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vector<double> curr_vel_x, curr_vel_y;
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// ...
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```
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See `variants/variant_inlining_7_SoA.cpp`.
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## Benchmark
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Conditions: 2 runs, N_ITER=1000, -O3 -march=native -flto. Diff is vs
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`variant_inlining_7`.
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On my local machine i had an improvement of about 10-15% for low N and about 5% speed up for higher N
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### x86
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**Machine**: TBD
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**Frequency**: TBD
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| N | W(n) [Flops] | T(n) [Cycles] | Performance [Flops/Cycle] | Diff vs Predecessor |
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| ---- | ------------ | ------------- | ------------------------- | ------------------- |
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| 50 | | | | |
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| 100 | | | | |
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| 200 | | | | |
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| 500 | | | | |
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| 1000 | | | | |
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### ARM (Apple)
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**Machine**: TBD
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**Frequency**: TBD
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| N | W(n) [Flops] | T(n) [Cycles] | Performance [Flops/Cycle] | Diff vs Predecessor |
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| ---- | ------------ | ------------- | ------------------------- | ------------------- |
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| 50 | | | | |
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| 100 | | | | |
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| 200 | | | | |
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| 500 | | | | |
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| 1000 | | | | |
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## Analysis
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No in depth Analysis done, just thought i wanna share it so you can also use it for further optimizations
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## Takeaway
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Layout change, not a performance win by itself. Sets up the AVX2 variant.
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