Linus Baumberger
75 lines
2.8 KiB
Markdown
75 lines
2.8 KiB
Markdown
# Optimization: SoA (float version)
|
|
|
|
- **Author**: Linus
|
|
- **Predecessor**: variant_float_inlining.cpp
|
|
- **File(s)**: variants/variant_float_inlining_SoA.cpp
|
|
- **Status**: TBD
|
|
|
|
## What this changes
|
|
|
|
Same SoA layout switch as the double `variant_inlining_7_SoA`, but starting
|
|
from the float baseline instead of the double one. `Pedestrian` struct is
|
|
replaced by file-scope `vector<float>` arrays (`pos_x`, `pos_y`, `sb_e_x`,
|
|
`sb_e_y`, `sb_sq`, `e_x`, `e_y`, `w_x`, `w_y`, `curr_vel_x`, `curr_vel_y`,
|
|
`desired_v0`, `v_max`, `destination_x`, `destination_y`, `color`). Board
|
|
obstacles stay AoS.
|
|
|
|
Mostly a setup step for the float AVX2 variant. Same reasoning as the
|
|
double SoA: gets the j-side loads contiguous so the upcoming 8-wide AVX2
|
|
loop has clean aligned chunks.
|
|
|
|
The j loop also keeps the `r_ab_norm > EPS ? : EPS` and `two_b_sq > EPS_SQ
|
|
? : EPS_SQ` clamps from the float baseline. Float precision around close
|
|
encounters can collapse those to zero where double would not, and the clamp
|
|
keeps the division finite.
|
|
|
|
## Code (relevant snippet)
|
|
|
|
|
|
See `variants/variant_float_inlining_SoA.cpp`.
|
|
|
|
## Benchmark
|
|
|
|
Conditions: min of N runs (TBD), N_ITER=1000, -O3 -march=native -flto.
|
|
Diff is vs `variant_float_inlining`.
|
|
|
|
### x86
|
|
|
|
**Machine**: TBD
|
|
|
|
**Frequency**: TBD
|
|
|
|
| N | W(n) [Flops] | T(n) [Cycles] | Performance [Flops/Cycle] | Diff vs Predecessor |
|
|
| ---- | ------------ | ------------- | ------------------------- | ------------------- |
|
|
| 50 | | | | |
|
|
| 100 | | | | |
|
|
| 200 | | | | |
|
|
| 500 | | | | |
|
|
|
|
### ARM (Apple)
|
|
|
|
**Machine**: TBD
|
|
|
|
**Frequency**: TBD
|
|
|
|
| N | W(n) [Flops] | T(n) [Cycles] | Performance [Flops/Cycle] | Diff vs Predecessor |
|
|
| ---- | ------------ | ------------- | ------------------------- | ------------------- |
|
|
| 50 | | | | |
|
|
| 100 | | | | |
|
|
| 200 | | | | |
|
|
| 500 | | | | |
|
|
|
|
## Analysis
|
|
|
|
Layout change only, so the expectation is roughly no win on its own. The
|
|
float scalar loop already auto-vectorises in pieces with `-O3
|
|
-march=native`, so SoA doesnt buy much over what the AoS version was
|
|
already doing. The real payoff lands in the AVX2 child.
|
|
|
|
Verify passes against `baseline_float_n60_i500.csv` (from
|
|
`variant_float_baseline`) at the 1cm tolerance.
|
|
|
|
## Takeaway
|
|
|
|
Setup step for the AVX2 variant.
|