# Fast-mode CPU benchmark (2026-09-18)

Compares the default per-event phase-cache PSF splat with `--fast-mode` on a
7.4-degree 2MASS galactic-center field. Commands, raw terminal output, and
wall-clock totals are preserved below.

## Environment

- Git revision: `7ddc585` plus the uncommitted fast-mode work.
- Build: `make -j4 PSF_BACKEND=cpu SPACETIME=minkowski backend`
  (`-O2 -DNDEBUG -fopenmp`, libpng).
- Host: 12th Gen Intel Core i7-12700K, 16 hardware threads.

## Commands

All runs use the same catalog, geometry, and exposure; only the accumulation
mode changes. `--all-sky-catalog assets/2mass/processed/all_sky`,
`--width 320 --height 240 --fov-deg 10 --look-ra-deg 266 --look-dec-deg -29
--exposure 1e13 --coarse-cell-pixels 16 --refine-max-level 0`.

```sh
./build/Release/minkowski_sky --all-sky-catalog assets/2mass/processed/all_sky \
  --width 320 --height 240 --fov-deg 10 --look-ra-deg 266 --look-dec-deg -29 \
  --exposure 1e13 --coarse-cell-pixels 16 --refine-max-level 0 \
  --output /tmp/fastmode/bench/normal.png

./build/Release/minkowski_sky --all-sky-catalog assets/2mass/processed/all_sky \
  --width 320 --height 240 --fov-deg 10 --look-ra-deg 266 --look-dec-deg -29 \
  --exposure 1e13 --coarse-cell-pixels 16 --refine-max-level 0 \
  --fast-mode --fast-supersample 2 \
  --output /tmp/fastmode/bench/fast_n2.png

./build/Release/minkowski_sky --all-sky-catalog assets/2mass/processed/all_sky \
  --width 320 --height 240 --fov-deg 10 --look-ra-deg 266 --look-dec-deg -29 \
  --exposure 1e13 --coarse-cell-pixels 16 --refine-max-level 0 \
  --fast-mode --fast-supersample 4 \
  --output /tmp/fastmode/bench/fast_n4.png

./build/Release/minkowski_sky --all-sky-catalog assets/2mass/processed/all_sky \
  --width 320 --height 240 --fov-deg 10 --look-ra-deg 266 --look-dec-deg -29 \
  --exposure 1e13 --coarse-cell-pixels 16 --refine-max-level 0 \
  --fast-mode --fast-supersample 2 --fast-deposit bilinear \
  --output /tmp/fastmode/bench/fast_bil_n2.png
```

## Wall-clock totals

Measured with `date +%s.%N` around each command.

| run | wall time | images |
| --- | --- | --- |
| normal (phase cache) | 16.645 s | 5,912,840 |
| fast nearest N=2 | 1.663 s | 5,912,840 |
| fast bilinear N=2 | 1.648 s | 5,912,840 |
| fast nearest N=4 | 12.229 s | 5,912,840 |

Fast nearest N=2 is about 10x faster than the phase-cache path on this
PSF-dominated field. N=4 increases the supersampled buffer and kernel area by
4x each and becomes convolution-bound.

## Raw terminal output

```text
===== normal.log =====
Blackbody LUT: 1024 CIE 1931 2-deg 1 nm-linear XYZ nodes, T=[670.146556, 101408.88] K, loaded assets/blackbody/cie1931_2deg_xyz_1024.grbblut in 0.000056 s; payload fnv1a64=0e39867b0e70a809
Blackbody backend: lut
PSF cache ready: 64x64 phases, radius 47 px, relative tail 1e-08, tail abs 1e-06, boundary 1e-07, build 0.725 s
Catalog prefetch: 96 requested, 96 newly loaded (6618807 stars), 0 unavailable in 0.696 s; 4 loader workers
Rendered 5912840 images from 6618807 catalog stars to /tmp/fastmode/bench/normal.png (ok)
PSF splats: cached 5912840, cached wing-clipped 0, direct fallbacks 0, discarded below min-Y 0
===== fast_n2.log =====
Fast mode is a preview approximation; --max-cache-psf-flux is ignored and one global kernel is used for every event.
Blackbody LUT: 1024 CIE 1931 2-deg 1 nm-linear XYZ nodes, T=[670.146556, 101408.88] K, loaded assets/blackbody/cie1931_2deg_xyz_1024.grbblut in 0.000045 s; payload fnv1a64=0e39867b0e70a809
Blackbody backend: lut
Fast PSF: supersample 2x, deposit nearest, kernel radius 93 ss px (46.50 final px), retained flux 1.000000, cached 4-point quadrature
Catalog prefetch: 96 requested, 96 newly loaded (6618807 stars), 0 unavailable in 0.708 s; 4 loader workers
Rendered 5912840 images from 6618807 catalog stars to /tmp/fastmode/bench/fast_n2.png (ok)
Fast PSF splats: deposited 5912840, wing-clipped 0, discarded below min-Y 0
===== fast_n4.log =====
Fast mode is a preview approximation; --max-cache-psf-flux is ignored and one global kernel is used for every event.
Blackbody LUT: 1024 CIE 1931 2-deg 1 nm-linear XYZ nodes, T=[670.146556, 101408.88] K, loaded assets/blackbody/cie1931_2deg_xyz_1024.grbblut in 0.000058 s; payload fnv1a64=0e39867b0e70a809
Blackbody backend: lut
Fast PSF: supersample 4x, deposit nearest, kernel radius 185 ss px (46.25 final px), retained flux 1.000000, cached 4-point quadrature
Catalog prefetch: 96 requested, 96 newly loaded (6618807 stars), 0 unavailable in 0.709 s; 4 loader workers
Rendered 5912840 images from 6618807 catalog stars to /tmp/fastmode/bench/fast_n4.png (ok)
Fast PSF splats: deposited 5912840, wing-clipped 0, discarded below min-Y 0
===== fast_bil_n2.log =====
Fast mode is a preview approximation; --max-cache-psf-flux is ignored and one global kernel is used for every event.
Blackbody LUT: 1024 CIE 1931 2-deg 1 nm-linear XYZ nodes, T=[670.146556, 101408.88] K, loaded assets/blackbody/cie1931_2deg_xyz_1024.grbblut in 0.000047 s; payload fnv1a64=0e39867b0e70a809
Blackbody backend: lut
Fast PSF: supersample 2x, deposit bilinear, kernel radius 93 ss px (46.50 final px), retained flux 1.000000, cached 4-point quadrature
Catalog prefetch: 96 requested, 96 newly loaded (6618807 stars), 0 unavailable in 0.712 s; 4 loader workers
Rendered 5912840 images from 6618807 catalog stars to /tmp/fastmode/bench/fast_bil_n2.png (ok)
Fast PSF splats: deposited 5912840, wing-clipped 0, discarded below min-Y 0
```

## Tone-mapped difference vs the normal render

```text
fast_n2     mean=1.1213 rms=1.7255 max=14 px>16=0/76800
fast_n4     mean=0.5516 rms=0.9146 max=8 px>16=0/76800
fast_bil_n2 mean=0.2091 rms=0.4793 max=16 px>16=0/76800
```

`mean`/`rms` are per-channel 8-bit differences; `px>16` counts pixels with any
channel more than 16 levels from the normal render. No pixel exceeds 16 in any
run. These are display-scale differences from the measured deposition tradeoff;
they are not a bit-exact regression baseline.