HIP: record direct atomic PSF timings
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# HIP direct-atomic 高密度 PSF endpoint（2026-09-05）
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## 目的和边界
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测量 production HIP `PsfEventSink` 在一个高表面密度 2MASS tile 上的端到端表现，并将 GPU
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传输、kernel 与 HDR 下载分开记录。此记录验证 direct-global-atomic 的实际成本边界；它不是
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tile-local reduction 的性能声明，也不把 kernel 时间直接归因为 atomic contention。
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## 控制条件
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- Source baseline: `7a80086f63e8b1e5f27d9524ba0455f2d6e49be5`
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(`Feat: add initial HIP PSF backend`)；HIP timing counters 是该基线之上的未提交诊断改动，
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不改变 event、HDR 或输出路径。
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- Host: i7-12700K；`OMP_NUM_THREADS=16`。
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- GPU: AMD Radeon RX 9070 (`gfx1201`), 56 CUs, 15.9 GiB global memory；HIP runtime 是主机
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实际 probe 所报告的设备。
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- Build: Release；C11/`-march=native -O2 -pipe`、OpenMP、PNG；HIP 后端由
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`PSF_BACKEND=hip` 选择。
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- Input: `assets/2mass/processed/all_sky/tile_ra252_dec048.csv`，54,160 stars。
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- Camera: Minkowski；RA 252.5 deg、Dec -41.5 deg、FOV 0.6 deg、1920 x 1920 px、
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`--coarse-cell-pixels 240`（128 triangles / 81 initial rays）。
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- PSF: FWHM 2.7 px、Moffat beta 3、exposure `1e15`、
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`--max-cache-psf-flux 1e300`。cache radius 266 px；本次没有 min-Y discard 或 direct fallback。
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这里刻意以较大的 coarse cell 减少 triangle 枚举工作，使固定 catalog 与相同镜头映射下的
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splat 阶段成为可比较对象；它不是全天空或生产 4K 吞吐量估计。
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## 命令与原始输出
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CPU reference（同一输入与参数；在 HIP 命令确认退出后顺序运行）：
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```console
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export OMP_NUM_THREADS=16
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time build/Release/minkowski_sky \
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--catalog assets/2mass/processed/all_sky/tile_ra252_dec048.csv \
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--look-ra-deg 252.5 --look-dec-deg -41.5 --fov-deg 0.6 \
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--width 1920 --height 1920 --coarse-cell-pixels 240 \
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--exposure 1e15 --psf-fwhm-pixels 2.7 --psf-moffat-beta 3 \
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--max-cache-psf-flux 1e300 --output /tmp/cpu_psf_dense.png --verbose
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PSF cache ready: 64x64 phases, radius 266 px, relative tail 1e-08, tail abs 1e-06, boundary 1e-07, build 20.738 s
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Frame 0: tracing 81 initial rays from 128 mesh triangles...
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Frame 0: initial ray trace finished in 0.009 s.
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Frame 0: traced 81 lens vertices; starting catalog render.
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Frame 0: finding and prefetching catalog tiles...
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Frame 0: catalog prefetch finished (0 candidate tiles).
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Frame 0: splatting 128 lens triangles...
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Frame 0: splat worker 14/16 started.
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Frame 0: splat worker 10/16 started.
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Frame 0: splat worker 16/16 started.
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Frame 0: splat worker 1/16 started.
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Frame 0: splat worker 12/16 started.
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Frame 0: splat worker 13/16 started.
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Frame 0: splat worker 5/16 started.
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Frame 0: splat worker 11/16 started.
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Frame 0: splat worker 7/16 started.
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Frame 0: splat worker 6/16 started.
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Frame 0: splat worker 3/16 started.
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Frame 0: splat worker 4/16 started.
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Frame 0: splat worker 2/16 started.
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Frame 0: splat worker 9/16 started.
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Frame 0: splat worker 8/16 started.
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Frame 0: splat worker 15/16 started.
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Frame 0: splat worker 14/16 reached 8 local triangles.
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Frame 0: splat worker 2/16 reached 8 local triangles.
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Frame 0: splat worker 10/16 reached 8 local triangles.
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Frame 0: splat worker 7/16 reached 8 local triangles.
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Frame 0: splat worker 1/16 reached 8 local triangles.
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Frame 0: splat worker 11/16 reached 8 local triangles.
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Frame 0: splat worker 3/16 reached 8 local triangles.
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Frame 0: splat worker 5/16 reached 8 local triangles.
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Frame 0: splat worker 4/16 reached 8 local triangles.
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Frame 0: splat worker 12/16 reached 8 local triangles.
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Frame 0: splat worker 16/16 reached 8 local triangles.
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Frame 0: splat worker 13/16 reached 8 local triangles.
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Frame 0: splat worker 9/16 finished after 4 local triangles.
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Frame 0: splat worker 6/16 finished after 5 local triangles.
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Frame 0: splat worker 15/16 finished after 5 local triangles.
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Frame 0: splat worker 8/16 finished after 5 local triangles.
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Frame 0: splat worker 11/16 finished after 9 local triangles.
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Frame 0: splat worker 1/16 finished after 9 local triangles.
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Frame 0: splat worker 5/16 finished after 9 local triangles.
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Frame 0: splat worker 7/16 finished after 9 local triangles.
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Frame 0: splat worker 10/16 finished after 9 local triangles.
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Frame 0: splat worker 16/16 finished after 8 local triangles.
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Frame 0: splat worker 13/16 finished after 8 local triangles.
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Frame 0: splat worker 4/16 finished after 8 local triangles.
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Frame 0: splat worker 3/16 finished after 9 local triangles.
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Frame 0: splat worker 12/16 finished after 8 local triangles.
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Frame 0: splat worker 2/16 finished after 10 local triangles.
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Frame 0: splat worker 14/16 finished after 13 local triangles.
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Frame 0: catalog splatting finished in 7.1 s; writing image...
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Rendered 26172 images from 54160 catalog stars to /tmp/cpu_psf_dense.png (ok)
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PSF splats: cached 26172, cached wing-clipped 0, direct fallbacks 0, discarded below min-Y 0
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build/Release/minkowski_sky --catalog --look-ra-deg 252.5 --look-dec-deg 418.79s user 3.19s system 1472% cpu 28.654 total
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```
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HIP measurement（加入 timing counters 后；其余参数相同）：
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```console
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make -B PSF_BACKEND=hip SPACETIME=minkowski backend
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export OMP_NUM_THREADS=16
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time build/Release/minkowski_sky_hip \
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--catalog assets/2mass/processed/all_sky/tile_ra252_dec048.csv \
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--look-ra-deg 252.5 --look-dec-deg -41.5 --fov-deg 0.6 \
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--width 1920 --height 1920 --coarse-cell-pixels 240 \
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--exposure 1e15 --psf-fwhm-pixels 2.7 --psf-moffat-beta 3 \
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--max-cache-psf-flux 1e300 --output /tmp/hip_psf_dense_timing.png --verbose
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PSF cache ready: 64x64 phases, radius 266 px, relative tail 1e-08, tail abs 1e-06, boundary 1e-07, build 20.915 s
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Frame 0: tracing 81 initial rays from 128 mesh triangles...
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Frame 0: initial ray trace finished in 0.008 s.
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Frame 0: traced 81 lens vertices; starting catalog render.
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Frame 0: finding and prefetching catalog tiles...
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Frame 0: catalog prefetch finished (0 candidate tiles).
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Frame 0: splatting 128 lens triangles...
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Frame 0: catalog splatting finished in 3.2 s; writing image...
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Rendered 26172 images from 54160 catalog stars to /tmp/hip_psf_dense_timing.png (ok)
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PSF splats: cached 26172, cached wing-clipped 0, direct fallbacks 0, discarded below min-Y 0
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HIP PSF: 26172 events in 2 batches (2 timed); upload 0.000073 s, kernel 2.950377 s, download 0.011256 s
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build/Release/minkowski_sky_hip --catalog --look-ra-deg 252.5 --look-dec-deg 326.85s user 1.53s system 1314% cpu 24.985 total
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```
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两次命令都没有设置 `TIMEFMT`；末行是 zsh 默认 `%J %U user %S system %P cpu %*E total`
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格式的原始输出。它们按顺序运行：先确认没有 renderer benchmark，再执行 HIP，确认其退出后才
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执行 CPU，期间没有第二个 renderer benchmark。
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`cmp` 比较 `/tmp/cpu_psf_dense.png` 与 `/tmp/hip_psf_dense_timing.png`：`PNG byte comparison:
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identical`。
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## 结果和决策
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CPU catalog splatting 为 7.1 s，HIP 为 3.2 s（约 2.22x）；完整进程的 zsh elapsed time 为
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28.654 s（CPU）与 24.985 s（HIP）。在 HIP 的 3.2 s 中，两个 batch 的 kernel event 合计
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2.950377 s；上传为 0.000073 s、最终 HDR 下载为 0.011256 s。因此这个 endpoint 的 GPU 端
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时间由 kernel 主导，而不是 PCIe。
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但 kernel 还包括每个 event 的圆形 PSF 支持域遍历、cache 权重读取和 HDR atomic 写入。这里只有
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一个密度／支持域组合，也没有关闭或替代 atomic 的对照，所以不能以此声称 global atomics 的热点
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竞争是主导瓶颈。结论是保留 direct atomic，并先测密度与支持域扫描；暂不引入 tile-local reduction
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或其分桶／重排复杂度。
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