Perf: RT build costs ~3 ms CPU per frame with ray-traced shadows on #93
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sky_line/Slipstream#93
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With ray-traced projector shadows on (RenderVKProjectorShadows=2), the CPU-side RT build costs 2.8-3.6 ms/frame (section
vk_rtBuild) - more than the GPU work it feeds. The frame was CPU-bound (~14 ms CPU vs ~8 ms GPU, 5090, busy sim).Look at: per-frame BLAS/TLAS bookkeeping on the CPU (slot scans, build-list assembly, rigged refit lists, descriptor writes - ~21 set writes/frame by design), whether static BLAS state can be cached and only diffs processed, and moving instance/TLAS input generation fully to the existing compute pass. Target: <0.5 ms CPU when nothing changed.
Current numbers (2026-09-30,
4d377811f1): RT build CPU = 0.33 ms/frame (vk_rtBuild) with ray-traced sun + 10 RT projectors; GPU side c_tlas 0.74 ms, c_blas_refit 0.35 ms. Closing; RT cost is now GPU tracing in pass 1, tracked in #195.