A diagnostic stack-sampling profiler, off by default. A sampler thread captures the stacks of
registered generation workers with FPlatformStackWalk::CaptureThreadStackBackTrace every N us and
tags each sample with the tile's LOD. Symbolisation (inline frames included) happens after the
run, into a bounded CSV plus a summary. Registration is per tile task, never per sample; when the
sampler is off it costs one relaxed atomic load. Game: -voxel.SampleStacks=<us>. Commandlet:
-samplestacks[=us]. The streaming latency line now also prints applied tile, visible tile and
triangle counts.
Instrument checks (Codex, PERF-SAMPLED.md):
- a planted 20 ms busy loop was found at 10.5% inclusive, the expected share, then removed
- closure: 193k static / 251k moving samples, 0 capture failures, <0.75% wait frames,
leaf resolved for 82-84%
- static game output identical with the sampler on or off: 841 tiles, 447 visible, 669,834
triangles
- overhead at 1 ms: +4.7% static worker CPU; moving worker CPU within noise, moving timing +4-5%.
So trust large shares, not single-digit deltas.
The finding, on the game path (the owner's instruction: profile the game, not the export):
all-LOD inclusive static moving
BuildChunkCache 79.5% 80.5%
VF_FindPlayerFitPointForRoom 73.4% 74.0%
About three quarters of in-game worker CPU goes to player-fit searches for rooms. They are
recomputed on every per-worker room-cache rebuild, and coarse tiles span many cache windows. At
LOD0 the costs are the cave warp (3 Perlin per sample), the swept tunnel evaluated both in the
SDF and in EvaluateTunnelCoreWorld (~12% inclusive each, duplication confirmed), and the passage
structural tail (~11-14%). Candidate AABB rejection is cheap (1.5-2.2%). The 74-field params copy
does not show up as a separate cost.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VZS94UH8bSsBeg5sZaxe2Y
