From b34c1f34b067aa7baa446e09842a613374299afa Mon Sep 17 00:00:00 2001 From: Ralph Kuepper Date: Thu, 16 Jul 2026 13:31:51 +0200 Subject: [PATCH] docs: HW-vs-SW Lumen measured - HW costs +20 ms/frame on the 760M (EN-023/EN-058c answered) --- docs/tickets.md | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/docs/tickets.md b/docs/tickets.md index 157b5732..08118d25 100644 --- a/docs/tickets.md +++ b/docs/tickets.md @@ -1763,6 +1763,34 @@ behave. `rel` is now normalised to '/'. Run it on Windows: 0 failures. --- +## HW-vs-SW Lumen: MEASURED at last (2026-07-16 evening) — HW costs +20 ms/frame on the 760M + +The number EN-023 and EN-058(c) said nobody had ever measured. A/B on the +shooter (PERFTEST mode-1 gameplay, identical build, DXC DLLs present, PT off): + +| device features | gameplay | frame | +|---|---|---| +| EXPERIMENTAL_RAY_QUERY granted (HW Lumen active) | **14.4 fps** | ~69 ms | +| `BLOOM_FORCE_SW_GI=1` (SW hiz-screen/SDF trace) | **20.3 fps** | ~49 ms | + +Three consequences: + +1. **Granting the feature IS enabling HW Lumen.** ssgi_pass/gi_bake pick the + HW trace the moment the TLAS exists ("HW still wins over both when the + feature was granted"), and model_draw registers every skinned draw for + per-frame compute pre-skin + BLAS builds. There is no separate "HW Lumen + on/off" knob — dropping the DXC DLLs beside a shooter exe silently + converted it to the HW path and cost ~40% of its frame rate. docs/perf/014's + "within ~1.5×" guess is dead; on this iGPU the HW path costs +20 ms/frame. +2. **The boot line lies:** `ssgi trace backend = hiz-screen` is printed at + init, before the TLAS exists; per-frame the backend flips to HW with no + log. Diagnostics should report the backend actually used. +3. **The choice is quality-vs-frame-rate and belongs to the product owner** + per the standing no-quality-tradeoffs rule: HW trace sees real proxy + geometry (off-screen bounce, no screen-space artifacts); SW is 20 ms + cheaper here. Needs a GI screenshot A/B on this scene before any default + is picked. `BLOOM_FORCE_SW_GI=1` is the per-box escape hatch meanwhile. + ## EN-053 — Shadows cost ~5.3 ms in SAMPLING, and four passes each pay it ❌ *closed same day — the premise did not survive re-measurement* > **Measured before building (2026-07-16 evening, PERFTEST mode-0 bisect on