LL perf (UI): LLLayoutStack's ~4% is unexplained by code reading #359

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opened 2026-10-04 14:09:28 +00:00 by sky_line · 0 comments

sky_line commented

2026-10-04 14:09:28 +00:00

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From the LL-origin inefficiency audit (finding U0). File/line references are from commit 0229f8872c; re-locate them before working.

LLLayoutStack's ~4% is unexplained by code reading

What was ruled out:
- updateClass() iterates instance_snapshot() of every stack every frame, including those inside hidden floaters (lllayoutstack.cpp:677-684). That is cheap.
- No permanently-dirty stack was found.
What inflates it: the profile zone sits before the early-out (:401-405).
Decisive test: count stacks with mNeedsLayout per frame and log the names.
Fix once proven: an intrusive dirty list.
Suspect.

Verify the cost (profile or timer) before and after changing it.

From the LL-origin inefficiency audit (finding U0). File/line references are from commit 0229f8872c; re-locate them before working. **LLLayoutStack's ~4% is unexplained by code reading** - **What was ruled out:** - `updateClass()` iterates `instance_snapshot()` of every stack every frame, including those inside hidden floaters (`lllayoutstack.cpp:677-684`). That is cheap. - No permanently-dirty stack was found. - **What inflates it:** the profile zone sits before the early-out (`:401-405`). - **Decisive test:** count stacks with `mNeedsLayout` per frame and log the names. - **Fix once proven:** an intrusive dirty list. - Suspect. Verify the cost (profile or timer) before and after changing it.

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