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docs(worklog): the tall panel pays ~3 us of rayon region per reflector (DROPPED, recovered) - #17
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The level-2 panel of a tall compact-WY QR is a chain of dependent reflectors, and the fork already threads each one through the generic column split, so the level-2 work is asked for on every reflector and answered with 1.13x (unblocked 4096x16 QR: 0.1957 / 0.1788 / 0.1731 / 0.1968 ms at 1 / 2 / 4 / 8 workers on four cores). What that costs is a fresh rayon region per reflector: 2.11 us over the sequential product of the same size with a hot pool, 3.83 us once a serial product separates two regions, which is 32-57 us of the panel's 173 us. Reusing the region across the chain is a work-model change -- the ledger's Thread policy row -- not a threshold, so this records the measurement instead of building half of it. Also recorded: the unblocked m x 16 QR is 34% slower threaded at m=1024 and 17% at 2048, so the rank-one arm's 8192-element floor is active through a losing range; that floor is load-bearing where it was measured and was not moved. No code change. Record: docs/worklogs/2026-10-14-tall-panel-region-cost.md
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Recovers the record from the closed PR #16. Its branch had been rebased onto
main— where both of its commits became empty because the conflict inPATCHSET.mdwas resolved in favour ofmain— so the branch ended up identical tomain, GitHub closed the PR, and the record and its ledger row never reachedmain(verified missing there).What is pushed here is the same commit (
911e897, "the tall panel pays ~3 us of rayon region per reflector"), rebased ontomain(88fec8d) with thePATCHSET.mdconflict resolved by keeping both rows — the mergedEVD and SVD factorisation floorrow and this one — which is the resolution the two changes need; neither replaces the other.Docs only: a work-log record for the tall panel question (
tlinalg-rs#46's open item), settled as DROPPED by measurement, and its ledger row.