The 'callback arrives 3-6 ms late' model that invalidated render-ahead in
earlier sessions was a mislabeled STG field: the Choreographer callback
actually fires at edge+0.5 ms (measured from the VSYNC ftn/mon pair). With
the wake ON the edge, the held frame presented at render START lands at
edge+~1.5 ms (constant phase, 4 ms of deadline margin), and render spikes
(5-10 ms, the measured cause of the residual 1% drops + 1.5 ms phase
spread) only stretch the PREPARE phase of the frame held for the NEXT
slot — spikes stop delaying visible frames.
- lib.rs: RENDER_AHEAD_ACTIVE = locked again (was false)
- lib.rs/stg.rs: IT lines gain rcpu (CPU us inside do_render) — spike
classifier: rcpu≈render ⇒ Skia/driver CPU work; rcpu≪render ⇒ blocked
on GPU/driver
- hypotheses-120hz.md: model correction + sltest baseline + results
Emulator behavior verified: scroll, settle (transition flush), mid-drag
pause/resume (no black window), no AlreadyAcquired panics, held-frame
presents at 0.6-2.1 ms. Phone cadence measurement pending (phone out for
user use ~2h).
Greg Pomerantz
8f06b85376