f2a7b32a75
1 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
| 0a50f9b832 |
120Hz: fix the ALooper wake-fd race (root cause of slot drops) + phase-slip-robust referee
ROOT CAUSE of the 8-12% slot drops (uniform dec=1/0/1/0: locked, no wake seen, dirty, no render): AOSP Looper::pollInner (system/core/libutils/ Looper.cpp) drains the wake fd in the SAME epoll batch (up to 16 fds) as any ready input fd, and pollOnce returns the input's ident — the POLL_WAKE result is a local that gets dropped. ALooper_wake's byte is consumed WITHOUT PollEvent::Wake ever reaching Slint, unrecoverable. With motion events arriving 1-4 ms after the edge (always for a real 120-240 Hz finger; ~1 in 5 frames for 20 Hz adb input) the wake is lost and the locked decision (saw_wake && slot-guard) drops the dirty frame for that slot. Fix (vendor backend): a dedicated eventfd registered with the MAIN looper under ALOOPER_POLL_CALLBACK. The Looper invokes the C trampoline INSIDE pollInner (before pollOnce returns, regardless of which ident is handed back), so delivery can never be swallowed by a co-batched input response. - frame_callback: note the edge, write the eventfd, then ALooper_wake (secondary). The fd is leaked: it belongs to the main looper for the process lifetime. - trampoline: DRAINS the eventfd (level-triggered — without the drain the counter stays >0, the fd stays readable and the loop busy-spins on POLL_CALLBACK at ~10 kHz: 1812 spin iterations measured) and publishes the edge into delivered_edge. - main loop: saw_wake |= (delivered_edge newer than last seen). - DIRTY BACKSTOP: the 6 ms poll cap was never a backstop — timeout iterations have saw_wake=false so the locked decision never rendered (the 20-40 ms silences). Now: dirty && last render >= 2 slots old renders regardless of wake state. Measured on the phone (Pixel 9 Pro, 120 Hz, sltest, identical capture): buildC (before): 127 drops + 12 stalls in 1142 frames buildE (after): 8 drops + 0 stalls in 1266 frames Phase (p10-p90): 0.72-1.00 ms in all windows. Remaining 8/1266 (0.63%) are slip-and-recover pairs where the UI thread is DESCHEDULED 6-8 ms while sleeping in epoll (wakes arrive on time, cb-lat 0.5 ms) — EAS scheduling variance, no app-side contention in sltest. Referee fixes found while judging this data (tools/jank_eval.py): - NEAREST-OBSERVED-EDGE slot grid: the 120 Hz panel clock phase-slips after idle blanking (re-locks at arbitrary phase), invalidating any grid anchored at ftns[0]. An entire drag window read late=230/ dropped=24 while per-cycle tracing showed presents at edge+2.0 ms. slot_of_ftn assigns each present to the nearest observed hardware edge in a time-continuous slot domain (slip-immune: a constant delta shifts all slots, differences preserved; stall-accurate: ftn times are CLOCK_MONOTONIC). - tools/jank_capture.py: capture is INVALID unless the screen is Awake AND the keyguard is down (a run on a sleeping phone silently injects no input: 49 IT lines, 1 present). |
