jank_capture.py: one command owns the whole pipeline so provenance can
never be wrong (the failure mode this replaces: append-only logs spanning
processes, hand byte-offsets, tail-guessing, wrong-build data):
1. record build identity (versionName + apk sha256 + tag)
2. force-stop + DELETE it.log (file can then contain exactly ONE process)
3. cold launch, verify ResumedActivity (before and after)
4. scripted drags ('4,2,4' = 4s drag, 2s settle, 4s drag)
5. pull the complete log
6. report: PROVENANCE + jank_eval verdict + MISS forensics
verdicts: PASS(0) / FAIL(1) / SUSPECT(fitted grid) / INVALID(multi-process)
MISS forensics: groups consecutive misses into episodes, classifies each
(CHAIN-STALL / LOOP-STUCK / GUARD-REJECT / NO-WAKE-ITER) with a +-33 ms
all-thread context window (IT poll/ev/rd/dec/pc/rc/vsw/nvol, VSYNC
latency, PRES, FR, SLOWEV, DECODE, OTHR, INVK).
self-test: synthetic 120Hz log with a 30 ms stuck-poll episode.
jank_eval.py fixes found under emulator stress:
- auto-windows active threshold was circular: 0.75x the refresh rate
meant a JANKY app (low present rate) is never detected as active.
Now 0.4x rate / 250 ms buckets. (Emulated 60 Hz scroll at 30-40 Hz
present was invisible to the old threshold.)
- BUCK 500->250 ms required the density multiplier *2 -> *4 (forgot,
caught by stress: only the fastest spans were windowed).
- fallback period (no VSYNC lines) was a telescoping mean (spans idle
gaps: 391 presents over 23 s fit '59.6 ms'). Now median-of-deltas
snapped to standard rates. A fitted grid cannot prove drops/doubles:
verdict on it excludes them (stalls+lates+spread remain) and the
verdict is marked SUSPECT (exit 3) instead of PASS/FAIL.
- run_file now returns (ok, suspect); small-log early exit fixed.
Stress matrix on emulator (x86_64, 60 Hz SF) — all pass:
capture pipeline x3 (standard 4,2,4 / fast 1,1,1 / slow 6,2,6)
pause/resume mid-drag (teardown -> occluded -> resume burst)
determinism (identical report twice), multi-process -> INVALID,
explicit --windows, --period-ms override, no-VSYNC -> SUSPECT path,
small log -> exit 1, synthetic perfect 120 Hz -> PASS exit 0.
