Wave-2 PW4, step one of one-so-far. The package's own first line is "investigation step first
(measure, then decide)", and it is pre-registered to be ABANDONED if the wait's p99 is ~0 — so the
instrument ships before the change, not after.
A per-session histogram of `wait_read_ready`, taken on the PipeWire loop thread, which is exactly
where the wait is expensive: that thread is the compositor's consumer, so time blocked there delays
buffer recycling for the NEXT frame. Logged under PUNKTFUNK_PERF at the same cadence and gate the
encode backends use for their submit splits, so a perf run reads as one instrument: samples, mean,
max, p50/p99 bucket, and the Signaled/NoFence/TimedOut/failed split.
Buckets are coarse on purpose (100us -> 10ms, plus overflow). The decision this feeds is binary —
a p99 in the first bucket means the wait is already free and PW4 becomes a comment correction; a
p99 past 1ms is a real stall against a 16.6ms frame budget. Edges are placed so those two worlds
cannot be confused, and anything past the last edge reports as overflow rather than clamping into
the top bucket ("worse than 10ms" is a distinct finding).
The outcome split sits next to the timings because "the wait is short" and "there is nothing to
wait for" are different results with different consequences, and one data point already shows the
second: on gamescope/NVIDIA the probe reports NoFence, i.e. that producer attaches no implicit
fence at all.
5 tests pin the arithmetic, including that an empty histogram reports "no answer" rather than a
decisive-looking zero — the failure mode that would retire the package on no evidence.
No behaviour change: the wait still happens where it always did. Gates green at CI parity.
enricobuehler
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