Wave-2 PW4's outcome. The package proposed moving the producer-fence wait off the PipeWire loop
thread, and was pre-registered to be ABANDONED if the wait turned out to already be free. It is,
on every producer and vendor measured — including the one where implicit sync actually exists.
Steam Deck, RADV VANGOGH, gamescope producer (built in distrobox pf2, run on the host):
samples=300 mean_us=23 max_us=48 p50=<=100us p99=<=100us
signaled=0 no_fence=300 timed_out=0 failed=0
p99 in the first bucket is the plan's own abandonment condition, and the outcome split explains
why: 300 of 300 buffers reported NoFence. Same on both NVIDIA producers (gamescope and Mutter's
virtual output — the exact no-explicit-sync case the comment cites as the reason the wait exists).
So `wait_read_ready` here is one ioctl and a return, not a block. Moving it to the consumer side
would buy nothing measurable and would take on the hazard the package itself names — a slot holding
a not-yet-ready dmabuf, and `repeat_last` re-waiting a fence it already consumed. Not a trade worth
making for 23 microseconds.
The 100 ms budget stays: it guards a producer that DOES fence, which is a real thing even if
nothing in this fleet does it. KWin/AMD is the one combination still unmeasured, and the histogram
from the previous commit is deliberately kept as the way to re-check — run with PUNKTFUNK_PERF=1
and read the p99 bucket.
Comment-only; no behaviour change. Gates green at CI parity.
enricobuehler
8387e48ac6