Wave-2 PW5, the stage-6 experiment. Shipped behaviour is UNCHANGED: `max_inflight` is still 1.
Stage 6 is the frame-corruption stage, and its gate is an on-glass tear-hunt with a live compositor,
a real client and ten minutes of moving content. That is not runnable from here. But the depth-2
risk has two halves, and one of them lives entirely in this crate — the per-slot resources
(`cmd`/`fence`/`csc_set`/y/uv/cursor) and the alternating encoder handles — so that half can be
answered now, on the GPU, and the answer is worth having before anyone attempts the other.
The experiment drives the backend with two frames genuinely in flight (submit N+1, then poll N) and
compares the result against the encoder's OWN synchronous output over the same 16 moving frames.
Its own depth-1 decode is the honest reference: pyrowave's raw AU bytes are not reproducible
run-to-run (see the stage-3 commit), but its decoded planes are.
RESULT, .21 / RTX 5070 Ti (GPU idle at 180 MHz of 3090 — the slow-clock worst case on this card):
depth-2 vs depth-1 over 16 frames: worst-case PSNR identical (inf)
Bit-identical luma, every frame, in order. So stages 4 and 5 between them are sufficient for the
encoder side: doubling the six single-slot resources and alternating two `pyrowave_encoder` handles
under one monotonic wire sequence really does make overlap invisible to the decoder.
The test is built to fail rather than to pass. Content MOVES every frame (flat fills are the
documented false-green trap — a torn frame stitched from two halves of a static card is invisible),
it asserts two frames were ACTUALLY in flight rather than silently proving nothing, it asserts the
AU count is unchanged, and it carries an off-by-one discriminator that raw PSNR would miss: each
overlapped frame must match its own reference BETTER than it matches the previous one, so a
pipeline delivering frames one position late fails even though every individual PSNR looks fine.
It reaches `max_inflight` directly instead of through a shipped knob, precisely so the shipped
value stays 1.
⚠ WHAT THIS DOES NOT COVER, stated here so the next person does not read it as a green light for
stage 6: the CAPTURE side. `.process` hands the SPA buffer back to the compositor at callback
return while the encode thread holds only a dup of its dmabuf fd, so a second frame in flight
widens the window in which the producer may overwrite a buffer we are still reading by a full frame
period. Nothing in this crate can test that — it needs a live producer. Stages 1 and 2 are what
make it answerable (the pool census says how deep the producer's ring is; the Choice range asks for
headroom), and the on-glass hunt is what would settle it.
Gates green at CI parity.
enricobuehler
7d37fe450d