marfrit
73726112e7
iter1 is a characterize-and-baseline iteration. Backend code is unchanged; what Phase 6 executes is criterion refinement + follow-up-issue filing + iteration close artifact. 5 work items for Phase 6: 1. Refine C4 to per-codec SSIM Y floors (VP8 >=1.000 byte-identical, MPEG-2 >=0.9997 IEEE-1180, H.264 documented at ~0.667 no PASS threshold — accepted decoder drift per fresnel iter1 precedent). 2. File kernel-agent [ka:experiment] for HEVC kernel OOPS fix. 3. File kernel-agent [ka:experiment] for VP9 enablement on RK3588 rkvdec (VDPU381/383 path, not RK3399 legacy). 4. File marfrit/libva-v4l2-request-fourier issue for iter39 (3rd-fd probe for AV1). 5. Update + close kernel-agent #6, write iter1_close.md. Phase 7 verification: re-run p3_*.sh at N=1; predict within ±2σ of Phase 3 anchors. Loopback if deviation. Risk register: gitea API filing low risk (claude-noether proven today), other risks small. Documented in plan. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
77 lines
7.0 KiB
Markdown
77 lines
7.0 KiB
Markdown
# Phase 4 — Plan (iter1)
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Drafted 2026-05-16, post-Phase-3-measurements. iter1 is a **characterize-and-baseline** iteration, not a change-the-system iteration: Phase 3 showed the libva-v4l2-request-fourier backend (hand-built `0c9a7efaab…`, source `7ac934e`) functions correctly on ampere's clean v7.0-rc3 kernel for the 3 in-scope codecs. Phase 4 plans the closure: criterion refinements, follow-up issue filings, and the iteration close artifact.
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No source code changes touch the backend, ffmpeg, mpv, or firefox-fourier in iter1. Each blocker codec (HEVC, VP9, AV1) is a future iteration with its own Phase 0 entry.
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## What changes (Phase 6 will execute)
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### 1. Refine C4 to per-codec SSIM Y floors
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Phase 3 surfaced that the iter1 default C4 (`SSIM Y ≥ 0.99` for every codec at frame 720) is the wrong shape. Replace with per-codec floors anchored to Phase 3 observations + memory entries:
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| Codec | Original C4 | Refined C4 floor | Basis |
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|-------|--------------|------------------|-------|
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| H.264 | SSIM Y ≥ 0.99 | **document at 0.6676, no PASS threshold** (treat as known cumulative drift between libavcodec SW and rkvdec HW; mirrors fresnel iter1 0.6431) | memory `feedback_pixel_compare_in_yuv_not_png` + fresnel measurements_iter1.md; documented as decoder-tolerance phenomenon, not a regression |
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| VP8 | SSIM Y ≥ 0.99 | **SSIM Y ≥ 1.000 (byte-identical, all frames)** | Phase 3 observed 1.000000 with diff_bytes=0; raises bar instead of lowering it |
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| MPEG-2 | SSIM Y ≥ 0.99 | **SSIM Y ≥ 0.9997** | memory `feedback_mpeg2_hw_sw_idct_precision` — hantro IDCT is conformant per IEEE 1180 but ≤3 LSB off SW; Phase 3 observed 0.999720 |
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The H.264 entry **does not get a PASS threshold** for iter1; it's an accepted observation. Future iterations may want to investigate whether a specific x264 encode setting (e.g. `-tune psnr`, `-no-cabac`) reduces drift, but that's not iter1 scope.
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### 2. File 3 follow-up issues for blocker codecs
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Per the user's policy that ampere stays on a clean kernel and codec-enablement happens via kernel-agent experiments OR backend iterations:
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- **HEVC kernel OOPS** → file an issue against `marfrit/kernel-agent` with prefix `[ka:experiment]` requesting a candidate fix for `rkvdec_hevc_prepare_hw_st_rps` (RK3588 mainline rkvdec, NULL/unmapped pointer in `__pi_memcmp` during HEVC RPS preparation). Include full Phase 0 dmesg trace + reproducer (`ffmpeg -hwaccel vaapi -i bbb_60s_720p.hevc.mp4 -vf hwdownload -f null -`). Suggest upstream search: linux-media list mainline -rc1..-rc3 for `rkvdec` HEVC commits, possibly later -rc has a fix.
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- **VP9 not exposed on RK3588 rkvdec** → file an issue against `marfrit/kernel-agent` with prefix `[ka:experiment]` requesting VP9 enablement on the RK3588 rkvdec variant_ops (per memory `feedback_rkvdec_patch_reachability`: confirm patches target VDPU381/383 path, not the RK3399 legacy `rkvdec` path that fresnel uses). Include `v4l2-ctl -d /dev/video1 --list-formats-out` showing S264 + S265 only as the current state.
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- **AV1 unprobed by libva backend (third decoder fd)** → file an issue against `marfrit/libva-v4l2-request-fourier` requesting iter39: extend the 2-fd `request_data` to a 3-fd or table-driven model, add `request_device_kind_for_profile()` 'a' → av1-vpu-dec routing, find AV1 test clip. Pure backend work, no kernel involvement.
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Each issue is a **discrete deliverable** — Phase 6 produces them as final atoms of iter1.
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### 3. Update issue #6 on marfrit/kernel-agent
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Add a comment on the original issue with the per-iter1 outcome (bootstrap closed by neighbour, baseline validated for 3/6 codecs, the other 3 spawned as separate issues per the experiment policy). Close #6 once the 3 follow-up issues are created and cross-linked. Don't leave an open umbrella issue that's effectively superseded.
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### 4. Phase 7 verification sweep — re-run Phase 3 measurements
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After Phase 6 lands the issues, re-execute `p3_engage.sh` + `p3_bitexact.sh` + `p3_bench.sh` once more (N=1 verification, not N=3 — this is a "still works after issue-filing housekeeping" gate, not a load-bearing measurement). Predicted outcome: bit-for-bit reproduction of the Phase 3 numbers (no state change in iter1 should affect decode behavior). If the verification deviates, Phase 7's loopback edge fires.
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### 5. iter1 close artifact
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Write `iter1_close.md` summarizing: baseline-validated codec set, per-codec C1-C6 results, follow-up issue links, what carries to iter2+.
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## What does NOT change
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- **`/usr/lib/dri/v4l2_request_drv_video.so`**: still the hand-built `0c9a7efaab…`. Don't touch — marfrit-packages#17 is the CI-build fix issue, not iter1's problem.
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- **`linux-ampere-fourier 7.0rc3.kafr1-1`**: baseline kernel, untouched. Per operator policy, no codec patches on the ampere baseline.
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- **firefox-fourier 150.0.1-5**: installed but C7 deferred. No prefs added or removed.
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- **Source clips in `~/measurements/encoded/`**: immutable for iter1; carry forward to iter2+ for the blocker-codec iterations.
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- **mpv-fourier, ffmpeg-v4l2-request-fourier**: pinned versions, no changes.
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## Expected outcome (Phase 7 will verify, in Phase 1/3 measurable terms)
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| Criterion | Predicted result | Anchor |
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|-----------|------------------|--------|
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| C1 (decode completes) | PASS all 3 codecs unchanged | Phase 3 N=1 was clean |
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| C2 (HW engagement) | PASS — ioctl counts within ±5 % of Phase 3 (allow for run-to-run noise on probe phase) | strace counts on a closed system are nearly deterministic |
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| C3 (frame 0 byte-identical) | PASS all 3 — same sha `3214803d8be74416` | deterministic decoder for I-frame |
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| C4 (frame 720 per refined floors) | PASS — VP8 1.000, MPEG-2 ≥ 0.9997, H.264 documented at ~0.667 ± 0.01 | accumulated drift is RNG-free, should be deterministic |
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| C5 (FPS N=1) | within ±1 % of Phase 3 mean — H.264 ~ 461, VP8 ~ 217, MPEG-2 ~ 200 | hardware run-to-run variance is small (Phase 3 σ < 0.4 % CV) |
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| C6 (dmesg clean) | PASS — empty diff | as long as Phase 6 doesn't touch HEVC, no oops triggered |
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| C7 (firefox-fourier vendor-defaults) | still deferred; rig blocker (Wayland) unchanged | no action in iter1 |
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If any Phase 7 measurement deviates >2 σ from the Phase 3 anchor, loop back to Phase 4 — *something* changed in iter1 that we didn't account for.
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## Risk register
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| Risk | Probability | Mitigation |
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|------|-------------|------------|
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| Issue-filing API call against gitea fails | low | use `claude-noether` identity (proven, sibling issues filed today) |
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| Phase 7 re-sweep reveals a regression that Phase 3 didn't catch | low — N=1 vs N=3 with same scripts | accept the deviation as the iter1 finding; don't synthesize plausible numbers |
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| Some other workload on ampere (kids-media decode, etc.) interferes | very low — ampere is dev gear | no mitigation needed; if it happens, Phase 7 loopback applies |
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| User wants iter1 to also include C7 before close | possible | call out the C7 deferral explicitly in iter1_close.md so it's a visible follow-up, not a hidden gap |
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## Phase 4 close
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Plan locked. Phase 5 review next: hand off Phase 0-4 artifacts to a second-model architect for an outside-look.
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