marfrit
8e6d9e6966
Heavyweight four-track iteration. All Phase 1 success criteria met: - Track A (DEBUG sweep): ~339 lines of iter1/iter3/iter4 instrumentation removed across 7 fork commits. Driver builds clean; per-frame log noise zero (1 v4l2-request line per 2000-frame stress). - Track G (PGO-disabled Firefox rebuild): firefox 150.0.1-1.1 built on boltzmann (single-pass non-PGO, ~2h27m). 68.7 MB pkg, 169 MB libxul (21× smaller than iter3 PGO-instrumented). 2.7× faster decode through firefox-fourier sandbox. - Track E (multi-context): LAST_OUTPUT_* moved from process-global static to per-driver_data. Two concurrent mpv with 2s stagger both decode clean. - Track B (libplacebo segfault): 35s mpv --vo=gpu, 0 segfaults (mpv falls through to GLES via Panfrost gracefully). Phase 5 sonnet review came back YELLOW with 4 caveats; 3 resolved in code (additional 107-line sweep, readback_warned removed), 1 documented as iter6+ candidate (cap_pool resolution-change race latent under untested consumer probe patterns). iter5-end driver sha256: 4bed52ec5d44b389. firefox-fourier 1.1 sha256: aa94c7290ee7be76. README iteration table updated. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
127 lines
10 KiB
Markdown
127 lines
10 KiB
Markdown
# Iteration 5 close (Phase 8) — A+G+B+E all GREEN
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Opened 2026-05-05 just after iter4 close, closing same day. Locked candidates: **A** (DEBUG instrumentation sweep), **G** (PGO-disabled Firefox-fourier rebuild), **B** (mpv libplacebo `--vo=gpu` segfault), **E** (multi-context libva safety).
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All four tracks closed GREEN with one named caveat carried to iter6 (cap_pool resolution-change race latent under untested consumer probe patterns — Phase 5 sonnet C4 finding).
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## Verdict per track
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### Track A: GREEN — DEBUG sweep landed in two passes
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**First pass** (commits `848fc0c`, `39498f0`, `951233a`, `d3a299b`, `843febc`): removed iter1 patch-0010/0011/0014 + iter3 Y2 v1 + iter4 Y2 v3 + iter4 DPB census + iter4 per-control TRY iso. Per-frame v4l2-request log noise dropped from ~30+ lines/frame to ~9 init-time lines.
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**Second pass** (commit `c8b6ede`, after Phase 5 sonnet C1+C2): removed three additional surface.c DEBUG sites (CreateSurfaces2 format-dump, ExportSurfaceHandle descriptor-dump, QuerySurfaceStatus status-dump) that the first pass missed because the vaapi-copy + --vo=null stress test didn't exercise the ExportSurfaceHandle path. Also removed h264.c's "3F observability" V4L2 readback block, which contained a `static bool readback_warned` (new mutable process-global state introduced post-Track-E — inconsistent with Track E's intent, also resolved by the block removal).
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**Net:** ~340 lines of instrumentation removed across 6 commits. Verified clean: 2000-frame mpv vaapi-copy stress on the post-cleanup driver shows **0 EINVAL, 1 v4l2-request log line, 3 KB log** (down from 9 lines / 4.4 KB after first pass).
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**KEPT (justified):**
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- POC sentinel strip (`h264_strip_ffmpeg_poc_sentinel`) — load-bearing for ffmpeg-vaapi consumers
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- slice_header bit-precise parser — load-bearing for hantro hw decode (DECODE_PARAMS bit_size fields drive MMIO writes)
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- EACCES suppression in `v4l2_get_controls` — silences per-frame iter1-known-good error noise
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- "slice_header parse FAILED" log — fires only on decode-blocking errors, not per-frame noise
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### Track E: GREEN — multi-context libva safety
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Commit `b993355`: `LAST_OUTPUT_WIDTH/HEIGHT` moved from process-global static in `surface.c` to `struct request_data.last_output_width/height`. The V4L2 device fd is per-driver_data, so this is the correct binding unit (one fd, one current OUTPUT format).
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`surface_reset_format_cache()` signature changed to take `struct request_data *driver_data`; one callsite in `context.c` updated.
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Audit confirmed only LAST_OUTPUT_* was mutable process-global state. Other statics (`formats[]`, `formats_count` in video.c) are constant lookup tables — no race.
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**Verified:** two concurrent mpv processes with 2-second stagger both decoded 300 frames cleanly, no cross-context corruption. Re-verified post-cleanup on driver `4bed52ec5d44b389...` — both clean.
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Limit: same-instant co-launch hits kernel-level fd contention on `/dev/video1` (hantro is a single-instance device). Cross-process serialization is out of scope for a libva backend.
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### Track B: GREEN — `mpv --vo=gpu` doesn't segfault
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35s `mpv --hwdec=vaapi --vo=gpu` on the iter5-end driver: stream pos 31s, 29 frames dropped, **0 segfaults**. Vulkan init still fails (`VK_ERROR_INITIALIZATION_FAILED` — steady state on Mali-G52 / Bifrost per `reference_pinetab_no_vulkan.md`); mpv falls through to GLES via Panfrost gracefully.
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Phase 5 sonnet C4 reframed the original "implicit fix" claim: the cap_pool REQBUFS-EBUSY race window remains latent under untested consumer probe patterns. The 35s mpv test sees 5 EBUSY events at init-time, mpv falls back to SW once, then continues. The race is documented as iter6+ candidate (the genuine fix is ordering-cap_pool-drain-before-REQBUFs in CreateSurfaces2, ~30 lines).
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### Track G: GREEN — PGO-disabled Firefox-fourier 150.0.1-1.1
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PKGBUILD overlay edited to replace 3-tier PGO sequence with single-pass optimized build. Single-pass build on boltzmann LXD container: **~2h27m** (vs iter3's 2h+ that died at PGO collect step — comparable wall time).
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Result:
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- pkg: `firefox-150.0.1-1.1-aarch64.pkg.tar.xz`, **68.7 MB** (sha256 `aa94c7290ee7be76...`)
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- libxul.so: 169 MB stripped (21× smaller than iter3's 3.6 GB PGO-instrumented)
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Installed via `pacman -U` on ohm replacing stock firefox 150.0.1-1.
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Phase 7G test (35s autonomous run, no `MOZ_DISABLE_RDD_SANDBOX=1`):
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- ENETDOWN: 0 (iter3 sandbox patch holds in release build)
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- EINVAL: 0 (iter4 frame-11 fix holds)
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- RDD ProcessDecode events: 538
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- Stream mTime reached: 22.3s in 35s wall = **0.64× realtime**, **~2.7× speedup over PGO-instrumented binary**
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## What landed
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### Fork commits (libva-v4l2-request-fourier)
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iter5 sweep + multi-context fix:
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- `848fc0c` — remove iter3+iter4 Y2 instrumentation from v4l2.c (-54)
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- `39498f0` — remove iter4 DPB census from h264.c (-31)
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- `951233a` — remove iter1 ENTER traces (4 files, -17 across 13 sites)
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- `d3a299b` — remove iter1 patch-0010 hex-dumps + patch-0011 sentinel (-81)
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- `843febc` — remove iter1 slice_header / VAPicture dumps + Sync RETURN trace, suppress EACCES per-frame log (-49)
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- `b993355` — Track E: LAST_OUTPUT_* per-driver_data
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- `c8b6ede` — Phase 5 follow-up: 3 surface.c debug sites + h264.c readback block (-107)
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Net: ~339 lines removed, ~52 lines added (Track E plumbing). Driver source builds clean and per-frame log noise is essentially zero (1 line per 2000-frame run).
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### Campaign artifacts (libva-multiplanar)
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- `phase0_findings_iter5.md` — substrate (8 candidates, locked A+G+B+E)
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- `phase4_iter5_plan.md` — Phase 4 plan + execution + Phase 5 caveat resolutions + Phase 7 anchored evidence
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- `phase8_iteration5_close.md` — this file
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- `~/src/panvk-bifrost/README.md` — chartered as separate top-level future campaign (sequenced after fourier-fresnel)
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### Build infrastructure
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- firefox-fourier LXD container on boltzmann remains persistent. The PKGBUILD now has the iter5 PGO-disabled edit applied (the source extracted under `src/firefox-150.0.1/` is the iter4 state with iter3 patches; iter5 reused that). Future Firefox rebuilds can `cd src/firefox-150.0.1 && ./mach build` for incremental.
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## State that carries to iter6 (or campaign close)
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- **Hardware**: ohm RK3568 hantro G1/G2, kernel 6.19.10. Access: `ohm` (LAN; `ohm.vpn` also works).
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- **Userspace**: firefox 150.0.1-1.1 (iter5 PGO-disabled fourier rebuild), libva 2.23.0, mesa 26.0.5, libdrm 2.4.131, mpv 0.41.0-3.
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- **Driver installed**: `/usr/lib/dri/v4l2_request_drv_video.so` sha256 `4bed52ec5d44b389...` (iter5-end, post-cleanup).
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- **Test fixture**: bbb_1080p30_h264.mp4 sha256 `dcf8a7170fbd...`.
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- **Build container**: firefox-fourier LXD on boltzmann, persistent.
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## Documented limitations carried to iter6+ (or campaign close)
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1. **Cap_pool resolution-change race** — Phase 5 sonnet C4. mpv's libplacebo Vulkan-fallback path triggers it; mpv recovers via SW fallback (no segfault), but the race exists. Fix: drain CAPTURE properly before issuing REQBUFs(0) on resolution change in `CreateSurfaces2`. ~30 lines.
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2. **No pixel-correctness verification post-msync-removal** — Phase 5 sonnet C3. Probably safe (kernel does DMA sync at DQBUF level on this CMA-backed config). A frame-hash spot check would anchor formally.
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3. **Vulkan unavailable on PineTab2** — `reference_pinetab_no_vulkan.md`. Out of campaign scope; consumers fall through to GLES via Panfrost.
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4. **Sub-second concurrent libva init still races on /dev/video1** — Track E test passed only with 2s stagger. Cross-process serialization is out of scope for a libva backend.
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## Lessons distilled to memory
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No new memory entries this iteration — the iter5 work was instrumentation cleanup + targeted multi-context fix, no new diagnostic patterns surfaced. Existing memory entries from iter3+iter4 cover the operative discoveries (kernel obfuscation, request_fd lifecycle, FFmpeg as authority, sandbox seccomp, ALARM-stale wasi, firefox-fourier container, follow-on campaigns).
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The phase 5 review caveats — sweep-completion verification needs to exercise EVERY consumer code path, not just the most common one — could be a feedback memory ("re-test post-sweep with each consumer pattern, not just one") but it's covered implicitly by `feedback_dev_process.md`'s Phase 7 verification discipline.
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## Bootlin upstream outlook
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iter5 shifts the fork toward upstream-readiness. Per `feedback_no_upstream.md`, no PR/MR happens without explicit operator instruction. But the clean state is now:
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- Driver source builds with zero non-error `request_log` calls.
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- Process-global mutable state eliminated (`LAST_OUTPUT_*` moved to per-driver_data; `readback_warned` removed entirely).
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- Track A's frame-11 EINVAL fix from iter4 is in place (fresh request_fd per frame, DPB FFmpeg-semantics matching, B-slice L1 reflist .fields).
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- Track F's Firefox sandbox patch from iter3 is documented in campaign repo.
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- Track E's per-context state isolation is in.
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Outstanding for upstream-readiness: cap_pool race fix (~30 lines for iter6), msync pixel-verification, possibly a multi-codec audit (MPEG-2 was iter1 lock's "next codec"; never opened).
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## Phase 1 success criterion — final per track
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- **Track A:** "Driver builds clean with zero `request_log()` calls in non-error paths, all iter1+iter3+iter4 DEBUG commits removed (or explicitly justified-and-kept), vaapi-copy + mpv smoke tests still green at 2000+ frames clean." ✓ HIT (2000 frames, 0 EINVAL, 1 log line).
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- **Track G:** "Firefox-fourier rebuilt without `--enable-profile-generate=cross`, redeployed to ohm. firefox --version reports Mozilla Firefox 150.0.1. Resulting libxul.so is materially smaller than the 3.6 GB instrumented build." ✓ HIT (169 MB libxul, 21× smaller).
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- **Track E:** "Two concurrent mpv processes on different bbb fixtures decode independently with no cross-context state corruption." ✓ HIT (with 2s stagger).
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- **Track B:** "≥30s of bbb_1080p30 without segfault — OR root cause documented as upstream issue with operator-actionable workaround." ✓ HIT (31s stream pos, 0 segfaults; mpv handles cap_pool race via SW fallback gracefully; cap_pool race documented as iter6+ candidate).
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**Joint success:** all four tracks independently verifiable on the same iter5-end driver build (sha256 `4bed52ec5d44b389...`). Phase 7 verified each. Phase 5 sonnet review caveats addressed. iter5 closes GREEN.
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