marfrit
20e3d004ae
Per user direction at cycle-4 close: file wd=16 (trend prediction validation) and vertical variants (column-stride TMU behaviour unknown) as local issues for future cycles. Progress instead to CDEF (AV1) for codec breadth. docs/issues/001 — wd=16 prediction validation. Per cycle 4 lesson 4, trend says wd=16 likely flips M4 negative. Quick incremental cycle when revisited. docs/issues/002 — vertical variants. Different memory access pattern (column-strided vs row-strided). The load-bearing unknown is whether the cycle 2 +6.9% mixed gain survives the TMU coalescing shift. If positive, deployment recipe gains symmetry; if negative, must split by orientation. Both issues have acceptance criteria + expected outcomes documented. Cycle 5 next: CDEF (AV1) — codec-breadth expansion. No Gitea repo exists for daedalus-fourier yet (project is local- only). If a tracker is wanted, create the repo and migrate these .md files. For now they live in-tree as part of the project history. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
72 lines
2.8 KiB
Markdown
72 lines
2.8 KiB
Markdown
# Issue 001 — VP9 LPF wd=16 cycle (prediction validation)
|
||
|
||
**Status**: open, not blocking
|
||
**Type**: kernel-cycle (cycle 5 candidate)
|
||
**Predicted verdict**: RED (M4 likely negative, per cycle 4 lesson 4)
|
||
**Priority**: low (incremental; trend prediction)
|
||
**Filed**: 2026-05-18
|
||
|
||
## Background
|
||
|
||
Cycle 4 (LPF wd=8) closed PASS with M4 delta +4.1 % vs cycle 2 wd=4's
|
||
+6.9 %. The downward trend prompted Phase 9 lesson: "wd=16 would
|
||
probably show further R degradation; M4 may flip negative based on
|
||
the trend line." See `docs/k4_lpf8_phase4_7.md §"Phase 9 lessons"`.
|
||
|
||
This issue tracks the experiment to validate (or invalidate) that
|
||
prediction.
|
||
|
||
## What to do
|
||
|
||
Cycle 5 LPF wd=16, mirroring cycle 4's compact structure:
|
||
|
||
1. **Phase 3**: build `tests/bench_neon_lpf16.c` modelled on
|
||
`bench_neon_lpf8.c`. NEON symbol: `ff_vp9_loop_filter_h_16_16_neon`
|
||
(already in vendored `vp9lpf_neon.S`). Capture M3.
|
||
2. **Phase 4-7**: write `src/v3d_lpf_h_16_16.comp` extending the
|
||
wd=8 kernel with the wd=16 outer-flat path (`flat8out` test, 14
|
||
writes per row when both flat8out and flat8in pass). New
|
||
contract: `dst_stride_u8 ≥ 14` (vs cycle 4's ≥ 6) because the
|
||
flat8out path writes at `base-7..base+6` (14 contiguous bytes).
|
||
3. **Phase 5 review**: mandatory — wd=16 is not as incremental as
|
||
wd=8 (much larger conditional logic, new contract bound).
|
||
4. **Phase 7**: measure M2, R; if M4 negative as predicted, document
|
||
trend confirmation and close kernel as "CPU-only" in deployment
|
||
recipe.
|
||
|
||
## Expected outcome (per prediction)
|
||
|
||
| Quantity | Predicted |
|
||
|---|---|
|
||
| M1 bit-exact | 100 % (same pattern as cycles 2/4) |
|
||
| M3 NEON | ~55 Medge/s (slightly faster than wd=8) |
|
||
| M2 QPU isolation | ~12-15 Medge/s |
|
||
| R isolation | 0.22-0.27 (ORANGE, downward) |
|
||
| M4 mixed vs NEON-4 | -2 % to +1 % (borderline; likely negative) |
|
||
| 30fps margin | still 5×+ (user-facing PASS regardless) |
|
||
|
||
## Acceptance criteria (issue closed when)
|
||
|
||
- Cycle 5 phases 1-7 complete, committed
|
||
- `docs/k5_lpf16_phase*.md` produced
|
||
- Phase 7 verdict documented, deployment recipe updated either way
|
||
- Phase 9 lesson 4 trend prediction validated or refuted
|
||
|
||
## Why deferred (not done in current session)
|
||
|
||
The session goal was "continue until user intervention necessary."
|
||
User directed: file as issue, progress to cycle 5 CDEF instead.
|
||
The trend prediction is interesting but the project's deployment
|
||
recipe is already locked through cycle 4; cycle 5 wd=16 result
|
||
would update at most one row of the recipe table.
|
||
|
||
## Related
|
||
|
||
- `docs/k4_lpf8_phase4_7.md §"Phase 9 lessons"` lesson 4 (the
|
||
prediction this validates)
|
||
- `external/ffmpeg-snapshot/libavcodec/aarch64/vp9lpf_neon.S`
|
||
(NEON ref already vendored — symbol `ff_vp9_loop_filter_h_16_16_neon`)
|
||
- `docs/k2_deblock_phase4.md` (cycle 2 template)
|
||
- `docs/k4_lpf8_phase4_7.md` (cycle 4 template, the most direct
|
||
reference)
|