marfrit
be7ff5587c
Second kernel candidate per phase7_M4.md verdict "next-kernel cycle
authorised". VP9 4-tap inner loop filter, horizontal direction,
8-pixel edge (libavcodec ff_vp9_loop_filter_h_4_8_neon as baseline).
Different workload shape from IDCT - boundary streaming, lighter
compute per unit, per-row conditionals - tests whether QPU win
generalises.
docs/k2_deblock_phase1.md - goal-setting. Same R-band decision rules
as cycle 1 (phase1.md), with the cycle-1 calibration adjustment:
ORANGE band is no longer auto-close because M4 showed mixed > pure
CPU even at modest R when CPU bandwidth-saturates.
docs/k2_deblock_phase2.md - situation analysis. C reference already
in vendored snapshot (vp9dsp_template.c:1780-1898). Fetched
vp9lpf_neon.S fresh (1334 lines, LGPL-2.1+, FFmpeg n7.1.3 pin,
SHA-256 384e49e7...). PROVENANCE.md updated.
docs/k2_deblock_phase3.md - NEON baseline:
M1''_c bit-exact 100.0000 % (10000 random edges)
M3'' throughput 48.285 Medge/s (20.7 ns/edge, single A76)
per-frame 1080p-eq 748 FPS (worst case 64 530 edges/frame)
cycles/edge ~58 (=20.7ns x 2.8GHz), ~7 cycles/row
LPF is 5.9x faster per-unit than IDCT M3 (20.7 vs 122 ns), so the
QPU break-even point moves down. Predicted R''_v1 band ~0.5-0.9
- frame-level batching amortises the same 33us dispatch overhead;
workload becomes bandwidth-bound rather than compute-bound
(~5.7 MB/frame traffic at 64 530 edges x ~88 B per edge).
New artifacts:
- tests/vp9_lpf_ref.c - standalone bit-exact C ref (8-bit, wd=4
inner only; clean transcription)
- tests/bench_neon_lpf.c - M1''_c gate + M3'' time-based bench
(5s window, edge-content-biased RNG for
realistic fm/hev hit rates)
- external/ffmpeg-snapshot/libavcodec/aarch64/vp9lpf_neon.S
- CMakeLists.txt updated with bench_neon_lpf target
Phase 4 next: plan the QPU LPF compute shader. Cycle 1's phase4.md
+ phase5.md + phase7.md learnings apply directly - bake in the v4
winning patterns from the start (WG=256, edges-per-subgroup
pattern adapted from blocks, uint8_t dst SSBO, oob flag, unrolled
writes).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
94 lines
3.8 KiB
Markdown
94 lines
3.8 KiB
Markdown
# FFmpeg source snapshot
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Verbatim subset of FFmpeg source pinned for use as reference
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implementations of the VP9 8×8 inverse DCT (Phase 1 target of
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`daedalus-fourier`). See `../../docs/phase2.md §2` and `§5` for
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the rationale.
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## Upstream pin
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- **Repository**: https://github.com/FFmpeg/FFmpeg
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- **Tag**: `n7.1.3` (matches `libavcodec61 8:7.1.3-0+deb13u1+rpt1`
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shipping in Debian Trixie on the dev host `hertz`)
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- **Annotated tag object**: `0a9a757e96fdf053697084bbd1f620edeac9d084`
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- **Commit object (tag target)**: `f46e514491172d15bd74b4abb1814cd2f05a763e`
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- **Snapshot fetched**: 2026-05-18 (UTC), via
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`https://raw.githubusercontent.com/FFmpeg/FFmpeg/n7.1.3/<path>`
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## Files in this snapshot
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All files are byte-for-byte copies of the upstream source at the
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tagged commit, no modifications.
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| Path | Lines | Bytes | SHA-256 |
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|---|---|---|---|
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| `libavcodec/vp9dsp_template.c` | 2578 | 89045 | `41b21f667a6c497b620aa1637d8269badc45d1ac7e621d694441c5bf39356e4f` |
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| `libavcodec/aarch64/vp9itxfm_neon.S` | 1580 | 63534 | `82ee3ceed4735c63576bafdcee28e2215652743ade55a9eab46a16d9530369f6` |
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| `libavcodec/aarch64/vp9lpf_neon.S` | 1334 | — | `384e49e7a6e838d9e38aedc00838ed4aebfa6c5bdb343ecaf23ef639bc10fbb7` |
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| `libavcodec/aarch64/neon.S` | 173 | 7496 | `72d36ce6c3fcc5e53de869cfe10fda16225ebe580c32891bccc240a30a85a538` |
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| `libavutil/aarch64/asm.S` | 260 | 8069 | `c0d03143b1bc5a9e358222d08d2d449d595271844fe7a3dc23bffb91abe8b0e3` |
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| `COPYING.LGPLv2.1` | 502 | — | `b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe` |
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Verify with:
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```sh
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( cd external/ffmpeg-snapshot && sha256sum -c <<'EOF'
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41b21f667a6c497b620aa1637d8269badc45d1ac7e621d694441c5bf39356e4f libavcodec/vp9dsp_template.c
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82ee3ceed4735c63576bafdcee28e2215652743ade55a9eab46a16d9530369f6 libavcodec/aarch64/vp9itxfm_neon.S
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72d36ce6c3fcc5e53de869cfe10fda16225ebe580c32891bccc240a30a85a538 libavcodec/aarch64/neon.S
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c0d03143b1bc5a9e358222d08d2d449d595271844fe7a3dc23bffb91abe8b0e3 libavutil/aarch64/asm.S
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b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe COPYING.LGPLv2.1
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EOF
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)
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```
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## License
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LGPL-2.1-or-later. See `COPYING.LGPLv2.1`. Original copyright
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holders include the FFmpeg authors and Google Inc. (2016) for
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the aarch64 NEON paths. The snapshot inherits FFmpeg's license
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in full.
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## Why each file is in this snapshot
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- `libavcodec/vp9dsp_template.c` — contains `idct_idct_8x8_add_c`,
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the bit-exact C reference for the Phase 1 kernel under test (M1).
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- `libavcodec/aarch64/vp9itxfm_neon.S` — contains
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`ff_vp9_idct_idct_8x8_add_neon`, the NEON throughput baseline
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(M3). Also defines `idct8`, `dmbutterfly0`, `dmbutterfly`,
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`dmbutterfly_l`, `butterfly_8h`, and the `idct_coeffs` constant
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table.
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- `libavcodec/aarch64/neon.S` — defines `transpose_8x8H` used by
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`vp9itxfm_neon.S`.
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- `libavutil/aarch64/asm.S` — defines `function`, `endfunc`,
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`movrel`, `const`, `endconst`, and other assembly preamble
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macros required to assemble the above NEON files.
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## Re-vendoring procedure
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If the upstream pin needs to change (e.g., hertz updates to a
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newer libavcodec):
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```sh
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TAG=nX.Y.Z
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BASE=https://raw.githubusercontent.com/FFmpeg/FFmpeg/$TAG
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cd external/ffmpeg-snapshot
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for f in libavcodec/vp9dsp_template.c \
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libavcodec/aarch64/vp9itxfm_neon.S \
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libavcodec/aarch64/neon.S \
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libavutil/aarch64/asm.S \
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COPYING.LGPLv2.1; do
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curl -sSf -o "$f" "$BASE/$f"
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done
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sha256sum libavcodec/vp9dsp_template.c \
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libavcodec/aarch64/vp9itxfm_neon.S \
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libavcodec/aarch64/neon.S \
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libavutil/aarch64/asm.S \
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COPYING.LGPLv2.1
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# update this PROVENANCE.md with the new tag, commit hash, and hashes
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```
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After re-vendoring, re-run the bit-exact gate (M1) and throughput
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baseline (M3) — both can shift across FFmpeg versions even when
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the VP9 spec doesn't change (e.g., NEON micro-optimizations).
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