marfrit
356e446a49
Third daedalus-fourier kernel — VP9 8-tap regular subpel filter,
horizontal direction, 8-wide output. Multiply-heavy by design to
stress V3D's no-DP4A deficit. Full cycle Phase 1-7 + M4'''.
Phase 5''' second-model review delivered cleanly — caught 1 RED
bug pre-implementation (src_off off-by-3 indexing convention) and
2 YELLOW gaps (assert MUST language, shaderdb filter-LUT gate).
Without the review, M1''' would have failed silently on first run
with cryptic "high-index source pixels wrong" symptoms.
Phase 6 v1 first-light: M1''' 100.0000% bit-exact (65536/65536
blocks across all 16 mx phases). Phase 5''' filter-LUT prediction
materialised exactly: 197 uniforms (gate was 144), 2 threads (down
from cycle-2's 4 due to register pressure).
Performance:
M2''' = 1.413 Mblock/s (707.9 ns/block)
M3''' = 20.997 Mblock/s (NEON baseline phase3)
R''' = 0.067 (RED band — structural mismatch)
shaderdb: 488 inst, 2 threads, 197 uniforms, 25 max-temps, 0 spills
M4''' concurrent matrix (8s windows):
NEON 1-core 14.479 Mblock/s
NEON 4-core 15.248 Mblock/s <- baseline (compute-bound,
not bandwidth-saturated
like cycles 1+2!)
QPU only 1.380 Mblock/s
MIXED NEON-3 + QPU 12.277 Mblock/s <- -19.5% (FAIL gate)
MIXED NEON-4 + QPU 12.158 Mblock/s <- -20.3%
NEW cross-cycle finding (Phase 9 lesson 2): compute-bound CPU
workloads make the QPU-offload story collapse. Cycles 1+2 were
bandwidth-saturated (4-core scaling 0.56-0.82x of 1-core), so
freeing a CPU core via QPU offload added throughput. Cycle 3 MC
is compute-bound (4-core scaling 1.05x of 1-core — near-linear),
no free cycles to free. QPU contribution (0.45 Mblock/s in
contention) doesn't compensate for losing 1 NEON core delivering
~3.8 Mblock/s.
But 30fps@1080p floor: PASS in every config (1.4x to 15.7x
isolation margin). Per project_30fps_floor_is_fine.md, user-facing
test never fails — daily YouTube playback works fine on any CPU/QPU
split.
DEPLOYMENT RECIPE for higgs (cycle 3 confirmed split):
IDCT (k1) -> QPU (R=0.92, +7% mixed, frees CPU core)
LPF (k2) -> QPU (R=0.41, +7% mixed, frees CPU core)
MC (k3) -> CPU (R=0.067, -19.5% mixed — stays on CPU)
Entropy -> CPU (structurally serial)
Mixed-substrate deployment, not "QPU does everything". Realistic for
higgs: entropy + MC on 2-3 ARM cores; IDCT + LPF dispatched to QPU
concurrently; 1-2 ARM cores left for vscode etc.
New artifacts:
- src/v3d_mc_8h.comp — GLSL kernel
- tests/vp9_mc_ref.c — standalone C ref (REGULAR filter
embedded; clean transcription)
- tests/bench_neon_mc.c — M1'''_c + M3''' bench
- tests/bench_v3d_mc.c — M1''' + M2''' bench with contract
asserts + 30fps margin display
- tests/bench_concurrent_mc.c — M4''' pthread bench
- external/ffmpeg-snapshot/libavcodec/aarch64/vp9mc_neon.S (vendored)
- external/ffmpeg-snapshot/libavcodec/vp9_subpel_filters_table.c
(hand-extracted; provides
ff_vp9_subpel_filters symbol
without dragging in full vp9dsp.c)
- docs/k3_mc_phase{1,2,3,4,5,7}.md — full cycle documentation
Memory updates: project_30fps_floor_is_fine.md (user's 30fps target
recalibration), MEMORY.md index updated.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
78 lines
2.5 KiB
Markdown
78 lines
2.5 KiB
Markdown
---
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cycle: 3
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phase: 3
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status: closed 2026-05-18
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date_opened: 2026-05-18
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parent: k3_mc_phase2.md
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host: hertz
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---
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# Cycle 3, Phase 3 — NEON M3''' baseline
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## Raw
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```
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=== M1'''_c bit-exact (10000 random blocks) ===
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M1'''_c correctness: 10000 / 10000 blocks bit-exact (100.0000%)
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mx phase coverage: min=577 max=668 (16 phases sampled)
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=== M3''' NEON throughput ===
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M3''' NEON throughput:
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blocks/batch: 65536
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batches done: 939
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total blocks: 61 538 304
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elapsed (kernel)=2.930751 s
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elapsed (setup) =2.075477 s
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throughput = 20.997 Mblock/s
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per-block = 47.6 ns
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equiv 1080p = 648.1 FPS (32400 blocks/frame)
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```
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## Numbers
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| | |
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|---|---|
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| **M1'''_c (bit-exact)** | **100.0000 %** vs `daedalus_vp9_put_regular_8h_ref` |
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| mx coverage | all 16 phases sampled, uniformly within ±10 % of expected count |
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| **M3''' (throughput)** | **20.997 Mblock/s** single-core |
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| per-block | 47.6 ns |
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| cycles/block | 47.6 ns × 2.8 GHz ≈ 133 cycles |
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| 1080p FPS-eq | 648 FPS |
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## Comparison across cycles
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| | IDCT (k1) | LPF (k2) | MC (k3) |
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|---|---|---|---|
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| Per-unit ns (NEON) | 122 | 20.7 (per edge) | 47.6 |
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| 1080p FPS-eq | 252 | 748 (worst edges) | 648 |
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| Compute character | Q14 butterflies + transpose | abs+compare+small mults | 8-tap convolution, mult-heavy |
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| NEON win | SMLA + transpose | SMULL + saturate | SDOT-style packing |
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MC NEON is fast — at ~2.6× IDCT throughput per unit. The A76's SDOT
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or SMULL-pair pattern handles 8-tap convolution extremely well; this
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is precisely the workload NEON SIMD was built for. **The QPU's
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break-even point on cycle 3 is correspondingly tight.**
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## Predictions for M2''' / R'''
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V3D 7.1 has SMUL24 (8b×8b → 16b sufficient) but **no DP4A**, so the
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QPU must do 8 separate SMULL + ADD per output pixel. Bandwidth-wise
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MC is similar to LPF (~6 MB / 1080p frame). Compute-wise much heavier
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than LPF.
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- Compute-envelope (idealised): 32 400 blocks × 1 150 ops = 37 Mops
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per frame. At v3d 92 GFLOPS theoretical × 23 % util ≈ 21 GOPS
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effective → 1.8 ms / frame → 540 FPS → 17.5 Mblock/s
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- Bandwidth-envelope: 5.9 MB/frame ÷ 4 GB/s ≈ 1.48 ms/frame → 22 Mblock/s
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- Combined: min(compute, bandwidth) ≈ 17.5 Mblock/s
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**Predicted R''' = 17.5 / 21.0 ≈ 0.83** isolation. Likely YELLOW
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band by a small margin.
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Honest lower bound: if SMUL24-vs-DP4A penalty is bigger than
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estimated (CPU SDOT does 4 INT8 MACs in one instruction; the QPU
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needs 4× more cycles for the same work in the worst case), R'''
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could land near 0.5-0.6. Phase 7''' measures.
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Phase 4 next.
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