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marfrit 2dd774a9ab Issue 003 closed: mixed-kernel M4 validates V4 deployment shape 
bench_concurrent_mixed runs NEON-N on kernel A + QPU on kernel B
concurrently. Matrix on hertz:

  V3 (CPU MC + QPU MC same-kernel): CPU 22.64 + QPU 0.39 Mblock/s
  V4 (CPU MC + QPU LPF4):            CPU 27.87 + QPU 12.74 Medge/s
  V1 (CPU MC + NEON-fb CDEF):        CPU 24.49 + 1.75 Mblock/s CDEF
  V2 (CPU LPF4 + NEON-fb CDEF):      CPU 27.28 Medge + 1.70 Mblock/s

V4 is the daedalus-fourier deployment shape (CPU runs MC; QPU runs
LPF4 via cycle 2 GREEN offload). Both substrates productive; CPU
MC +23% per-core vs same-kernel V3 control. Same-kernel M4 in
cycles 1-5 was a worst-case contention bound, not a deployment
number — user's "5%/50%" framing was correct.

Cycle 3 MC verdict unchanged (QPU MC contributes ~0.4 under any
contention); cycle 5 CDEF deferred verdict softened to
opportunistic helper (NEON-fallback proxy used since cycle 5
Phase 6 not yet built).

- tests/bench_concurrent_mixed.c (configurable cpu-kernel /
  qpu-kernel matrix; supports MC, LPF4, LPF8, IDCT real QPU
  dispatch; CDEF uses NEON-on-core-3 fallback)
- CMakeLists.txt: build target wired with all FFmpeg + dav1d sources
- docs/issues/003-mixed-kernel-m4-bench.md: closure + matrix
- docs/k3_mc_phase7.md: M4 methodology caveat extended with V3/V4
- docs/k5_cdef_phase3_partial.md: deployment recommendation updated

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
 2026-05-18 13:44:08 +00:00
marfrit 460a6a6d08 Calibration: M4 same-kernel measures worst-case contention 
User-flagged 2026-05-18: the cycles 3 (MC) + 5 (CDEF) 'CPU only'
verdicts were based on M4 measuring same-kernel concurrent NEON+QPU,
which is the WORST case for memory-bandwidth contention. A real
decoder pipeline has CPU doing kernel A + QPU doing kernel B
concurrently — different access patterns contend less.

Concretely: in a real pipeline, CPU runs entropy + MC + other work
while QPU is idle except for IDCT + LPF. The 'opportunistic QPU
helper' for CDEF (or MC) hasn't been measured. M4 set the bar too
high.

Updates:
- docs/k3_mc_phase7.md §'M4 methodology caveat' added with the
  user's contribution framing
- docs/k5_cdef_phase3_partial.md §'Deployment recommendation'
  softened from 'CPU only' to 'CPU baseline; QPU helper viable in
  mixed-kernel deployment, unmeasured'
- docs/issues/003-mixed-kernel-m4-bench.md filed — the rigorous
  test to close the question (4 variants: bandwidth+bandwidth,
  compute+CDEF, same-kernel control, real-pipeline mix)
- ~/.claude/projects/-home-mfritsche-src-daedalus-fourier/memory/
  feedback_m4_same_kernel_worst_case.md added — carries the
  calibration into future cycles + Phase 8 deployment decisions
- MEMORY.md index updated

The bandwidth-bound vs compute-bound classification still holds at
the kernel level — Phase 9 cross-cycle lesson stays valid. But its
mapping to deployment is nuanced:
  - Bandwidth-bound on QPU → DEFINITIVE offload (M4 +ve, cycles 1+2+4)
  - Compute-bound on QPU → OPPORTUNISTIC helper if pipeline has
    bandwidth-light CPU work running concurrently (cycles 3+5,
    needs Issue 003 measurement)

Phase 8 V4L2 wrapper should keep CDEF + MC slot-able to either CPU
or QPU at runtime (not hard-baked), so Issue 003's result can update
the dispatch table without re-architecture.

No code changes. Doc + memory + issue only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
 2026-05-18 13:31:27 +00:00
marfrit 356e446a49 Cycle 3 (MC interpolation) closure: M1'''=100%, R'''=0.067 RED, M4=-19.5% 
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>
 2026-05-18 12:51:43 +00:00