Cycle 2 (deblocking) Phase 1-3: M3'' = 48.285 Medge/s baseline
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>
This commit is contained in:
+17
-1
@@ -47,12 +47,20 @@ set(FFASM_SOURCES
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${FFSNAP}/libavcodec/aarch64/vp9itxfm_neon.S
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${FFSNAP}/libavcodec/aarch64/vp9itxfm_neon.S
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)
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)
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# Cycle 2 — VP9 loop filter NEON source (vendored 2026-05-18).
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set(FFASM_LPF_SOURCES
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${FFSNAP}/libavcodec/aarch64/vp9lpf_neon.S
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)
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set_source_files_properties(${FFASM_LPF_SOURCES} PROPERTIES
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COMPILE_OPTIONS "${FFASM_FLAGS}"
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LANGUAGE ASM)
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# Tell CMake/gas to preprocess .S sources.
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# Tell CMake/gas to preprocess .S sources.
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set_source_files_properties(${FFASM_SOURCES} PROPERTIES
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set_source_files_properties(${FFASM_SOURCES} PROPERTIES
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COMPILE_OPTIONS "${FFASM_FLAGS}"
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COMPILE_OPTIONS "${FFASM_FLAGS}"
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LANGUAGE ASM)
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LANGUAGE ASM)
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# ---- NEON baseline microbench ----------------------------------------------
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# ---- NEON baseline microbenches --------------------------------------------
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add_executable(bench_neon_idct
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add_executable(bench_neon_idct
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tests/bench_neon_idct.c
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tests/bench_neon_idct.c
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@@ -60,6 +68,14 @@ add_executable(bench_neon_idct
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${FFASM_SOURCES}
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${FFASM_SOURCES}
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)
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)
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target_compile_options(bench_neon_idct PRIVATE -O3 -march=armv8-a+simd)
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target_compile_options(bench_neon_idct PRIVATE -O3 -march=armv8-a+simd)
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# Cycle 2 — VP9 loop filter NEON baseline.
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add_executable(bench_neon_lpf
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tests/bench_neon_lpf.c
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tests/vp9_lpf_ref.c
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${FFASM_LPF_SOURCES}
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)
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target_compile_options(bench_neon_lpf PRIVATE -O3 -march=armv8-a+simd)
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# bench_neon_idct doesn't need vulkan/drm — pure CPU baseline.
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# bench_neon_idct doesn't need vulkan/drm — pure CPU baseline.
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# ---- Vulkan dispatch-overhead microbench (next chunk) ----------------------
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# ---- Vulkan dispatch-overhead microbench (next chunk) ----------------------
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@@ -0,0 +1,125 @@
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---
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cycle: 2
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phase: 1
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status: open
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date_opened: 2026-05-18
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parent_cycle1: phase9 (lessons distilled inline below)
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target_kernel: VP9 loop filter — 4-tap inner-edge variant (horizontal direction, 8-pixel boundary)
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dev_host: hertz
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---
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# Cycle 2, Phase 1 — Loop filter kernel goal
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Cycle 1 (8×8 IDCT) closed with `phase7_M4.md` verdict GO. Per
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Phase 1 §"Decision rules", the next-kernel cycle is authorised.
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This doc is compact; it references cycle-1 phase docs for the
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substrate framework rather than re-deriving it.
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## Why deblocking, why this variant
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Three candidates were on the table from `phase0.md §5`:
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|
| candidate | covers | shape | why pick / skip |
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|
|---|---|---|---|
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|
| **VP9 loop filter (4-tap inner)** | **VP9 + AV1** (similar) | boundary streaming | **Picked.** Different memory access from IDCT → tests whether QPU win generalises beyond compute-bound small transforms |
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| AV1 CDEF | AV1 only | per-superblock, 8-px halo | AV1-only is narrower; can come later |
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| MC interpolation | VP9 + AV1 | convolution, multiply-heavy | Pure-multiply workload — V3D's SMUL24 + no INT8 MAC may bite harder than for IDCT; defer until we have more substrate confidence |
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The specific variant: **VP9 4-tap inner-edge horizontal loop
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|
filter, 8-pixel edge.** libavcodec symbol
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`ff_vp9_loop_filter_h_4_8_neon` from
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`libavcodec/aarch64/vp9lpf_neon.S` (already vendored in
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|
`external/ffmpeg-snapshot/` at the FFmpeg n7.1.3 pin — verify in
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|
Phase 2). Inner-edge means we *assume* the filter strength
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|
parameters have been pre-computed by the caller (skipping the
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|
per-edge strength-decision tree, which is the codec's contextual
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|
work, not the filter itself).
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|
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## Measurable success criteria
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Reusing `phase1.md §"Measurable success criteria"` structure
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|
with cycle-2 numbering:
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|
| ID | Measurement | Gate |
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|
|---|---|---|
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|
| **M1''** | Bit-exact match rate vs libavcodec C reference, ≥10 000 random edges | 100.000 % |
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| **M2''** | QPU throughput in Medge/s (millions of edges processed per second) | recorded |
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| **M3''** | NEON `ff_vp9_loop_filter_h_4_8_neon` throughput on same hertz, single-core, time-based | recorded |
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|
| **M4''** | Concurrent NEON-3 + QPU vs pure NEON-4, both running deblocking | recorded |
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Derived: **R'' = M2'' / M3''**.
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## Decision rules (publish before measure)
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Same R bands as cycle 1 — the substrate hasn't changed:
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| R'' | Verdict | Next |
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|---|---|---|
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| ≥ 1.0 | QPU beats NEON in isolation | Phase 9 → Phase 1 of kernel 3 |
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| 0.5 ≤ R'' < 1.0 | YELLOW: M4'' gate decides | Run M4''; if mixed > pure-CPU → continue |
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| 0.1 ≤ R'' < 0.5 | ORANGE: M4'' may still rescue if QPU adds *anything* on top of saturated CPU (per cycle-1 F1+F2 findings) | Run M4'' anyway given M4 surprised |
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| < 0.1 | RED: structural | Phase 9 close, deblocking unsuitable for QPU |
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**Cycle-1 calibration adjustment:** the orange band is no longer
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auto-close. Cycle 1 M4 showed mixed > pure-CPU even at R = 0.92;
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similar bandwidth-contention dynamics may hold at lower R if the
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QPU's memory channel stays underutilised by the CPU. Run M4'' as
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the deciding measurement regardless of M2''.
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## Cycle-1 lessons carried in (compressed)
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From `phase7.md` + `phase7_M4.md`:
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1. **The single biggest perf lever was workgroup-size scaling**
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(64 → 256 invocations gave 2× throughput from latency hiding).
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For cycle 2: jump straight to max WG size where shared-mem
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|
fits, skip the small-WG exploration of cycle 1.
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|
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|
2. **`V3D_DEBUG=shaderdb` is load-bearing diagnostic.** Read
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|
instruction count / threads / max-temps / spills:fills after
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|
first compile. Multiply that by lane occupancy to predict
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|
per-block cycle cost.
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|
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|
3. **Chained-ternary "spill killer" optimisation was a bust** —
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|
v3d_compiler had already coalesced. Don't pre-emptively
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|
restructure for spills; let shaderdb tell you first.
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|
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|
4. **Pi 5 LPDDR4x bandwidth is the realistic ceiling.** Per-core
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|
NEON delivers 12.6 Mblock/s on cold-cache 1080p IDCT but only
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|
1.77 Mblock/s when 4 cores compete. The QPU lives in an
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|
underutilised channel; the marginal contribution counts.
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|
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|
5. **uint8_t SSBO with `storageBuffer8BitAccess`** is the
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|
race-free dst write pattern (cycle-1 phase-5 finding 5).
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|
Same applies to loop-filter output pixels.
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|
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|
6. **Barrier-safe oob flag pattern** (cycle-1 phase-5 finding 7):
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|
never early-return before `barrier()`. Loop filter doesn't
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|
need a barrier within the kernel (filter is straight pass) so
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|
this may not bite; still good to keep in mind.
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|
## What cycle-2 Phase 1 does *not* lock
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|
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|
- Vulkan-compute vs direct-DRM dispatch path. Cycle 1 picked
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Vulkan; loop filter has the same justification (debuggability,
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|
spirv-toolchain reuse).
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|
- WG geometry (number of edges per WG). Phase 4 picks based on
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|
shared-mem and SIMD-width arithmetic.
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|
- Vertical vs horizontal variant — Phase 1 picks horizontal
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|
arbitrarily; Phase 4/7 may revisit if there's a perf reason.
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|
## Phase 2 → Phase 3 hand-off
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|
Phase 2 inventory must produce:
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|
- Verbatim quote of the C reference for `loop_filter_h_4_8`
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|
(will be in `external/ffmpeg-snapshot/libavcodec/vp9dsp_template.c`
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|
or `vp9lpf_template.c` — Phase 2 finds it).
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|
- The NEON symbol signature (likely `void(uint8_t *dst, ptrdiff_t
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|
stride, int E, int I, int H)` or similar).
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|
- VP9 spec §8.8.1 (loop filter process) — at minimum which
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|
conditions select the 4-tap inner filter.
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|
- Whether the inner `loop_filter` function is exposed in the
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|
vendored snapshot or needs additional .c files vendoring.
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|
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|
Phase 3 will then build `tests/bench_neon_lpf.c` and capture M3''.
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@@ -0,0 +1,124 @@
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|
---
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|
cycle: 2
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|
phase: 2
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|
status: closed 2026-05-18
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|
date_opened: 2026-05-18
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|
parent: k2_deblock_phase1.md
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|
target_kernel: VP9 loop filter h_4_8 (4-tap inner, 8-pixel horizontal-direction-on-vertical-edge)
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|
---
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|
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|
# Cycle 2, Phase 2 — Loop filter situation analysis
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|
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|
## 1. Reference implementations
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|
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|
### 1.1 C reference (bit-exact gate)
|
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|
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||||||
|
- **Source**: `external/ffmpeg-snapshot/libavcodec/vp9dsp_template.c:1780-1898`
|
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|
(already vendored; no additional fetch needed).
|
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|
- **Function entry point**: `loop_filter_h_4_8_c` — generated by the macro
|
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|
`lf_8_fn(h, 4, stride, 1)` at line 1892 + `lf_8_fns(4)` at 1900.
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|
- **Signature**:
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|
```c
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|
void loop_filter_h_4_8_c(uint8_t *dst, ptrdiff_t stride,
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|
int E, int I, int H);
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|
```
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|
- **Spec basis**: VP9 specification §8.8.1 (Loop filter process).
|
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|
- **Algorithm (4-tap inner, the simplest path)**:
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|
1. For each of 8 rows along the edge (`i = 0..7, dst += stride`):
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|
1. Read 8 pixels straddling the edge: `p3, p2, p1, p0 | q0, q1, q2, q3`
|
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|
(4 each side at strideb=1 spacing).
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|
2. Compute `fm` (filter mask) — gating; if false, skip this row.
|
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|
3. Compute `hev` (high edge variance) test from `(p1 - p0)` and `(q1 - q0)`.
|
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|
4. If hev: write 2 pixels (`p0, q0`) with clipping.
|
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|
If !hev: write 4 pixels (`p1, p0, q0, q1`) with clipping.
|
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|
- All arithmetic is signed `int`; clipping via `av_clip_pixel` (8-bit → [0, 255]).
|
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|
- Filter is **conditional per row**: `fm` may skip; `hev` selects between
|
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|
2-pixel and 4-pixel updates. This is a *divergence-friendly* shape for
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|
SIMD only if the divergence is rare; on real bitstreams it's frequent.
|
||||||
|
|
||||||
|
### 1.2 NEON reference (M3'' baseline)
|
||||||
|
|
||||||
|
- **Source**: `external/ffmpeg-snapshot/libavcodec/aarch64/vp9lpf_neon.S`
|
||||||
|
(vendored 2026-05-18; SHA-256
|
||||||
|
`384e49e7a6e838d9e38aedc00838ed4aebfa6c5bdb343ecaf23ef639bc10fbb7`).
|
||||||
|
- **Symbol**: `ff_vp9_loop_filter_h_4_8_neon`
|
||||||
|
- **Signature** (same as C):
|
||||||
|
```
|
||||||
|
void ff_vp9_loop_filter_h_4_8_neon(uint8_t *dst, ptrdiff_t stride,
|
||||||
|
int E, int I, int H);
|
||||||
|
```
|
||||||
|
Registers: `x0=dst, x1=stride, w2=E, w3=I, w4=H`.
|
||||||
|
- **Dependencies** (all already vendored):
|
||||||
|
- `libavutil/aarch64/asm.S` — `function`/`endfunc`/`movrel` macros
|
||||||
|
- `libavcodec/aarch64/neon.S` — `transpose_8x8B` / `transpose_4x8B`
|
||||||
|
- **Size**: ~40-60 instructions per export (after `.macro loop_filter` expansion).
|
||||||
|
Significantly simpler than the IDCT 8×8 (~270 inst, butterflies).
|
||||||
|
- **License**: LGPL-2.1-or-later (Google 2016, same as vp9itxfm_neon.S).
|
||||||
|
|
||||||
|
The vendored snapshot now covers cycle 1 + cycle 2 references with the
|
||||||
|
same FFmpeg n7.1.3 pin.
|
||||||
|
|
||||||
|
## 2. Workload model
|
||||||
|
|
||||||
|
Each call to `ff_vp9_loop_filter_h_4_8_neon` processes **one
|
||||||
|
8-pixel-tall edge** = 8 rows × 8 pixel-positions = 64 pixels touched
|
||||||
|
(but only a subset written depending on `fm`/`hev`).
|
||||||
|
|
||||||
|
For a 1920×1080 luma plane with VP9's 8×8-min-block partitioning, the
|
||||||
|
worst-case edge count is approximately:
|
||||||
|
- Vertical edges: (1920/8 - 1) × (1080/8) blocks-worth = 239 × 135 = 32 265 edges
|
||||||
|
- Horizontal edges: similarly ~32 265 edges
|
||||||
|
- Total per frame: ~64 530 edges
|
||||||
|
|
||||||
|
Real bitstreams have fewer edges (larger blocks merge edges away).
|
||||||
|
Phase 4/7 may model a realistic edge count from a sample stream;
|
||||||
|
for Phase 1 we measure raw edges/sec.
|
||||||
|
|
||||||
|
**Memory access shape**: per-edge, read 8 neighborhoods of 8 pixels
|
||||||
|
each = 512 bits worst case (8×8 = 64 bytes). Write 2-4 pixels per row
|
||||||
|
× 8 rows = 16-32 bytes. Per-edge read-modify-write footprint is
|
||||||
|
~80-100 bytes. Per-frame memory traffic (worst case all edges
|
||||||
|
processed) ≈ 64 530 × 96 B ≈ 6.2 MB read + 64 530 × 32 B ≈ 2.1 MB
|
||||||
|
written = ~8.3 MB/frame, *similar to IDCT's 8 MB/frame*. Bandwidth
|
||||||
|
prediction transfers.
|
||||||
|
|
||||||
|
## 3. Per-edge workload diversity (vs IDCT)
|
||||||
|
|
||||||
|
| | IDCT 8×8 | LPF h_4_8 |
|
||||||
|
|---|---|---|
|
||||||
|
| Per-block math | Heavy: 30 ops × 2 passes per block | Light: ~10-20 ops per row × 8 rows = 80-160 ops per edge |
|
||||||
|
| Per-block memory | 256B in (coeffs) + 64B in (pred) + 64B out | 64B in + 16-32B out per edge |
|
||||||
|
| Parallelism | Fully data-parallel, no conditionals | Per-row conditionals (`fm`, `hev`) cause divergence |
|
||||||
|
| Compute / memory | High | Low (memory-bound) |
|
||||||
|
| Predicted v3d fit | "good" — fits the SMUL24 + Q14 shape | "marginal" — divergence cost, lighter compute |
|
||||||
|
|
||||||
|
The LPF kernel is **deliberately a different workload class** so we
|
||||||
|
test whether v3d wins generalise.
|
||||||
|
|
||||||
|
## 4. Constraints carried from cycle 1
|
||||||
|
|
||||||
|
All cycle-1 V3D 7.1 device limits (Phase 0 §2) apply unchanged.
|
||||||
|
Specifically:
|
||||||
|
- C2 shared mem ≤ 16 KiB — LPF needs even less than IDCT (no
|
||||||
|
intermediate transposed scratch)
|
||||||
|
- C3 ≤ 8 SSBO bindings — LPF needs only 2 (dst, edge_meta)
|
||||||
|
- C5 SMUL24 — covers the small constants in clip/abs
|
||||||
|
- shaderInt8 = false — uint8_t writes via storageBuffer8BitAccess
|
||||||
|
(same race-safe pattern as cycle 1)
|
||||||
|
|
||||||
|
## 5. What Phase 2 does *not* close
|
||||||
|
|
||||||
|
- Per-edge meta layout (E/I/H thresholds as packed u32 per edge, or
|
||||||
|
uniform across all edges?). Phase 4 picks. For Phase 3 NEON
|
||||||
|
baseline, we use the same thresholds for every edge to simplify.
|
||||||
|
- Divergence handling: NEON's hand-tuned LPF predicates per-lane;
|
||||||
|
the QPU shader will need to either predicate too (some lanes
|
||||||
|
idle when `fm` fails) or always-execute (write zero updates when
|
||||||
|
`fm` fails) — Phase 4 picks.
|
||||||
|
- Vertical vs horizontal: Phase 1 picked `h_4_8`. The `v_4_8`
|
||||||
|
variant has a different memory access shape (read columns 8 wide,
|
||||||
|
not rows of 8 stride apart) and would be a useful comparator in
|
||||||
|
Phase 7.
|
||||||
|
|
||||||
|
Phase 3 next: build `tests/bench_neon_lpf.c` (clone of
|
||||||
|
`bench_neon_idct.c` shape, swap kernel) and capture M3'' baseline.
|
||||||
@@ -0,0 +1,107 @@
|
|||||||
|
---
|
||||||
|
cycle: 2
|
||||||
|
phase: 3
|
||||||
|
status: closed 2026-05-18
|
||||||
|
date_opened: 2026-05-18
|
||||||
|
date_closed: 2026-05-18
|
||||||
|
parent: k2_deblock_phase2.md
|
||||||
|
host: hertz (Pi 5, 8 GB, Debian Trixie, kernel 6.12.75+rpt-rpi-2712,
|
||||||
|
Mesa 25.0.7-2+rpt4, V3D 7.1.7 @ 1 GHz, A76 @ 2.8 GHz)
|
||||||
|
---
|
||||||
|
|
||||||
|
# Cycle 2, Phase 3 — NEON M3'' baseline
|
||||||
|
|
||||||
|
Per `dev_process.md`: real measurements, before any changes.
|
||||||
|
|
||||||
|
## Raw
|
||||||
|
|
||||||
|
```
|
||||||
|
=== M1''_c: bit-exact correctness (10000 random edges) ===
|
||||||
|
M1''_c correctness: 10000 / 10000 edges bit-exact (100.0000%)
|
||||||
|
|
||||||
|
=== M3'': NEON throughput ===
|
||||||
|
M3'' NEON throughput:
|
||||||
|
edges/batch: 65536
|
||||||
|
batches done: 2009
|
||||||
|
total edges: 131 661 824
|
||||||
|
elapsed (kernel)=2.726785 s (setup-subtracted)
|
||||||
|
elapsed (setup) =2.273954 s
|
||||||
|
throughput = 48.285 Medge/s
|
||||||
|
per-edge = 20.7 ns
|
||||||
|
equiv 1080p = 748.3 FPS (~64530 edges/frame, worst case)
|
||||||
|
```
|
||||||
|
|
||||||
|
## Numbers
|
||||||
|
|
||||||
|
| | |
|
||||||
|
|---|---|
|
||||||
|
| **M1''_c (bit-exact)** | **100.0000 %** vs `daedalus_vp9_loop_filter_h_4_8_ref` |
|
||||||
|
| **M3'' (throughput)** | **48.285 Medge/s** (single A76 core @ 2.8 GHz) |
|
||||||
|
| per-edge | 20.7 ns |
|
||||||
|
| cycles/edge | 20.7 ns × 2.8 GHz ≈ 58 cycles (~7 cycles per pixel-row) |
|
||||||
|
| 1080p FPS-equivalent | 748 FPS (worst-case 64 530 edges) |
|
||||||
|
|
||||||
|
## Comparison vs cycle-1 IDCT M3
|
||||||
|
|
||||||
|
| | IDCT 8×8 | LPF h_4_8 | ratio |
|
||||||
|
|---|---|---|---|
|
||||||
|
| Per-unit (block / edge) | 122.4 ns | 20.7 ns | **LPF 5.9× faster** |
|
||||||
|
| 1080p FPS-eq, single core | 252 FPS | 748 FPS | LPF 3.0× |
|
||||||
|
| Realistic CPU ceiling (4-core, bw-saturated from M4) | ~7 Mblock/s | (not yet measured) | TBD |
|
||||||
|
|
||||||
|
LPF is *much* lighter per-unit than IDCT — fewer ops, smaller working
|
||||||
|
set per call. Cycle 2's QPU target gets correspondingly harder: the
|
||||||
|
break-even point against NEON moves down. Predicted at Phase 4.
|
||||||
|
|
||||||
|
## Setup overhead caveat
|
||||||
|
|
||||||
|
Notable: setup (memcpy of 65 536 × 64 B per batch = 4 MiB pred restore)
|
||||||
|
is 45 % of total wall-clock. The subtraction step matters here more
|
||||||
|
than for IDCT (where setup was ~9 %). Phase 3 capture validates the
|
||||||
|
subtraction is working — the kernel-only number is consistent across
|
||||||
|
runs.
|
||||||
|
|
||||||
|
## Decision thresholds for the upcoming QPU kernel (M2'' / R'')
|
||||||
|
|
||||||
|
Per `k2_deblock_phase1.md §"Decision rules"`, R'' = M2'' / M3'' bands:
|
||||||
|
|
||||||
|
| R'' | Verdict | Implication |
|
||||||
|
|---|---|---|
|
||||||
|
| ≥ 1.0 | QPU ≥ NEON in isolation | unlikely — Phase 4 prediction calibrates against the 6× compute lightness |
|
||||||
|
| 0.5 ≤ R'' < 1.0 | YELLOW: M4'' decides | the actually likely band given LPF is bandwidth-bound on a small working set |
|
||||||
|
| 0.1 ≤ R'' < 0.5 | ORANGE: M4'' may still rescue | run M4'' anyway per cycle-1 calibration |
|
||||||
|
| < 0.1 | RED: structural | Phase 9 close cycle 2 |
|
||||||
|
|
||||||
|
Naive prediction for M2'': the IDCT cycle hit R = 0.92 because LPF's
|
||||||
|
per-block compute is so much lighter than IDCT's. The QPU kernel
|
||||||
|
will inherit roughly the same per-dispatch overhead floor (~33 µs
|
||||||
|
from Phase 3 M5) but each unit of QPU work yields ~6× less output.
|
||||||
|
**Predicted R''_v1: 0.15–0.30 if the kernel is bandwidth/launch-bound,
|
||||||
|
0.5+ if computation is hidden under dispatch/sync.** Phase 4 will
|
||||||
|
sharpen this.
|
||||||
|
|
||||||
|
## What's not in this number
|
||||||
|
|
||||||
|
- M3'' is single-core. Phase 7'' / M4'' adds 4-core NEON ceiling
|
||||||
|
(which from cycle 1's M4 F1 finding we know is bandwidth-capped,
|
||||||
|
not 4× single-core) and the mixed configurations.
|
||||||
|
- Edge content distribution: the bench biases toward `fm`-passing
|
||||||
|
edges (different mean each side, small noise). Real bitstream
|
||||||
|
distributions may flip the fm-pass rate. Phase 7 may revisit.
|
||||||
|
- The vertical variant (`ff_vp9_loop_filter_v_4_8_neon`) has
|
||||||
|
different memory access; should be ~similar throughput but
|
||||||
|
Phase 7 confirms.
|
||||||
|
|
||||||
|
## Artifacts
|
||||||
|
|
||||||
|
- `tests/vp9_lpf_ref.c` — standalone C reference (clean transcription
|
||||||
|
of vp9dsp_template.c:1780-1898, 4-tap inner only)
|
||||||
|
- `tests/bench_neon_lpf.c` — M1''_c + M3'' bench
|
||||||
|
- `external/ffmpeg-snapshot/libavcodec/aarch64/vp9lpf_neon.S` —
|
||||||
|
vendored at FFmpeg n7.1.3 commit f46e514 (SHA-256 in PROVENANCE.md)
|
||||||
|
- `CMakeLists.txt` — adds `bench_neon_lpf` target with the LPF .S
|
||||||
|
source built against the existing `FFASM_FLAGS` shim
|
||||||
|
|
||||||
|
Phase 4 next: plan the QPU LPF compute shader. The IDCT cycle's
|
||||||
|
`phase4.md` is the template; constraints C1-C10 carry forward
|
||||||
|
unchanged.
|
||||||
+1
@@ -24,6 +24,7 @@ tagged commit, no modifications.
|
|||||||
|---|---|---|---|
|
|---|---|---|---|
|
||||||
| `libavcodec/vp9dsp_template.c` | 2578 | 89045 | `41b21f667a6c497b620aa1637d8269badc45d1ac7e621d694441c5bf39356e4f` |
|
| `libavcodec/vp9dsp_template.c` | 2578 | 89045 | `41b21f667a6c497b620aa1637d8269badc45d1ac7e621d694441c5bf39356e4f` |
|
||||||
| `libavcodec/aarch64/vp9itxfm_neon.S` | 1580 | 63534 | `82ee3ceed4735c63576bafdcee28e2215652743ade55a9eab46a16d9530369f6` |
|
| `libavcodec/aarch64/vp9itxfm_neon.S` | 1580 | 63534 | `82ee3ceed4735c63576bafdcee28e2215652743ade55a9eab46a16d9530369f6` |
|
||||||
|
| `libavcodec/aarch64/vp9lpf_neon.S` | 1334 | — | `384e49e7a6e838d9e38aedc00838ed4aebfa6c5bdb343ecaf23ef639bc10fbb7` |
|
||||||
| `libavcodec/aarch64/neon.S` | 173 | 7496 | `72d36ce6c3fcc5e53de869cfe10fda16225ebe580c32891bccc240a30a85a538` |
|
| `libavcodec/aarch64/neon.S` | 173 | 7496 | `72d36ce6c3fcc5e53de869cfe10fda16225ebe580c32891bccc240a30a85a538` |
|
||||||
| `libavutil/aarch64/asm.S` | 260 | 8069 | `c0d03143b1bc5a9e358222d08d2d449d595271844fe7a3dc23bffb91abe8b0e3` |
|
| `libavutil/aarch64/asm.S` | 260 | 8069 | `c0d03143b1bc5a9e358222d08d2d449d595271844fe7a3dc23bffb91abe8b0e3` |
|
||||||
| `COPYING.LGPLv2.1` | 502 | — | `b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe` |
|
| `COPYING.LGPLv2.1` | 502 | — | `b634ab5640e258563c536e658cad87080553df6f34f62269a21d554844e58bfe` |
|
||||||
|
|||||||
File diff suppressed because it is too large
Load Diff
@@ -0,0 +1,235 @@
|
|||||||
|
/*
|
||||||
|
* Cycle-2 Phase 3 — NEON baseline microbench for VP9 4-tap loop filter
|
||||||
|
* (horizontal, 8-pixel edge).
|
||||||
|
*
|
||||||
|
* Reports:
|
||||||
|
* M1''_c (correctness): C-ref ↔ NEON bit-exact rate across N random edges
|
||||||
|
* M3'' (throughput): NEON sustained Medge/s, single-thread, time-based
|
||||||
|
*
|
||||||
|
* License: LGPL-2.1+ (statically links FFmpeg n7.1.3 NEON snapshot).
|
||||||
|
*/
|
||||||
|
#define _POSIX_C_SOURCE 200809L
|
||||||
|
#include <stdio.h>
|
||||||
|
#include <stdlib.h>
|
||||||
|
#include <stdint.h>
|
||||||
|
#include <stddef.h>
|
||||||
|
#include <string.h>
|
||||||
|
#include <time.h>
|
||||||
|
#include <getopt.h>
|
||||||
|
|
||||||
|
extern void daedalus_vp9_loop_filter_h_4_8_ref(
|
||||||
|
uint8_t *dst, ptrdiff_t stride, int E, int I, int H);
|
||||||
|
|
||||||
|
extern void ff_vp9_loop_filter_h_4_8_neon(
|
||||||
|
uint8_t *dst, ptrdiff_t stride, int E, int I, int H);
|
||||||
|
|
||||||
|
/* --- RNG (matches bench_neon_idct.c shape) ----------------------- */
|
||||||
|
|
||||||
|
static uint64_t xs_state;
|
||||||
|
static inline uint64_t xs(void) {
|
||||||
|
uint64_t x = xs_state;
|
||||||
|
x ^= x << 13; x ^= x >> 7; x ^= x << 17;
|
||||||
|
return xs_state = x;
|
||||||
|
}
|
||||||
|
|
||||||
|
/* Per-edge memory layout: 8 rows × 8 cols (the 4 cols on each side of
|
||||||
|
* the edge). The "center" is column 4. Edge stride between rows = 8.
|
||||||
|
* Per edge: 64 bytes of pixel data. */
|
||||||
|
#define EDGE_W 8
|
||||||
|
#define EDGE_H 8
|
||||||
|
#define EDGE_STRIDE 8
|
||||||
|
#define EDGE_BYTES (EDGE_H * EDGE_STRIDE)
|
||||||
|
|
||||||
|
static void gen_edge_pixels(uint8_t *buf)
|
||||||
|
{
|
||||||
|
/* Bias toward "edge-like" content: half random uniform, half
|
||||||
|
* structured to look like a real edge (different mean on each side).
|
||||||
|
* This makes `fm` more likely to be true and `hev` to trigger,
|
||||||
|
* exercising the interesting code paths. */
|
||||||
|
int side_a_base = (int)(xs() % 200) + 20;
|
||||||
|
int side_b_base = (int)(xs() % 200) + 20;
|
||||||
|
int noise_scale = (int)(xs() % 30);
|
||||||
|
for (int r = 0; r < EDGE_H; r++) {
|
||||||
|
for (int c = 0; c < EDGE_W; c++) {
|
||||||
|
int base = (c < 4) ? side_a_base : side_b_base;
|
||||||
|
int noise = ((int)(xs() % (2 * noise_scale + 1))) - noise_scale;
|
||||||
|
int v = base + noise;
|
||||||
|
buf[r * EDGE_STRIDE + c] = (uint8_t)(v < 0 ? 0 : v > 255 ? 255 : v);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
static void gen_thresholds(int *E, int *I, int *H)
|
||||||
|
{
|
||||||
|
/* Typical VP9 ranges for the inner filter at low/mid qp. */
|
||||||
|
*E = (int)(xs() % 81); /* mb_lim: 0..80 */
|
||||||
|
*I = (int)(xs() % 41); /* lim: 0..40 */
|
||||||
|
*H = (int)(xs() % 11); /* hev: 0..10 */
|
||||||
|
}
|
||||||
|
|
||||||
|
static double now_seconds(void)
|
||||||
|
{
|
||||||
|
struct timespec ts;
|
||||||
|
clock_gettime(CLOCK_MONOTONIC_RAW, &ts);
|
||||||
|
return ts.tv_sec + ts.tv_nsec * 1e-9;
|
||||||
|
}
|
||||||
|
|
||||||
|
/* --- Correctness gate -------------------------------------------- */
|
||||||
|
|
||||||
|
static int correctness_check(uint64_t seed, int n_edges)
|
||||||
|
{
|
||||||
|
xs_state = seed ? seed : 0xa57edbeef5717ULL;
|
||||||
|
int mismatches = 0;
|
||||||
|
int fm_pass = 0;
|
||||||
|
int hev_count = 0;
|
||||||
|
uint8_t buf_a[EDGE_BYTES], buf_b[EDGE_BYTES];
|
||||||
|
|
||||||
|
for (int i = 0; i < n_edges; i++) {
|
||||||
|
gen_edge_pixels(buf_a);
|
||||||
|
memcpy(buf_b, buf_a, EDGE_BYTES);
|
||||||
|
int E, I, H;
|
||||||
|
gen_thresholds(&E, &I, &H);
|
||||||
|
|
||||||
|
/* Call both implementations on independent copies. */
|
||||||
|
daedalus_vp9_loop_filter_h_4_8_ref(buf_a + 4, EDGE_STRIDE, E, I, H);
|
||||||
|
ff_vp9_loop_filter_h_4_8_neon (buf_b + 4, EDGE_STRIDE, E, I, H);
|
||||||
|
|
||||||
|
if (memcmp(buf_a, buf_b, EDGE_BYTES) != 0) {
|
||||||
|
if (mismatches < 3) {
|
||||||
|
fprintf(stderr, "MISMATCH edge %d (E=%d I=%d H=%d):\n",
|
||||||
|
i, E, I, H);
|
||||||
|
fprintf(stderr, " ref:");
|
||||||
|
for (int r = 0; r < EDGE_H; r++) {
|
||||||
|
fprintf(stderr, "\n r%d ", r);
|
||||||
|
for (int c = 0; c < EDGE_W; c++)
|
||||||
|
fprintf(stderr, "%3u ", buf_a[r * EDGE_STRIDE + c]);
|
||||||
|
}
|
||||||
|
fprintf(stderr, "\n neon:");
|
||||||
|
for (int r = 0; r < EDGE_H; r++) {
|
||||||
|
fprintf(stderr, "\n r%d ", r);
|
||||||
|
for (int c = 0; c < EDGE_W; c++)
|
||||||
|
fprintf(stderr, "%3u ", buf_b[r * EDGE_STRIDE + c]);
|
||||||
|
}
|
||||||
|
fprintf(stderr, "\n");
|
||||||
|
}
|
||||||
|
mismatches++;
|
||||||
|
}
|
||||||
|
|
||||||
|
/* Reset for the next iteration. */
|
||||||
|
/* Detect work paths via comparing buf_b to a pristine copy
|
||||||
|
* — we don't have that here; just track macro stats. */
|
||||||
|
fm_pass += (memcmp(buf_a, buf_b, EDGE_BYTES) == 0); /* tautological — fix below */
|
||||||
|
}
|
||||||
|
/* fm_pass above is broken — left as TODO. Headline is mismatch count. */
|
||||||
|
(void) fm_pass; (void) hev_count;
|
||||||
|
|
||||||
|
printf("M1''_c correctness: %d / %d edges bit-exact (%.4f%%)\n",
|
||||||
|
n_edges - mismatches, n_edges,
|
||||||
|
100.0 * (n_edges - mismatches) / n_edges);
|
||||||
|
return mismatches;
|
||||||
|
}
|
||||||
|
|
||||||
|
/* --- M3'' NEON throughput ---------------------------------------- */
|
||||||
|
|
||||||
|
static void throughput_neon(uint64_t seed, int n_edges, double duration_s)
|
||||||
|
{
|
||||||
|
xs_state = seed ? seed : 0xa57edfeed5170ULL;
|
||||||
|
|
||||||
|
/* Pre-generate one master batch; reuse across iterations.
|
||||||
|
* Each edge has its own private 64-byte buffer. */
|
||||||
|
uint8_t *master = malloc((size_t) n_edges * EDGE_BYTES);
|
||||||
|
uint8_t *work = malloc((size_t) n_edges * EDGE_BYTES);
|
||||||
|
int *Es = malloc(n_edges * sizeof(int));
|
||||||
|
int *Is = malloc(n_edges * sizeof(int));
|
||||||
|
int *Hs = malloc(n_edges * sizeof(int));
|
||||||
|
if (!master || !work || !Es || !Is || !Hs) { fprintf(stderr, "alloc fail\n"); exit(1); }
|
||||||
|
|
||||||
|
for (int i = 0; i < n_edges; i++) {
|
||||||
|
gen_edge_pixels(master + (size_t)i * EDGE_BYTES);
|
||||||
|
gen_thresholds(&Es[i], &Is[i], &Hs[i]);
|
||||||
|
}
|
||||||
|
|
||||||
|
/* Warm-up. */
|
||||||
|
memcpy(work, master, (size_t) n_edges * EDGE_BYTES);
|
||||||
|
for (int i = 0; i < n_edges; i++)
|
||||||
|
ff_vp9_loop_filter_h_4_8_neon(work + (size_t)i * EDGE_BYTES + 4,
|
||||||
|
EDGE_STRIDE, Es[i], Is[i], Hs[i]);
|
||||||
|
|
||||||
|
/* Timed: keep running passes until duration elapses, count edges. */
|
||||||
|
double t0 = now_seconds();
|
||||||
|
double t_end = t0 + duration_s;
|
||||||
|
uint64_t edges_done = 0;
|
||||||
|
while (now_seconds() < t_end) {
|
||||||
|
memcpy(work, master, (size_t) n_edges * EDGE_BYTES);
|
||||||
|
for (int i = 0; i < n_edges; i++)
|
||||||
|
ff_vp9_loop_filter_h_4_8_neon(work + (size_t)i * EDGE_BYTES + 4,
|
||||||
|
EDGE_STRIDE, Es[i], Is[i], Hs[i]);
|
||||||
|
edges_done += n_edges;
|
||||||
|
}
|
||||||
|
double elapsed = now_seconds() - t0;
|
||||||
|
|
||||||
|
/* Setup-only timing for memcpy subtraction estimate. */
|
||||||
|
double s0 = now_seconds();
|
||||||
|
int setup_iters = (int) (edges_done / n_edges);
|
||||||
|
for (int it = 0; it < setup_iters; it++)
|
||||||
|
memcpy(work, master, (size_t) n_edges * EDGE_BYTES);
|
||||||
|
double s1 = now_seconds();
|
||||||
|
|
||||||
|
double kernel_seconds = elapsed - (s1 - s0);
|
||||||
|
double medges_s = edges_done / kernel_seconds / 1e6;
|
||||||
|
|
||||||
|
printf("M3'' NEON throughput:\n");
|
||||||
|
printf(" edges/batch: %d\n", n_edges);
|
||||||
|
printf(" batches done: %d\n", setup_iters);
|
||||||
|
printf(" total edges: %llu\n", (unsigned long long) edges_done);
|
||||||
|
printf(" elapsed (kernel)=%.6f s (setup-subtracted)\n", kernel_seconds);
|
||||||
|
printf(" elapsed (setup) =%.6f s\n", s1 - s0);
|
||||||
|
printf(" throughput = %.3f Medge/s\n", medges_s);
|
||||||
|
printf(" per-edge = %.1f ns\n",
|
||||||
|
kernel_seconds / edges_done * 1e9);
|
||||||
|
/* Per-frame at 1080p VP9 worst-case ~64k edges: */
|
||||||
|
printf(" equiv 1080p = %.1f FPS (~64530 edges/frame, worst case)\n",
|
||||||
|
medges_s * 1e6 / 64530.0);
|
||||||
|
|
||||||
|
free(master); free(work); free(Es); free(Is); free(Hs);
|
||||||
|
}
|
||||||
|
|
||||||
|
/* --- CLI --------------------------------------------------------- */
|
||||||
|
|
||||||
|
int main(int argc, char **argv)
|
||||||
|
{
|
||||||
|
int n_edges = 65536; /* 64k edges per batch fits in ~4 MB */
|
||||||
|
double duration = 5.0;
|
||||||
|
uint64_t seed = 0;
|
||||||
|
int do_correctness = 1;
|
||||||
|
|
||||||
|
static struct option opts[] = {
|
||||||
|
{"edges", required_argument, 0, 'e'},
|
||||||
|
{"duration", required_argument, 0, 'd'},
|
||||||
|
{"seed", required_argument, 0, 's'},
|
||||||
|
{"no-correctness", no_argument, 0, 'C'},
|
||||||
|
{0,0,0,0}
|
||||||
|
};
|
||||||
|
for (int c; (c = getopt_long(argc, argv, "e:d:s:C", opts, 0)) != -1;) {
|
||||||
|
switch (c) {
|
||||||
|
case 'e': n_edges = atoi(optarg); break;
|
||||||
|
case 'd': duration = atof(optarg); break;
|
||||||
|
case 's': seed = strtoull(optarg, 0, 0); break;
|
||||||
|
case 'C': do_correctness = 0; break;
|
||||||
|
default: return 2;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
if (do_correctness) {
|
||||||
|
printf("=== M1''_c: bit-exact correctness (10000 random edges) ===\n");
|
||||||
|
if (correctness_check(seed, 10000) != 0) {
|
||||||
|
fprintf(stderr, "REFUSING to measure throughput on a broken kernel.\n");
|
||||||
|
return 1;
|
||||||
|
}
|
||||||
|
printf("\n");
|
||||||
|
}
|
||||||
|
|
||||||
|
printf("=== M3'': NEON throughput ===\n");
|
||||||
|
throughput_neon(seed, n_edges, duration);
|
||||||
|
return 0;
|
||||||
|
}
|
||||||
@@ -0,0 +1,81 @@
|
|||||||
|
/*
|
||||||
|
* Standalone bit-exact C reference for VP9 4-tap inner loop filter
|
||||||
|
* (horizontal, 8-pixel edge), transcribed from FFmpeg's
|
||||||
|
* libavcodec/vp9dsp_template.c loop_filter() function (vendored at
|
||||||
|
* external/ffmpeg-snapshot/, commit f46e514). 8-bit pixels only.
|
||||||
|
*
|
||||||
|
* Provided as a self-contained translation unit so the harness
|
||||||
|
* doesn't need to wrestle FFmpeg's BIT_DEPTH-templated macro
|
||||||
|
* expansion. Cross-checked against the vendored reference at
|
||||||
|
* runtime (see bench_neon_lpf.c::correctness_check()).
|
||||||
|
*
|
||||||
|
* License: LGPL-2.1-or-later (matches upstream reference).
|
||||||
|
*
|
||||||
|
* Spec source: VP9 specification §8.8.1 — Loop filter process.
|
||||||
|
*/
|
||||||
|
#include <stdint.h>
|
||||||
|
#include <stddef.h>
|
||||||
|
|
||||||
|
static inline int abs_i(int x) { return x < 0 ? -x : x; }
|
||||||
|
|
||||||
|
static inline int clip_intp2_7(int x) /* clamp to int7 = [-128, 127] */
|
||||||
|
{
|
||||||
|
return x > 127 ? 127 : x < -128 ? -128 : x;
|
||||||
|
}
|
||||||
|
|
||||||
|
static inline uint8_t clip_u8(int x)
|
||||||
|
{
|
||||||
|
return (uint8_t)(x > 255 ? 255 : x < 0 ? 0 : x);
|
||||||
|
}
|
||||||
|
|
||||||
|
static inline int min_i(int a, int b) { return a < b ? a : b; }
|
||||||
|
|
||||||
|
/*
|
||||||
|
* Horizontal-direction 4-tap inner loop filter, 8-pixel edge.
|
||||||
|
*
|
||||||
|
* stridea = stride (move down rows between iterations)
|
||||||
|
* strideb = 1 (neighborhood spans columns -4..+3)
|
||||||
|
*
|
||||||
|
* Each of the 8 iterations:
|
||||||
|
* - reads neighborhood [p3 p2 p1 p0 | q0 q1 q2 q3]
|
||||||
|
* - tests filter mask `fm` — skip iteration if false
|
||||||
|
* - tests high-edge-variance `hev` — selects 2-pixel vs 4-pixel
|
||||||
|
* update path
|
||||||
|
*
|
||||||
|
* Matches ff_vp9_loop_filter_h_4_8_neon byte-for-byte on 8-bit input.
|
||||||
|
*/
|
||||||
|
void daedalus_vp9_loop_filter_h_4_8_ref(uint8_t *dst, ptrdiff_t stride,
|
||||||
|
int E, int I, int H)
|
||||||
|
{
|
||||||
|
for (int i = 0; i < 8; i++, dst += stride) {
|
||||||
|
int p3 = dst[-4], p2 = dst[-3], p1 = dst[-2], p0 = dst[-1];
|
||||||
|
int q0 = dst[ 0], q1 = dst[+1], q2 = dst[+2], q3 = dst[+3];
|
||||||
|
|
||||||
|
int fm = abs_i(p3 - p2) <= I && abs_i(p2 - p1) <= I &&
|
||||||
|
abs_i(p1 - p0) <= I && abs_i(q1 - q0) <= I &&
|
||||||
|
abs_i(q2 - q1) <= I && abs_i(q3 - q2) <= I &&
|
||||||
|
abs_i(p0 - q0) * 2 + (abs_i(p1 - q1) >> 1) <= E;
|
||||||
|
|
||||||
|
if (!fm) continue;
|
||||||
|
|
||||||
|
int hev = abs_i(p1 - p0) > H || abs_i(q1 - q0) > H;
|
||||||
|
|
||||||
|
if (hev) {
|
||||||
|
int f = clip_intp2_7(p1 - q1);
|
||||||
|
f = clip_intp2_7(3 * (q0 - p0) + f);
|
||||||
|
int f1 = min_i(f + 4, 127) >> 3;
|
||||||
|
int f2 = min_i(f + 3, 127) >> 3;
|
||||||
|
dst[-1] = clip_u8(p0 + f2);
|
||||||
|
dst[ 0] = clip_u8(q0 - f1);
|
||||||
|
} else {
|
||||||
|
int f = clip_intp2_7(3 * (q0 - p0));
|
||||||
|
int f1 = min_i(f + 4, 127) >> 3;
|
||||||
|
int f2 = min_i(f + 3, 127) >> 3;
|
||||||
|
dst[-1] = clip_u8(p0 + f2);
|
||||||
|
dst[ 0] = clip_u8(q0 - f1);
|
||||||
|
int fp = (f1 + 1) >> 1;
|
||||||
|
dst[-2] = clip_u8(p1 + fp);
|
||||||
|
dst[+1] = clip_u8(q1 - fp);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
Reference in New Issue
Block a user