claude-noether
814b74d0bb
Establishes observable baseline metrics before any daedalus-fourier
kernel substitution lands. Step 1 of the daemon-rewrite arc tracked
at daedalus-v4l2#11.
Changes
-------
- Per-frame `decoder: OK ...` log line now carries decode_us=N (the
send_packet + receive_frame wall-clock cost in microseconds —
exclusively the libavcodec round-trip, not the bitstream pack /
SPS-PPS synth / pack-to-planes work).
- New "decoder stats" summary line every DAEDALUS_STATS_EVERY (60)
decoded frames, reporting: codec, frame count, window seconds,
fps, avg decode_us, MBs/s throughput, bytes/MB bitrate.
Sample
------
decoder stats: codec=h264 frames=300 window=12.32s fps=24.35
avg_decode_us=4216.4 mbs_per_s=87643 bs_b_per_mb=1.56
What this tells us
------------------
Steady-state on higgs (Pi CM5) decoding bbb_720p_h264.mp4:
~4 ms decode_us, ~90 K MBs/s, well under the daedalus-fourier
NEON kernel ceilings (IDCT 4×4 @ 175 Mblocks/s, deblock @ 92 Medges/s,
qpel mc20 @ 131 Mblocks/s — all 100-1000× over our actual workload).
Means the 4 ms/frame is mostly libavcodec's CABAC + MV prediction +
intra prediction overhead, NOT the pixel-math primitives.
Substituting a single primitive would shave only a small slice of
the 4 ms. Useful as guidance for the upcoming substitution work —
we'll pick the primitive with the largest cycle cost relative to
the alternative, and measure CPU saved per substitution.
No behaviour change: counters are static + unsynchronised (the
chardev event loop is single-threaded); reset when codec_id changes.
clock_gettime(CLOCK_MONOTONIC) for timing.
daedalus-v4l2
V4L2 stateless decoder for the Raspberry Pi 5 / CM5, backed by the
daedalus-fourier kernel library (VP9 + AV1 CDEF + H.264 video
decode kernels on VideoCore VII compute + ARM NEON).
Status: scaffold (2026-05-18). Architecture locked per daedalus-fourier session memory; implementation not yet begun.
What this is
Sibling repo to daedalus-fourier (the kernel library; cycles 1-9 closed).
A two-piece userspace + kernel-module stack that exposes a V4L2
stateless decoder interface (/dev/videoNN) so that
libva-v4l2-request-fourier → firefox-fourier /
chromium-fourier can drive it the same way they drive existing
hardware-decode pipelines on Pi 5 / RK3588.
+-----------------------------------------------------------+
| firefox-fourier / chromium-fourier (existing) |
+-----------------------------------------------------------+
| VA-API |
+-----------------------------------------------------------+
| libva-v4l2-request-fourier (existing, sibling project) |
+-----------------------------------------------------------+
| V4L2 stateless ioctl uAPI |
+-----------------------------------------------------------+
| daedalus-v4l2 kernel module (`kernel/`) |
| - registers /dev/videoNN |
| - parses V4L2 stateless ioctls (VP9/AV1/H.264 controls) |
| - forwards bitstream + controls to userspace daemon |
| via chardev or netlink |
+-----------------------------------------------------------+
| daedalus-v4l2 userspace daemon (`daemon/`) |
| - takes bitstream blobs + per-slice controls |
| - drives FFmpeg parsers via dlopen (Option γ) |
| - dispatches per-block ops via daedalus-fourier |
| public API (daedalus_dispatch_*) |
| - posts decoded frames back to kernel module |
+-----------------------------------------------------------+
| daedalus-fourier kernel library (sibling project) |
| - exports include/daedalus.h public API |
| - per-kernel CPU NEON + opportunistic V3D QPU dispatch |
| - 9 closed cycles across VP9, AV1 CDEF, H.264 |
+-----------------------------------------------------------+
| V3D 7.1 (Mesa userspace v3dv) + ARM NEON (BCM2712) |
+-----------------------------------------------------------+
Why this architecture (Option B + γ + sibling)
Locked by user 2026-05-18 from 3 options in
daedalus-fourier/docs/phase8_scoping.md:
- Option B over A (userspace v4l2loopback): real
/dev/videoNN, proper DRM PRIME / dmabuf for browser zero-copy. - Option γ: dlopen FFmpeg as parser at runtime. No vendoring, fastest to v1.
- Sibling repo: per
project_consumer_targetconvention, V4L2-side work lives outside daedalus-fourier so the kernel-library has a clean API boundary.
Status
Initial scaffold only. See docs/architecture.md for the
deeper design and docs/roadmap.md for the
sub-phase breakdown.
Repo layout
kernel/— Linux kernel module (V4L2 device registration + ioctl handling + userspace chardev bridge). Out-of-tree.daemon/— userspace decoder daemon (linkslibdaedalus_core.afrom sibling daedalus-fourier; uses dlopen for FFmpeg parser).include/— shared headers between kernel and daemon.docs/— architecture + roadmap.
License
Kernel module: GPLv2 (required for kernel-tree compatibility). Userspace daemon: BSD-2-Clause (matches daedalus-fourier).