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.
daemon/ — daedalus-v4l2 userspace decoder daemon
Userspace daemon that:
- Connects to the kernel module's chardev
- Receives bitstream + V4L2 control blobs
- Parses bitstream via dlopen'd FFmpeg
- Dispatches per-block work via
daedalus_dispatch_*from siblingdaedalus-fourier - Returns decoded frames to kernel
Status
Scaffold only. Phase 8.3 not yet started.
Build dependencies (planned)
- libdaedalus_core.a from sibling daedalus-fourier (static link)
- FFmpeg dev headers (for AVPacket/AVCodec interface types) + runtime FFmpeg .so (loaded via dlopen)
- libv4l2 (for V4L2 control struct definitions)
- pthread
Build (when implemented)
mkdir build && cd build
cmake .. -DDAEDALUS_FOURIER_DIR=/path/to/daedalus-fourier
make
Layout (planned)
CMakeLists.txtsrc/main.c— event loop, chardev connectionsrc/parser.c— FFmpeg dlopen wrapper + per-codec dispatchsrc/decode_vp9.c,src/decode_av1.c,src/decode_h264.c— per-codec block walkerssrc/frame_io.c— frame allocation, return to kernel
License
BSD-2-Clause (matches daedalus-fourier sibling).
Phase 8.3 starting point
A standalone program that:
- Opens a .ivf or .mp4
- Pulls codec packets via dlopen'd avformat
- Calls dlopen'd avcodec to parse (without decoding)
- Walks the block-level metadata
- Validates output structure
No kernel involvement yet — just confirm the parse path works.