First step of 1 Gbps+ readiness (the whole point of the GF(2^16) Leopard FEC):
make 1 Gbps configurable and its dominant failure mode observable, before the
real transport work (sendmmsg + paced encode|send split) lands.
Investigation (6-way) verdict: we're ~halfway, and it's mostly clamps plus one
real piece of work. The integer/type path, FEC (a 1 Gbps frame is only a few
hundred shards in one GF(2^16) block, far under the 65535 ceiling), AES-GCM
(AES-NI, ~10-25x headroom), and the M1 reassembler bounds (fully derived from
the negotiated FecConfig) are ALL already 1 Gbps-ready and untouched.
This commit (the configurable + observable foundation):
- m3.rs: MAX_BITRATE_KBPS 500_000 -> 2_000_000 (2 Gbps headroom over the 1 Gbps+
target); MAX_PROBE_KBPS 1_000_000 -> 3_000_000 (probe can demonstrate headroom
ABOVE the session cap so a client can confidently pick a 1 Gbps+ bitrate).
- transport/udp.rs: TARGET_SOCKBUF 8 MB -> 32 MB (a multi-MB IDR keyframe burst
no longer fills the buffer); scripts/99-punktfunk-net.conf bumped to match.
- Observability: Transport::send now returns Ok(true|false) (false = WouldBlock
send-buffer drop, previously a silent Ok(())). Session counts these as a new
`packets_send_dropped` stat (distinct from recv-side packets_dropped) — in
Stats, the C ABI PunktfunkStats (header regenerated), a PUNKTFUNK_PERF periodic
wire-Mbps + drop dump in virtual_stream, and the speed-test probe completion
log. This is the dominant 1 Gbps+ loss mode and was invisible.
Loopback-verified: a probe now runs at 1.2 Gbps target (no longer truncated to
1 Gbps) with the drop counter live. NOT yet a sustained-1-Gbps proof — the
single-send()-per-packet native path is the next, real piece of work (port the
proven GameStream sendmmsg + paced send thread into the core Transport).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The host warns when its UDP socket-buffer grant is small (Linux caps SO_SNDBUF at
net.core.wmem_max, ~208 KB by default). Validated zero-loss at 5K even at that cap,
but raising it gives send-side headroom for higher bitrates / concurrent sessions.
Referenced from the headless-Steam appliance setup. macOS clients need no tuning.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler