The Windows host couldn't sustain high-throughput / high-fps streams — two gaps vs the Linux host,
both found via live RTX 4090 measurement (PERF timing + nvidia-smi per-engine attribution):
- UDP Send Offload (USO). punktfunk-core's UdpTransport sent one packet per `send` syscall on
Windows (send_batch/send_gso were Linux-only), capping throughput at high packet rates. Add a
Windows `send_gso` override using `WSASendMsg` + `UDP_SEND_MSG_SIZE` (the Windows analogue of
Linux UDP GSO) via windows-sys — one syscall segments a coalesced <=512-segment super-buffer to
the connected peer. On by default with auto-fallback (PUNKTFUNK_GSO=0 disables, error latches
off); plugs into the existing paced send path. SO_SNDBUF (32MB) was already cross-platform.
- NVENC 2-way split-frame encoding. A single Ada NVENC session tops out ~0.8 Gpix/s, so 5K@240
(1.77 Gpix/s) took ~8 ms/frame -> a ~125 fps ceiling at high motion (the in-game stutter). Set
NV_ENC_INITIALIZE_PARAMS.splitEncodeMode = TWO_FORCED above ~1 Gpix/s (matching the Linux
libavcodec split_encode_mode path) to use both 4090 encoders — measured ~8 ms -> ~4 ms/frame at
throughput. Env override PUNKTFUNK_SPLIT_ENCODE; init-failure fallback disables it (e.g. H264).
Windows-only paths; Linux/macOS unaffected. Builds clean on x86_64-pc-windows-msvc.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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