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feat(core): scale the receive path to the new multi-Gbps ceiling

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- REPLAY_WINDOW 32768 -> 131072: the anti-replay bitmap covered the
  120 ms loss window only to ~2 Gbps; the client now delivers ~4.8 Gbps
  wire, where a late-but-valid Wi-Fi-retried datagram would have been
  dropped as 'older than the window' — false loss. 16 KiB/session
  covers ~12 Gbps.
- RECV_BATCH 32 -> 128: syscall rate stays ~3.4k/s at 430k pkt/s and
  each pump iteration drains the kernel buffer deeper (ring 64->256 KB,
  client sessions only). flush_backlog's iteration cap rescaled to keep
  its ~190 MB guard equivalent.
- PUNKTFUNK_GSO gate is now value-aware: '=0' used to ENABLE GSO on
  Linux (presence check) while disabling Windows USO. GSO stays OPT-IN,
  deliberately: A/B'd twice today — it cuts send-thread CPU ~30% but
  its 16-packet line-rate trains cost delivered throughput on a
  constrained fabric (2.5GbE-hop pair: peak 2453 -> 1908 Mbps and 0.4%
  loss at a rate sendmmsg carries clean). Flipping the default belongs
  with pace-aware chunk spacing (plan Phase 1.2/1.3). docs-site row
  corrected to match.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Enrico Bühler
2026-07-14 19:22:40 +02:00
parent 160914c48b
commit 1a559e8d5e
4 changed files with 28 additions and 16 deletions
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docs-site/content/docs/configuration.md
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@@ -138,7 +138,7 @@ notes for context.
| Setting | Values | Meaning |
|---|---|---|
| `PUNKTFUNK_GSO` | `1` · `0` | UDP Generic Segmentation Offload on the send path (coalesce a frame's packets into kernel super-buffers) — the dominant lever above ~1 Gbps. On by default; auto-falls back to `sendmmsg`. Set `0` if a NIC/middlebox mishandles GSO. |
| `PUNKTFUNK_GSO` | `1` · `0` | UDP Generic Segmentation Offload on the send path (coalesce a frame's packets into kernel super-buffers) — cuts send CPU ~30%, but its line-rate packet trains can cost delivered throughput on constrained links (measured on a 2.5GbE hop). Off by default until send pacing spaces the super-buffers; set `1` to opt in (auto-falls back to `sendmmsg` on kernels/paths without support). |
| `PUNKTFUNK_SPLIT_ENCODE` | `0`/`disable` · `1`/`auto` · `2` · `3` | NVENC N-way split-encode for very high pixel rates (5K@240). `auto` picks automatically above ~1 Gpix/s. |
| `PUNKTFUNK_GPU_PRIORITY_CLASS` | `off` · `normal` · `high` · `realtime` | **(Windows)** GPU scheduling priority for capture/encode under a GPU-saturating game. Default `high`; `realtime` is the strongest lever but can freeze NVENC on some setups. |
| `PUNKTFUNK_IDD_DEPTH` | `N` (default `2`) | **(Windows)** IDD-push pipeline depth. `1` cuts latency once GPU priority is raised; higher smooths a contended GPU. |