NetworkPerformanceSystem

For groups playing together across long distances. If your friends are 200ms+ away and the game feels like mush no matter how much bandwidth everyone has, this is aimed at you.

Why this is different from the other networking mods

Every other Valheim networking mod treats multiplayer performance as a bandwidth problem — compression, bigger buffers, higher send rates, filtered broadcasts. That is the right diagnosis for ten people in one base saturating a shared cap.

It does not explain why two friends on opposite sides of the world feel awful at 5% link utilisation. Two things in vanilla punish distance specifically, and neither is about bandwidth:

1. The send window is a fixed 10 KB of in-flight data. Throughput through a fixed window is window ÷ round-trip-time, so vanilla's window is correctly sized up to about 67ms and starves everything past it — roughly 41 KB/s at 250ms, no matter how fast your connection is. And it fails hard rather than gracefully: over the limit, that player receives nothing that tick. That is the freeze half of freeze-then-teleport.

2. Simulation authority is handed out by arrival order. Valheim gives each object to one peer to simulate, and everyone else sees it relayed through the host. Vanilla picks whoever happens to be first in an internal list — uncorrelated with who is fighting the creature and uncorrelated with latency. For a spread-out group that is close to the worst available choice, and it is why a mob can feel laggy to everyone at once.

This mod sizes the window per peer from measured round-trip time, and places authority to minimise how stale things look to the people actually watching. Notably, sizing by RTT is a no-op for players who were already fine — simply raising the constant for everybody, which is what the other mods do, hands a 20ms player tens of kilobytes of standing queue, which is latency added to someone who did not have a problem.

What it does

Installing

Server-only works. Vanilla clients get the send window, ownership, and scheduler fixes with nothing installed on their end.

Installing on clients too adds latency compensation and live position reporting for those clients. Mixed groups are fine — benefits are per-player, and a client without the mod behaves exactly as vanilla. There is no version lock: nobody gets kicked for not having it.

Works on dedicated servers and on player-hosted games.

Known limitations

• On a dedicated server, contested objects go to the lowest-latency player present rather than to the server itself - except in the zones the server has actually loaded, which are the ones around the world origin. There, whenever two or more players are present, the server wins contested objects (it is zero hops from everyone, so that is the lowest possible staleness) and simulates them. That is intended and is a CPU cost to plan for on a busy spawn hub; set Allow Host As Owner to false to place purely on players. The server never takes ownership of zones it has not loaded, because owning something it is not simulating would freeze it.
• Latency compensation is dead reckoning: an entity that stops abruptly will overshoot slightly and settle back. Lower LatencyCompensationStrength if you find it distracting; 0 disables it.
• Requires the Steam backend. Crossplay/PlayFab connections do not report round-trip time, and without a measurement every mechanism falls back to vanilla behaviour rather than guessing.
• If the log shows RttSampling disabled, the server's Steam interface could not be queried and everything runs as vanilla; nps_stats shows the reason.
• Honest send windows mean a full server can actually use its bandwidth: 50 players at the default 150 KB/s target is ~60 Mbit/s of upload worst case. Backpressure degrades gracefully if the link is smaller, but provision the server's uplink for the player count rather than assuming vanilla's artificially starved usage.
• On large servers the two knobs that matter are Frame Budget Ms (how much of each server frame the send path may use - under load the per-peer send rate degrades gracefully instead of the frame time growing without bound; nps_stats shows the effective rate) and Max Reassigns Per Pass, which auto-scales with player count so ownership converges at the same per-player rate on a full server as in a small group. The Load Penalty Ms setting spreads contested objects across low-latency peers instead of piling everything on the single lowest-ping player - leave it on unless you specifically want pure staleness placement.
• Max Players raises vanilla's cap of 10, but a crossplay server cannot go past 128 whatever it is set to - PlayFab's lobbies do not hold more, and crossplay clients join that lobby before the server ever sees them. Steam-only servers have no such ceiling. Crossplay (PlayFab) peers also never report a round-trip time, so they are priced at Unmeasured Peer RTT Ms for ownership and rendered at vanilla by other clients.
• Connection Timeout Seconds is for players who get dropped mid-join or during a hitch on a weak link. It does not make a slow connection faster — it stops both ends declaring it dead while it is still working — and it is not free: a player who is genuinely gone now holds their slot, and keeps ownership of everything they were simulating, for that long instead of 30 seconds, and objects an absent owner holds do not move. Size it to the worst connection you actually want to keep. The one timeout a server cannot set for a client is Connect Timeout Seconds, which covers the handshake before anything has been synced — whoever cannot get connected has to raise that one themselves.
• Raising Max Players is not free and nothing here makes it free: each added player costs the host upload and CPU against every other player. Frame Budget Ms and the Steam transport ceiling below are what decide whether a bigger number is actually playable - read the two bullets above before setting one.

Incompatible with

Other networking mods that rewrite the same code: FiresGhettoNetworking, VBNetTweaks, SkadiNet, BetterNetworking, Smoothbrain's Network, NetworkTweaks, WarheimNetwork, TimeoutLimit. BepInEx will refuse to load this mod alongside them rather than leave you half-patched. TimeoutLimit in particular is no longer something you give up: the Connection Timeout settings cover the same ground, and unlike a timeout raised at one layer only, they move both of the places vanilla times out at.

Verified compatible (different layers, no overlap): LeanNet, Compress, Scenic. ReturnToSender is fine too — it already fixes the scheduler, so that one mechanism stands down and the rest keeps working. EnRoute and BetterZeeRouter are fine in the same way: both rework the routed-RPC relay, so the relay-filtering mechanism stands down when either is present and everything else keeps working.

Changelog

See CHANGELOG.md.