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wgengine/userspace: reduce wgLock contention for large peer sets

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Reduces wgLock hold time in maybeReconfigWireguardLocked for nodes
with large peer counts. The reconfig path holds wgLock while
iterating all peers, starving RoutineReadFromTUN and dropping packets
under churn.

Move SetPeers outside wgLock — it holds its own mutex and doesn't
need wgLock. Also fixes SetPeers being called with the previous
config's peer list rather than the incoming one.

Skip updateActivityMapsLocked rebuild when the tracked peer set
hasn't changed.

Signed-off-by: Raj Singh <raj@tailscale.com>
This commit is contained in:
Raj Singh 2026-04-14 21:05:09 -05:00
parent effbe67fe3
commit ade9cf15c2
1 changed files with 16 additions and 2 deletions
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18
wgengine/userspace.go
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@ -141,6 +141,8 @@ type userspaceEngine struct {
lastEngineInputs *maybeReconfigInputs
lastDNSConfig dns.ConfigView // or invalid if none
lastIsSubnetRouter bool // was the node a primary subnet router in the last run.
lastTrackNodes []key.NodePublic // trackNodes from the last updateActivityMapsLocked call
lastTrackIPs []netip.Addr // trackIPs from the last updateActivityMapsLocked call
recvActivityAt map[key.NodePublic]mono.Time
trimmedNodes map[key.NodePublic]bool // set of node keys of peers currently excluded from wireguard config
sentActivityAt map[netip.Addr]*mono.Time // value is accessed atomically
@ -854,7 +856,6 @@ func (e *userspaceEngine) maybeReconfigWireguardLocked(discoChanged map[key.Node
}
full := e.lastCfgFull
e.wgLogger.SetPeers(full.Peers)
// Compute a minimal config to pass to wireguard-go
// based on the full config. Prune off all the peers
@ -973,9 +974,18 @@ func (e *userspaceEngine) updateActivityMapsLocked(trackNodes []key.NodePublic,
if !buildfeatures.HasLazyWG {
return
}
// Skip the map rebuild if the set of tracked keys hasn't changed;
// the maps and activity funcs from the previous call are still valid.
if e.lastTrackNodes != nil && slices.Equal(e.lastTrackNodes, trackNodes) && slices.Equal(e.lastTrackIPs, trackIPs) {
return
}
e.lastTrackNodes = slices.Clone(trackNodes)
e.lastTrackIPs = slices.Clone(trackIPs)
// Generate the new map of which nodekeys we want to track
// receive times for.
mr := map[key.NodePublic]mono.Time{} // TODO: only recreate this if set of keys changed
mr := map[key.NodePublic]mono.Time{}
for _, nk := range trackNodes {
// Preserve old times in the new map, but also
// populate map entries for new trackNodes values with
@ -1086,6 +1096,10 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
e.isLocalAddr.Store(ipset.NewContainsIPFunc(views.SliceOf(routerCfg.LocalAddrs)))
// SetPeers is safe for concurrent use; call before wgLock to avoid
// holding the lock during the O(n) formatting pass.
e.wgLogger.SetPeers(cfg.Peers)
e.wgLock.Lock()
defer e.wgLock.Unlock()
e.tundev.SetWGConfig(cfg)