examples: set socket buffers and raise tun tx_queue (#1928)

* examples: set socket buffers and raise tun tx_queue

* examples: use the default tcp max window for socket buffers

* examples: note buffers are linux only, clarify tx_queue default

* tun: default tx_queue to 5000

examples/config.yml

@@ -135,12 +135,12 @@ listen:
   # superpacket, so the receive scratch is batch * 64KiB per listening socket (~4MiB per routine at the
   # default of 64). Lower this to trade peak per-syscall throughput for memory on constrained hosts.
   #batch: 64
-  # Configure socket buffers for the udp side (outside), leave unset to use the system defaults. Values will be doubled by the kernel
+  # Linux only. Configure socket buffers for the udp side (outside), leave unset to use the system defaults. Values will be doubled by the kernel
   # Default is net.core.rmem_default and net.core.wmem_default (/proc/sys/net/core/rmem_default and /proc/sys/net/core/rmem_default)
   # Maximum is limited by memory in the system, SO_RCVBUFFORCE and SO_SNDBUFFORCE is used to avoid having to raise the system wide
   # max, net.core.rmem_max and net.core.wmem_max
-  #read_buffer: 10485760
-  #write_buffer: 10485760
+  read_buffer: 3412512
+  write_buffer: 3412512
 
   # On Windows only
   # When true, Nebula installs a WFP (Windows Filtering Platform) PERMIT filter scoped to UDP at the listener port.
@@ -262,8 +262,8 @@ tun:
   drop_local_broadcast: false
   # Toggles forwarding of multicast packets
   drop_multicast: false
-  # Sets the transmit queue length, if you notice lots of transmit drops on the tun it may help to raise this number. Default is 500
-  tx_queue: 500
+  # Sets the transmit queue length, if you notice lots of transmit drops on the tun it may help to raise this number. Default is 5000
+  tx_queue: 5000
   # Default MTU for every packet, safe setting is (and the default) 1300 for internet based traffic
   # Anything above 8937, here or on a route below, is capped to 8937 with a warning
   mtu: 1300

overlay/tun.go

@@ -43,7 +43,7 @@ type DeviceFactory func(c *config.C, l *slog.Logger, vpnNetworks []netip.Prefix,
 func NewDeviceFromConfig(c *config.C, l *slog.Logger, vpnNetworks []netip.Prefix, routines int) (Device, error) {
 	switch {
 	case c.GetBool("tun.disabled", false):
-		tun := newDisabledTun(vpnNetworks, c.GetInt("tun.tx_queue", 500), c.GetBool("stats.message_metrics", false), l)
+		tun := newDisabledTun(vpnNetworks, c.GetInt("tun.tx_queue", 5000), c.GetBool("stats.message_metrics", false), l)
 		return tun, nil
 
 	default:

overlay/tun_linux.go

@@ -221,7 +221,7 @@ func newTunGeneric(c *config.C, l *slog.Logger, fd int, vnetHdr bool, offloadFla
 		vnetHdr:                   vnetHdr,
 		offloadFlags:              offloadFlags,
 		vpnNetworks:               vpnNetworks,
-		TXQueueLen:                c.GetInt("tun.tx_queue", 500),
+		TXQueueLen:                c.GetInt("tun.tx_queue", 5000),
 		useSystemRoutes:           c.GetBool("tun.use_system_route_table", false),
 		useSystemRoutesBufferSize: c.GetInt("tun.use_system_route_table_buffer_size", 0),
 		routesFromSystem:          map[netip.Prefix]routing.Gateways{},