try using a simpler FIFO order for each backpressure buffer, since there are other mechanisms to penalize the flooding node, leads to better TCP throughput without affecting traffic between other nodes (does affect traffic in the same session, but there's hypothetically workarounds to that)

src/yggdrasil/tcp.go

@@ -246,19 +246,13 @@ func (iface *tcpInterface) handler(sock net.Conn, incoming bool) {
 	defer close(out)
 	go func() {
 		// This goroutine waits for outgoing packets, link protocol traffic, or sends idle keep-alive traffic
-		send := make(chan []byte)
-		defer close(send)
-		go func() {
-			// This goroutine does the actual socket write operations
-			// The parent goroutine aggregates things for it and feeds them in
-			for msg := range send {
-				msgLen := wire_encode_uint64(uint64(len(msg)))
-				buf := net.Buffers{tcp_msg[:], msgLen, msg}
-				buf.WriteTo(sock)
-				atomic.AddUint64(&p.bytesSent, uint64(len(tcp_msg)+len(msgLen)+len(msg)))
-				util_putBytes(msg)
-			}
-		}()
+		send := func(msg []byte) {
+			msgLen := wire_encode_uint64(uint64(len(msg)))
+			buf := net.Buffers{tcp_msg[:], msgLen, msg}
+			buf.WriteTo(sock)
+			atomic.AddUint64(&p.bytesSent, uint64(len(tcp_msg)+len(msgLen)+len(msg)))
+			util_putBytes(msg)
+		}
 		timerInterval := tcp_timeout * 2 / 3
 		timer := time.NewTimer(timerInterval)
 		defer timer.Stop()
@@ -266,7 +260,7 @@ func (iface *tcpInterface) handler(sock net.Conn, incoming bool) {
 			select {
 			case msg := <-p.linkOut:
 				// Always send outgoing link traffic first, if needed
-				send <- msg
+				send(msg)
 				continue
 			default:
 			}
@@ -279,14 +273,14 @@ func (iface *tcpInterface) handler(sock net.Conn, incoming bool) {
 			timer.Reset(timerInterval)
 			select {
 			case _ = <-timer.C:
-				send <- nil // TCP keep-alive traffic
+				send(nil) // TCP keep-alive traffic
 			case msg := <-p.linkOut:
-				send <- msg
+				send(msg)
 			case msg, ok := <-out:
 				if !ok {
 					return
 				}
-				send <- msg // Block until the socket writer has the packet
+				send(msg) // Block until the socket write has finished
 				// Now inform the switch that we're ready for more traffic
 				p.core.switchTable.idleIn <- p.port
 			}