From 5bd081b90b0efbc0f2b45f544e41127661d969fe Mon Sep 17 00:00:00 2001
From: Ben Cartwright-Cox <ben@benjojo.co.uk>
Date: Fri, 13 Oct 2023 12:18:51 +0100
Subject: [PATCH] Add switch to disable TCP_NODELAY

This in an attempt quell CPU usage, since PCCW is having issues when
their {N} number of routers all start RTR sessions at the same time.

A `perf` of the system suggests all of the CPU is going to sending
TCP traffic, and since golang enables NO_DELAY (infamously?) by
default, this is a good smoking gun, since this would imply that
stayrtr is sending 1 TCP packet per RTR PDU, something that would
indeed cause a lot of CPU usage in aggergate!
---
 lib/server.go | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/server.go b/lib/server.go
index 48a8858..05f9755 100644
--- a/lib/server.go
+++ b/lib/server.go
@@ -536,8 +536,16 @@ func (s *Server) Start(bind string) error {
 
 var DisableBGPSec = flag.Bool("disable.bgpsec", false, "Disable sending out BGPSEC Router Keys")
 var DisableASPA = flag.Bool("disable.aspa", false, "Disable sending out ASPA objects")
+var EnableNODELAY = flag.Bool("enable.nodelay", false, "Force enable TCP NODELAY (Likely increases CPU)")
 
 func (s *Server) acceptClientTCP(tcpconn net.Conn) error {
+	if !*EnableNODELAY {
+		tc, ok := tcpconn.(*net.TCPConn)
+		if ok {
+			tc.SetNoDelay(false)
+		}
+	}
+
 	client := ClientFromConn(tcpconn, s, s)
 	client.log = s.log
 	if s.enforceVersion {