From 3eba841bb697fe952d962728d09e558e15e8f5be Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Fri, 27 Nov 2015 17:59:38 +0200
Subject: [PATCH] Use deferred accept in reuseport.Listener. This should reduce
 the number of context switches for busy servers accepting a lot of new
 connections per second. Will test it, since google says TCP_DEFER_ACCEPT
 option is useless :)

---
 reuseport/reuseport.go       |  5 +++++
 reuseport/reuseport_bsd.go   |  8 ++++++--
 reuseport/reuseport_linux.go | 10 ++++++++++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/reuseport/reuseport.go b/reuseport/reuseport.go
index ee33f7d..69d861a 100644
--- a/reuseport/reuseport.go
+++ b/reuseport/reuseport.go
@@ -72,6 +72,11 @@ func Listen(network, addr string) (l net.Listener, err error) {
 		return nil, &ErrNoReusePort{err}
 	}
 
+	if err = setTCPDeferAccept(fd); err != nil {
+		syscall.Close(fd)
+		return nil, err
+	}
+
 	if err = syscall.Bind(fd, sockaddr); err != nil {
 		syscall.Close(fd)
 		return nil, err
diff --git a/reuseport/reuseport_bsd.go b/reuseport/reuseport_bsd.go
index 89b44cb..f9cca96 100644
--- a/reuseport/reuseport_bsd.go
+++ b/reuseport/reuseport_bsd.go
@@ -2,6 +2,10 @@
 
 package reuseport
 
-import "syscall"
-
 var reusePort = syscall.SO_REUSEPORT
+
+func setTCPDeferAccept(fd int) error {
+	// BSD supports similar SO_ACCEPTFILTER option, but I have no access
+	// to BSD at the moment for proper implementation.
+	return nil
+}
diff --git a/reuseport/reuseport_linux.go b/reuseport/reuseport_linux.go
index 483aba1..c7f31db 100644
--- a/reuseport/reuseport_linux.go
+++ b/reuseport/reuseport_linux.go
@@ -1,3 +1,13 @@
+// +build linux
+
 package reuseport
 
+import (
+	"syscall"
+)
+
 var reusePort = 0x0F
+
+func setTCPDeferAccept(fd int) error {
+	return syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.TCP_DEFER_ACCEPT, 2)
+}