From 60647a2f8c704a18701819ec2cc609847b32121b Mon Sep 17 00:00:00 2001
From: Peter Johnson <johnson.peter@gmail.com>
Date: Wed, 9 Dec 2015 00:58:06 -0800
Subject: [PATCH] Turn off Nagle algorithm to decrease latency.

This is safe because of the way writes are performed: for each transmission,
all outgoing messages are concatenated in memory and only a single write()
syscall is made.
---
 src/NetworkConnection.cpp      | 3 +++
 src/tcpsockets/NetworkStream.h | 1 +
 src/tcpsockets/TCPStream.cpp   | 6 ++++++
 src/tcpsockets/TCPStream.h     | 1 +
 4 files changed, 11 insertions(+)

diff --git a/src/NetworkConnection.cpp b/src/NetworkConnection.cpp
index 743f399b17..b2b741eb6d 100644
--- a/src/NetworkConnection.cpp
+++ b/src/NetworkConnection.cpp
@@ -32,6 +32,9 @@ NetworkConnection::NetworkConnection(std::unique_ptr<NetworkStream> stream,
   m_proto_rev = 0x0300;
   m_state = static_cast<int>(kCreated);
   m_last_update = 0;
+
+  // turn off Nagle algorithm; we bundle packets for transmission
+  m_stream->setNoDelay();
 }
 
 NetworkConnection::~NetworkConnection() { Stop(); }
diff --git a/src/tcpsockets/NetworkStream.h b/src/tcpsockets/NetworkStream.h
index 3803796586..63aedb4f2f 100644
--- a/src/tcpsockets/NetworkStream.h
+++ b/src/tcpsockets/NetworkStream.h
@@ -30,6 +30,7 @@ class NetworkStream {
 
   virtual llvm::StringRef getPeerIP() const = 0;
   virtual int getPeerPort() const = 0;
+  virtual void setNoDelay() = 0;
 
   NetworkStream(const NetworkStream&) = delete;
   NetworkStream& operator=(const NetworkStream&) = delete;
diff --git a/src/tcpsockets/TCPStream.cpp b/src/tcpsockets/TCPStream.cpp
index 2fcee36da3..3149be6f55 100644
--- a/src/tcpsockets/TCPStream.cpp
+++ b/src/tcpsockets/TCPStream.cpp
@@ -27,6 +27,7 @@
 #include <WinSock2.h>
 #else
 #include <arpa/inet.h>
+#include <netinet/tcp.h>
 #include <unistd.h>
 #endif
 
@@ -136,6 +137,11 @@ llvm::StringRef TCPStream::getPeerIP() const { return m_peerIP; }
 
 int TCPStream::getPeerPort() const { return m_peerPort; }
 
+void TCPStream::setNoDelay() {
+  int optval = 1;
+  setsockopt(m_sd, IPPROTO_TCP, TCP_NODELAY, (char*)&optval, sizeof optval);
+}
+
 bool TCPStream::WaitForReadEvent(int timeout) {
   fd_set sdset;
   struct timeval tv;
diff --git a/src/tcpsockets/TCPStream.h b/src/tcpsockets/TCPStream.h
index a64df3ef6a..21ef6fdbed 100644
--- a/src/tcpsockets/TCPStream.h
+++ b/src/tcpsockets/TCPStream.h
@@ -53,6 +53,7 @@ class TCPStream : public NetworkStream {
 
   llvm::StringRef getPeerIP() const override;
   int getPeerPort() const override;
+  void setNoDelay() override;
 
   TCPStream(const TCPStream& stream) = delete;
   TCPStream& operator=(const TCPStream&) = delete;