From 986a8b3fb332e04f24f1a652b503bde5e37737dc Mon Sep 17 00:00:00 2001
From: Thomas Sanchez <thomas.sanchz@gmail.com>
Date: Sat, 31 Aug 2013 16:57:08 +0200
Subject: [PATCH 1/2] Add method to get the RTT kernel estimation

---
 service/connection_handler.h |  3 +++
 service/transport.cc         | 17 +++++++++++++++++
 service/transport.h          |  3 +++
 3 files changed, 23 insertions(+)

diff --git a/service/connection_handler.h b/service/connection_handler.h
index 409af51e..01dff5fc 100644
--- a/service/connection_handler.h
+++ b/service/connection_handler.h
@@ -177,6 +177,9 @@ struct ConnectionHandler {
         return *transport_;
     }
 
+    virtual double getEstimatedRTT()
+    { return transport().getEstimatedRTT(); }
+
     const TransportBase & transport() const
     {
         if (!transport_)
diff --git a/service/transport.cc b/service/transport.cc
index 0f26cfc3..0f32075f 100644
--- a/service/transport.cc
+++ b/service/transport.cc
@@ -19,6 +19,7 @@
 #include <sys/epoll.h>
 #include <sys/timerfd.h>
 #include <sys/eventfd.h>
+#include <linux/tcp.h>
 #include <poll.h>
 
 
@@ -1026,5 +1027,21 @@ closePeer()
     return peer().close();
 }
 
+double
+SocketTransport::getEstimatedRTT()
+{
+    tcp_info tcpinfo;
+    int len = sizeof(tcpinfo);
+
+    int success = peer().get_option(IPPROTO_TCP, TCP_INFO, &tcpinfo, &len);
+    if (success != -1) {
+        // usec -> msec
+        return tcpinfo.tcpi_rtt / double(1000);
+    } else {
+        return double(-1);
+    }
+}
+
+
 } // namespace Datacratic
 
diff --git a/service/transport.h b/service/transport.h
index f56bc93b..8fcec054 100644
--- a/service/transport.h
+++ b/service/transport.h
@@ -58,6 +58,8 @@ struct TransportBase : public std::enable_shared_from_this<TransportBase> {
     virtual int handleAsync(const boost::function<void ()> & callback,
                             const char * name, Date dateSet);
 
+    virtual double getEstimatedRTT() { return double(-1);}
+
     virtual ssize_t send(const char * buf, size_t len, int flags) = 0;
     virtual ssize_t recv(char * buf, size_t buf_size, int flags) = 0;
 
@@ -604,6 +606,7 @@ struct SocketTransport
     virtual ssize_t send(const char * buf, size_t len, int flags);
     virtual ssize_t recv(char * buf, size_t buf_size, int flags);
     virtual int closePeer();
+    virtual double getEstimatedRTT();
 
     ACE_SOCK_Stream & peer() { return peer_; }
     const ACE_SOCK_Stream & peer() const { return peer_; }

From 068042224be5b3e81dbe418d91d52af5ed1f45b3 Mon Sep 17 00:00:00 2001
From: Thomas Sanchez <thomas.sanchz@gmail.com>
Date: Sat, 31 Aug 2013 17:50:22 +0200
Subject: [PATCH 2/2] Add safety levels to RTT

---
 service/transport.cc | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/service/transport.cc b/service/transport.cc
index 0f32075f..1b9d5546 100644
--- a/service/transport.cc
+++ b/service/transport.cc
@@ -21,6 +21,7 @@
 #include <sys/eventfd.h>
 #include <linux/tcp.h>
 #include <poll.h>
+#include <chrono>
 
 
 using namespace std;
@@ -1035,8 +1036,18 @@ SocketTransport::getEstimatedRTT()
 
     int success = peer().get_option(IPPROTO_TCP, TCP_INFO, &tcpinfo, &len);
     if (success != -1) {
-        // usec -> msec
-        return tcpinfo.tcpi_rtt / double(1000);
+
+        std::chrono::milliseconds rtt     = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::microseconds(tcpinfo.tcpi_rtt));
+        std::chrono::milliseconds rtt_var = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::microseconds(tcpinfo.tcpi_rttvar));
+
+        /*
+         * As discussed on the ML:
+         * We could also add some 'safety' levels to account for user-level
+         * overhead and weird values that could be returned from this i.e.
+         * rtt = tcp_rtt+3 * var_rtt + 2ms clamp to range (2ms, 50ms)
+         */
+        return rtt.count() + 3 * rtt_var.count() + 2;
+
     } else {
         return double(-1);
     }