rto_restart.patch

From 600a91cce0611400411a08e9ee3e83d503f5a017 Mon Sep 17 00:00:00 2001
From: Mohammad Rajiullah <mrshammi@gmail.com>
Date: Wed, 13 Feb 2013 17:47:16 +0100
Subject: [PATCH] To support rtorestart functionalities.

---
 net/ipv4/tcp_input.c |   33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 18f97ca..8acd086 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3083,6 +3083,19 @@ static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 	tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
 }
 
+/* Find the timestamp of the packet in the write queue head 
+ *  return the diffrence between now and the send time 
+ */
+static unsigned int get_T_earliest(struct sock *sk) 
+{
+	struct timespec now, then, T_earliest;
+	       
+	getnstimeofday(&now);
+	then = ktime_to_timespec(tcp_write_queue_head(sk)->tstamp);
+	T_earliest = timespec_sub(now, then);
+	return timespec_to_jiffies(&T_earliest);
+}
+
 /* Restart timer after forward progress on connection.
  * RFC2988 recommends to restart timer to now+rto.
  */
@@ -3111,6 +3124,26 @@ void tcp_rearm_rto(struct sock *sk)
 			if (delta > 0)
 				rto = delta;
 		}
+                 /* Modified RTO:
+                 * (1) Given an ACK that acknowledges new data and if the 
+                 *     number of outstanding segments is less than four      
+                 * (2) then if the following two conditions hold:                  
+                 *   (a) there is no unsent data ready for transmission
+                 *   OR
+                 *   (b) the receiver's advertised window does not permit 
+                 *       transmission. then:
+                 * (3) set T_earliest to the time elapsed since the earliest
+                 *   outstanding segment was sent and deduct this value from 
+                 *   the rto.
+                 */
+	
+	 	 else if(tp->packets_out < 4 && 
+                         inet_csk(sk)->icsk_pending==ICSK_TIME_RETRANS)// (1)
+			if (sk->sk_send_head == NULL ||                // (2a)
+			    tp->snd_wnd < sk->sk_send_head->len){      // (2b)                                
+			 	unsigned int T_earliest = get_T_earliest(sk);
+                             	rto = rto- T_earliest;                 // (3)
+            		}
 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
 					  TCP_RTO_MAX);
 	}
-- 
1.7.10.4