diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 737b32e529561801040fdd3212d5c43ed4ddeae1..0e1da6602e054c24ee3f27f8dfe8b5d288e00c69 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -307,6 +307,21 @@ struct tcp_sock {
 	struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */
 	struct tcp_sack_block selective_acks[4]; /* The SACKS themselves*/
 
+	struct tcp_sack_block recv_sack_cache[4];
+
+	/* from STCP, retrans queue hinting */
+	struct sk_buff* lost_skb_hint;
+
+	struct sk_buff *scoreboard_skb_hint;
+	struct sk_buff *retransmit_skb_hint;
+	struct sk_buff *forward_skb_hint;
+	struct sk_buff *fastpath_skb_hint;
+
+	int     fastpath_cnt_hint;
+	int     lost_cnt_hint;
+	int     retransmit_cnt_hint;
+	int     forward_cnt_hint;
+
 	__u16	advmss;		/* Advertised MSS			*/
 	__u16	prior_ssthresh; /* ssthresh saved at recovery start	*/
 	__u32	lost_out;	/* Lost packets			*/
diff --git a/include/net/sock.h b/include/net/sock.h
index ff13c4cc287add76e658418aaae91970c1c87f66..982b4ecd187b9393b9470a3da7462bdd878a0e52 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1247,6 +1247,12 @@ static inline struct page *sk_stream_alloc_page(struct sock *sk)
 		     (skb != (struct sk_buff *)&(sk)->sk_write_queue);	\
 		     skb = skb->next)
 
+/*from STCP for fast SACK Process*/
+#define sk_stream_for_retrans_queue_from(skb, sk)			\
+		for (; (skb != (sk)->sk_send_head) &&                   \
+		     (skb != (struct sk_buff *)&(sk)->sk_write_queue);	\
+		     skb = skb->next)
+
 /*
  *	Default write policy as shown to user space via poll/select/SIGIO
  */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6e6f0f3f1dd8cff376c20fef44114dc47baad947..0f984801197229c2a3280f7a165cfec233233a63 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1207,6 +1207,15 @@ static inline void tcp_mib_init(void)
 	TCP_ADD_STATS_USER(TCP_MIB_MAXCONN, -1);
 }
 
+/*from STCP */
+static inline void clear_all_retrans_hints(struct tcp_sock *tp){
+	tp->lost_skb_hint = NULL;
+	tp->scoreboard_skb_hint = NULL;
+	tp->retransmit_skb_hint = NULL;
+	tp->forward_skb_hint = NULL;
+	tp->fastpath_skb_hint = NULL;
+}
+
 /* /proc */
 enum tcp_seq_states {
 	TCP_SEQ_STATE_LISTENING,
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 34cfa58eab7667ef3769bb63f0c3288b31b7e327..40a26b7157b49bcbf68530b37f14e80f4fa5c616 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -897,18 +897,32 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 	int prior_fackets;
 	u32 lost_retrans = 0;
 	int flag = 0;
+	int dup_sack = 0;
 	int i;
 
 	if (!tp->sacked_out)
 		tp->fackets_out = 0;
 	prior_fackets = tp->fackets_out;
 
-	for (i=0; i<num_sacks; i++, sp++) {
-		struct sk_buff *skb;
-		__u32 start_seq = ntohl(sp->start_seq);
-		__u32 end_seq = ntohl(sp->end_seq);
-		int fack_count = 0;
-		int dup_sack = 0;
+	/* SACK fastpath:
+	 * if the only SACK change is the increase of the end_seq of
+	 * the first block then only apply that SACK block
+	 * and use retrans queue hinting otherwise slowpath */
+	flag = 1;
+	for (i = 0; i< num_sacks; i++) {
+		__u32 start_seq = ntohl(sp[i].start_seq);
+		__u32 end_seq =	 ntohl(sp[i].end_seq);
+
+		if (i == 0){
+			if (tp->recv_sack_cache[i].start_seq != start_seq)
+				flag = 0;
+		} else {
+			if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
+			    (tp->recv_sack_cache[i].end_seq != end_seq))
+				flag = 0;
+		}
+		tp->recv_sack_cache[i].start_seq = start_seq;
+		tp->recv_sack_cache[i].end_seq = end_seq;
 
 		/* Check for D-SACK. */
 		if (i == 0) {
@@ -940,15 +954,58 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 			if (before(ack, prior_snd_una - tp->max_window))
 				return 0;
 		}
+	}
+
+	if (flag)
+		num_sacks = 1;
+	else {
+		int j;
+		tp->fastpath_skb_hint = NULL;
+
+		/* order SACK blocks to allow in order walk of the retrans queue */
+		for (i = num_sacks-1; i > 0; i--) {
+			for (j = 0; j < i; j++){
+				if (after(ntohl(sp[j].start_seq),
+					  ntohl(sp[j+1].start_seq))){
+					sp[j].start_seq = htonl(tp->recv_sack_cache[j+1].start_seq);
+					sp[j].end_seq = htonl(tp->recv_sack_cache[j+1].end_seq);
+					sp[j+1].start_seq = htonl(tp->recv_sack_cache[j].start_seq);
+					sp[j+1].end_seq = htonl(tp->recv_sack_cache[j].end_seq);
+				}
+
+			}
+		}
+	}
+
+	/* clear flag as used for different purpose in following code */
+	flag = 0;
+
+	for (i=0; i<num_sacks; i++, sp++) {
+		struct sk_buff *skb;
+		__u32 start_seq = ntohl(sp->start_seq);
+		__u32 end_seq = ntohl(sp->end_seq);
+		int fack_count;
+
+		/* Use SACK fastpath hint if valid */
+		if (tp->fastpath_skb_hint) {
+			skb = tp->fastpath_skb_hint;
+			fack_count = tp->fastpath_cnt_hint;
+		} else {
+			skb = sk->sk_write_queue.next;
+			fack_count = 0;
+		}
 
 		/* Event "B" in the comment above. */
 		if (after(end_seq, tp->high_seq))
 			flag |= FLAG_DATA_LOST;
 
-		sk_stream_for_retrans_queue(skb, sk) {
+		sk_stream_for_retrans_queue_from(skb, sk) {
 			int in_sack, pcount;
 			u8 sacked;
 
+			tp->fastpath_skb_hint = skb;
+			tp->fastpath_cnt_hint = fack_count;
+
 			/* The retransmission queue is always in order, so
 			 * we can short-circuit the walk early.
 			 */
@@ -1023,6 +1080,9 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 						TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
 						tp->lost_out -= tcp_skb_pcount(skb);
 						tp->retrans_out -= tcp_skb_pcount(skb);
+
+						/* clear lost hint */
+						tp->retransmit_skb_hint = NULL;
 					}
 				} else {
 					/* New sack for not retransmitted frame,
@@ -1035,6 +1095,9 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 					if (sacked & TCPCB_LOST) {
 						TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
 						tp->lost_out -= tcp_skb_pcount(skb);
+
+						/* clear lost hint */
+						tp->retransmit_skb_hint = NULL;
 					}
 				}
 
@@ -1058,6 +1121,7 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 			    (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
 				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
 				tp->retrans_out -= tcp_skb_pcount(skb);
+				tp->retransmit_skb_hint = NULL;
 			}
 		}
 	}
@@ -1085,6 +1149,9 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
 				tp->retrans_out -= tcp_skb_pcount(skb);
 
+				/* clear lost hint */
+				tp->retransmit_skb_hint = NULL;
+
 				if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 					tp->lost_out += tcp_skb_pcount(skb);
 					TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
@@ -1192,6 +1259,8 @@ static void tcp_enter_frto_loss(struct sock *sk)
 	tcp_set_ca_state(sk, TCP_CA_Loss);
 	tp->high_seq = tp->frto_highmark;
 	TCP_ECN_queue_cwr(tp);
+
+	clear_all_retrans_hints(tp);
 }
 
 void tcp_clear_retrans(struct tcp_sock *tp)
@@ -1258,6 +1327,8 @@ void tcp_enter_loss(struct sock *sk, int how)
 	tcp_set_ca_state(sk, TCP_CA_Loss);
 	tp->high_seq = tp->snd_nxt;
 	TCP_ECN_queue_cwr(tp);
+
+	clear_all_retrans_hints(tp);
 }
 
 static int tcp_check_sack_reneging(struct sock *sk)
@@ -1482,17 +1553,37 @@ static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
 			       int packets, u32 high_seq)
 {
 	struct sk_buff *skb;
-	int cnt = packets;
+	int cnt;
 
-	BUG_TRAP(cnt <= tp->packets_out);
+	BUG_TRAP(packets <= tp->packets_out);
+	if (tp->lost_skb_hint) {
+		skb = tp->lost_skb_hint;
+		cnt = tp->lost_cnt_hint;
+	} else {
+		skb = sk->sk_write_queue.next;
+		cnt = 0;
+	}
 
-	sk_stream_for_retrans_queue(skb, sk) {
-		cnt -= tcp_skb_pcount(skb);
-		if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
+	sk_stream_for_retrans_queue_from(skb, sk) {
+		/* TODO: do this better */
+		/* this is not the most efficient way to do this... */
+		tp->lost_skb_hint = skb;
+		tp->lost_cnt_hint = cnt;
+		cnt += tcp_skb_pcount(skb);
+		if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, high_seq))
 			break;
 		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 			tp->lost_out += tcp_skb_pcount(skb);
+
+			/* clear xmit_retransmit_queue hints
+			 *  if this is beyond hint */
+			if(tp->retransmit_skb_hint != NULL &&
+			   before(TCP_SKB_CB(skb)->seq,
+				  TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) {
+
+				tp->retransmit_skb_hint = NULL;
+			}
 		}
 	}
 	tcp_sync_left_out(tp);
@@ -1519,13 +1610,28 @@ static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
 	if (tcp_head_timedout(sk, tp)) {
 		struct sk_buff *skb;
 
-		sk_stream_for_retrans_queue(skb, sk) {
-			if (tcp_skb_timedout(sk, skb) &&
-			    !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
+		skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
+			: sk->sk_write_queue.next;
+
+		sk_stream_for_retrans_queue_from(skb, sk) {
+			if (!tcp_skb_timedout(sk, skb))
+				break;
+
+			if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
 				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 				tp->lost_out += tcp_skb_pcount(skb);
+
+				/* clear xmit_retrans hint */
+				if (tp->retransmit_skb_hint &&
+				    before(TCP_SKB_CB(skb)->seq,
+					   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
+
+					tp->retransmit_skb_hint = NULL;
 			}
 		}
+
+		tp->scoreboard_skb_hint = skb;
+
 		tcp_sync_left_out(tp);
 	}
 }
@@ -1605,6 +1711,10 @@ static void tcp_undo_cwr(struct sock *sk, const int undo)
 	}
 	tcp_moderate_cwnd(tp);
 	tp->snd_cwnd_stamp = tcp_time_stamp;
+
+	/* There is something screwy going on with the retrans hints after
+	   an undo */
+	clear_all_retrans_hints(tp);
 }
 
 static inline int tcp_may_undo(struct tcp_sock *tp)
@@ -1688,6 +1798,9 @@ static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
 		sk_stream_for_retrans_queue(skb, sk) {
 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
 		}
+
+		clear_all_retrans_hints(tp);
+
 		DBGUNDO(sk, tp, "partial loss");
 		tp->lost_out = 0;
 		tp->left_out = tp->sacked_out;
@@ -2117,6 +2230,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
 		tcp_packets_out_dec(tp, skb);
 		__skb_unlink(skb, &sk->sk_write_queue);
 		sk_stream_free_skb(sk, skb);
+		clear_all_retrans_hints(tp);
 	}
 
 	if (acked&FLAG_ACKED) {
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 602e7057e4383ff100a28fd6489bd843a17ab0d9..029c70dfb585f74e74383faf40c1816b4e6d410d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -436,6 +436,8 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss
 	u16 flags;
 
 	BUG_ON(len > skb->len);
+
+ 	clear_all_retrans_hints(tp);
 	nsize = skb_headlen(skb) - len;
 	if (nsize < 0)
 		nsize = 0;
@@ -1260,7 +1262,10 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int m
 		BUG_ON(tcp_skb_pcount(skb) != 1 ||
 		       tcp_skb_pcount(next_skb) != 1);
 
-		/* Ok.  We will be able to collapse the packet. */
+		/* changing transmit queue under us so clear hints */
+		clear_all_retrans_hints(tp);
+
+		/* Ok.	We will be able to collapse the packet. */
 		__skb_unlink(next_skb, &sk->sk_write_queue);
 
 		memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
@@ -1330,6 +1335,8 @@ void tcp_simple_retransmit(struct sock *sk)
 		}
 	}
 
+	clear_all_retrans_hints(tp);
+
 	if (!lost)
 		return;
 
@@ -1468,13 +1475,25 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
-	int packet_cnt = tp->lost_out;
+	int packet_cnt;
+
+	if (tp->retransmit_skb_hint) {
+		skb = tp->retransmit_skb_hint;
+		packet_cnt = tp->retransmit_cnt_hint;
+	}else{
+		skb = sk->sk_write_queue.next;
+		packet_cnt = 0;
+	}
 
 	/* First pass: retransmit lost packets. */
-	if (packet_cnt) {
-		sk_stream_for_retrans_queue(skb, sk) {
+	if (tp->lost_out) {
+		sk_stream_for_retrans_queue_from(skb, sk) {
 			__u8 sacked = TCP_SKB_CB(skb)->sacked;
 
+			/* we could do better than to assign each time */
+			tp->retransmit_skb_hint = skb;
+			tp->retransmit_cnt_hint = packet_cnt;
+
 			/* Assume this retransmit will generate
 			 * only one packet for congestion window
 			 * calculation purposes.  This works because
@@ -1485,10 +1504,12 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 			if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
 				return;
 
-			if (sacked&TCPCB_LOST) {
+			if (sacked & TCPCB_LOST) {
 				if (!(sacked&(TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
-					if (tcp_retransmit_skb(sk, skb))
+					if (tcp_retransmit_skb(sk, skb)) {
+						tp->retransmit_skb_hint = NULL;
 						return;
+					}
 					if (icsk->icsk_ca_state != TCP_CA_Loss)
 						NET_INC_STATS_BH(LINUX_MIB_TCPFASTRETRANS);
 					else
@@ -1501,8 +1522,8 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 									  TCP_RTO_MAX);
 				}
 
-				packet_cnt -= tcp_skb_pcount(skb);
-				if (packet_cnt <= 0)
+				packet_cnt += tcp_skb_pcount(skb);
+				if (packet_cnt >= tp->lost_out)
 					break;
 			}
 		}
@@ -1528,9 +1549,18 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 	if (tcp_may_send_now(sk, tp))
 		return;
 
-	packet_cnt = 0;
+	if (tp->forward_skb_hint) {
+		skb = tp->forward_skb_hint;
+		packet_cnt = tp->forward_cnt_hint;
+	} else{
+		skb = sk->sk_write_queue.next;
+		packet_cnt = 0;
+	}
+
+	sk_stream_for_retrans_queue_from(skb, sk) {
+		tp->forward_cnt_hint = packet_cnt;
+		tp->forward_skb_hint = skb;
 
-	sk_stream_for_retrans_queue(skb, sk) {
 		/* Similar to the retransmit loop above we
 		 * can pretend that the retransmitted SKB
 		 * we send out here will be composed of one
@@ -1547,8 +1577,10 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 			continue;
 
 		/* Ok, retransmit it. */
-		if (tcp_retransmit_skb(sk, skb))
+		if (tcp_retransmit_skb(sk, skb)) {
+			tp->forward_skb_hint = NULL;
 			break;
+		}
 
 		if (skb == skb_peek(&sk->sk_write_queue))
 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,