commit b76892051cf1c04d95872838e70146f65e3b9d75
author Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Thu Sep 20 11:37:19 2007 -0700
committer David S. Miller <davem@sunset.davemloft.net> Wed Oct 10 16:52:12 2007 -0700
tree 475050b8e41eb317144465b1e2b9255fbad188b4
parent c96fd3d461fa495400df24be3b3b66f0e0b152f9

[TCP]: Avoid clearing sacktag hint in trivial situations

There's no reason to clear the sacktag skb hint when small part
of the rexmit queue changes. Account changes (if any) instead when
fragmenting/collapsing. RTO/FRTO do not touch SACKED_ACKED bits so
no need to discard SACK tag hint at all.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

diff --git a/include/net/tcp.h b/include/net/tcp.h
index d78ad9b..456983d 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1067,11 +1067,15 @@
 }
 
 /* from STCP */
-static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp) {
+static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp) {
 	tp->lost_skb_hint = NULL;
 	tp->scoreboard_skb_hint = NULL;
 	tp->retransmit_skb_hint = NULL;
 	tp->forward_skb_hint = NULL;
+}
+
+static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp) {
+	tcp_clear_retrans_hints_partial(tp);
 	tp->fastpath_skb_hint = NULL;
 }
 

net/ipv4/tcp_input.c

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 65b9f27..4c10d9c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1671,7 +1671,7 @@
 	tp->high_seq = tp->frto_highmark;
 	TCP_ECN_queue_cwr(tp);
 
-	tcp_clear_all_retrans_hints(tp);
+	tcp_clear_retrans_hints_partial(tp);
 }
 
 void tcp_clear_retrans(struct tcp_sock *tp)
@@ -1711,10 +1711,14 @@
 	tp->bytes_acked = 0;
 	tcp_clear_retrans(tp);
 
-	/* Push undo marker, if it was plain RTO and nothing
-	 * was retransmitted. */
-	if (!how)
+	if (!how) {
+		/* Push undo marker, if it was plain RTO and nothing
+		 * was retransmitted. */
 		tp->undo_marker = tp->snd_una;
+		tcp_clear_retrans_hints_partial(tp);
+	} else {
+		tcp_clear_all_retrans_hints(tp);
+	}
 
 	tcp_for_write_queue(skb, sk) {
 		if (skb == tcp_send_head(sk))
@@ -1741,8 +1745,6 @@
 	TCP_ECN_queue_cwr(tp);
 	/* Abort FRTO algorithm if one is in progress */
 	tp->frto_counter = 0;
-
-	tcp_clear_all_retrans_hints(tp);
 }
 
 static int tcp_check_sack_reneging(struct sock *sk)

net/ipv4/tcp_output.c

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f46d24b..cbb83ac 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -687,7 +687,7 @@
 
 	BUG_ON(len > skb->len);
 
-	tcp_clear_all_retrans_hints(tp);
+	tcp_clear_retrans_hints_partial(tp);
 	nsize = skb_headlen(skb) - len;
 	if (nsize < 0)
 		nsize = 0;
@@ -1718,9 +1718,6 @@
 		BUG_ON(tcp_skb_pcount(skb) != 1 ||
 		       tcp_skb_pcount(next_skb) != 1);
 
-		/* changing transmit queue under us so clear hints */
-		tcp_clear_all_retrans_hints(tp);
-
 		/* Ok.	We will be able to collapse the packet. */
 		tcp_unlink_write_queue(next_skb, sk);
 
@@ -1759,6 +1756,13 @@
 
 		tcp_adjust_fackets_out(tp, skb, tcp_skb_pcount(next_skb));
 		tp->packets_out -= tcp_skb_pcount(next_skb);
+
+		/* changed transmit queue under us so clear hints */
+		tcp_clear_retrans_hints_partial(tp);
+		/* manually tune sacktag skb hint */
+		if (tp->fastpath_skb_hint == next_skb)
+			tp->fastpath_skb_hint = skb;
+
 		sk_stream_free_skb(sk, next_skb);
 	}
 }