[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>

1 files changed, 8 insertions, 4 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f46d24b8410f..cbb83acd830a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -687,7 +687,7 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, unsigned int mss
 
         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 @@ 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);
 
-                /* 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 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb, int m
 
                 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);
         }
 }