tcp: back retransmit_high when it over-estimated

If lost skb is sacked, we might have nothing to retransmit
as high as the retransmit_high is pointing to, so place
it lower to avoid unnecessary walking.

This is mainly for the case where high L'ed skbs gets sacked.

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

1 files changed, 10 insertions, 2 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 239cea7b6c0e..8f9793a37b61 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2035,16 +2035,22 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
         struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb;
         struct sk_buff *hole = NULL;
+        u32 last_lost;
         int mib_idx;
         int fwd_rexmitting = 0;
 
         if (!tp->lost_out)
                 tp->retransmit_high = tp->snd_una;
 
-        if (tp->retransmit_skb_hint)
+        if (tp->retransmit_skb_hint) {
                 skb = tp->retransmit_skb_hint;
-        else
+                last_lost = TCP_SKB_CB(skb)->end_seq;
+                if (after(last_lost, tp->retransmit_high))
+                        last_lost = tp->retransmit_high;
+        } else {
                 skb = tcp_write_queue_head(sk);
+                last_lost = tp->snd_una;
+        }
 
         /* First pass: retransmit lost packets. */
         tcp_for_write_queue_from(skb, sk) {
@@ -2073,6 +2079,7 @@ begin_fwd:
                         mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
 
                 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
+                        tp->retransmit_high = last_lost;
                         if (!tcp_can_forward_retransmit(sk))
                                 break;
                         /* Backtrack if necessary to non-L'ed skb */
@@ -2089,6 +2096,7 @@ begin_fwd:
                         continue;
 
                 } else {
+                        last_lost = TCP_SKB_CB(skb)->end_seq;
                         if (icsk->icsk_ca_state != TCP_CA_Loss)
                                 mib_idx = LINUX_MIB_TCPFASTRETRANS;
                         else