tcp: reduce spurious retransmits due to transient SACK reneging

[pandora-kernel.git] / net / ipv4 / tcp_input.c

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7832d94..6a29845 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1904,16 +1904,17 @@ void tcp_clear_retrans(struct tcp_sock *tp)
        tp->sacked_out = 0;
 }
 
-/* Enter Loss state. If "how" is not zero, forget all SACK information
+/* Enter Loss state. If we detect SACK reneging, forget all SACK information
  * and reset tags completely, otherwise preserve SACKs. If receiver
  * dropped its ofo queue, we will know this due to reneging detection.
  */
-void tcp_enter_loss(struct sock *sk, int how)
+void tcp_enter_loss(struct sock *sk)
 {
        const struct inet_connection_sock *icsk = inet_csk(sk);
        struct tcp_sock *tp = tcp_sk(sk);
        struct sk_buff *skb;
        bool new_recovery = false;
+       bool is_reneg;                  /* is receiver reneging on SACKs? */
 
        /* Reduce ssthresh if it has not yet been made inside this window. */
        if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
@@ -1934,7 +1935,11 @@ void tcp_enter_loss(struct sock *sk, int how)
                tcp_reset_reno_sack(tp);
 
        tp->undo_marker = tp->snd_una;
-       if (how) {
+
+       skb = tcp_write_queue_head(sk);
+       is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
+       if (is_reneg) {
+               NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
                tp->sacked_out = 0;
                tp->fackets_out = 0;
        }
@@ -1948,7 +1953,7 @@ void tcp_enter_loss(struct sock *sk, int how)
                        tp->undo_marker = 0;
 
                TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
-               if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
+               if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
                        TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
                        tp->lost_out += tcp_skb_pcount(skb);
@@ -1981,19 +1986,21 @@ void tcp_enter_loss(struct sock *sk, int how)
  * remembered SACKs do not reflect real state of receiver i.e.
  * receiver _host_ is heavily congested (or buggy).
  *
- * Do processing similar to RTO timeout.
+ * To avoid big spurious retransmission bursts due to transient SACK
+ * scoreboard oddities that look like reneging, we give the receiver a
+ * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
+ * restore sanity to the SACK scoreboard. If the apparent reneging
+ * persists until this RTO then we'll clear the SACK scoreboard.
  */
 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
 {
        if (flag & FLAG_SACK_RENEGING) {
-               struct inet_connection_sock *icsk = inet_csk(sk);
-               NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
+               struct tcp_sock *tp = tcp_sk(sk);
+               unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
+                                         msecs_to_jiffies(10));
 
-               tcp_enter_loss(sk, 1);
-               icsk->icsk_retransmits++;
-               tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-                                         icsk->icsk_rto, TCP_RTO_MAX);
+                                         delay, TCP_RTO_MAX);
                return true;
        }
        return false;