[TCP] FRTO: RFC4138 allows Nagle override when new data must be sent

This is a corner case where less than MSS sized new data thingie
is awaiting in the send queue. For F-RTO to work correctly, a
new data segment must be sent at certain point or F-RTO cannot
be used at all. RFC4138 allows overriding of Nagle at that
point.

Implementation uses frto_counter states 2 and 3 to distinguish
when Nagle override is needed.

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

1 files changed, 5 insertions, 0 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index c6ecd455edab..ef8f9d4dae85 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1199,9 +1199,14 @@ static inline struct sk_buff *tcp_send_head(struct sock *sk)
 
 static inline void tcp_advance_send_head(struct sock *sk, struct sk_buff *skb)
 {
+        struct tcp_sock *tp = tcp_sk(sk);
+
         sk->sk_send_head = skb->next;
         if (sk->sk_send_head == (struct sk_buff *)&sk->sk_write_queue)
                 sk->sk_send_head = NULL;
+        /* Don't override Nagle indefinately with F-RTO */
+        if (tp->frto_counter == 2)
+                tp->frto_counter = 3;
 }
 
 static inline void tcp_check_send_head(struct sock *sk, struct sk_buff *skb_unlinked)