Commit d551e454 authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
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[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: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 575ee714
......@@ -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)
......
......@@ -2637,7 +2637,9 @@ static void tcp_undo_spur_to_response(struct sock *sk, int flag)
* algorithm is not part of the F-RTO detection algorithm
* given in RFC4138 but can be selected separately).
* Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
* and TCP falls back to conventional RTO recovery.
* and TCP falls back to conventional RTO recovery. F-RTO allows overriding
* of Nagle, this is done using frto_counter states 2 and 3, when a new data
* segment of any size sent during F-RTO, state 2 is upgraded to 3.
*
* Rationale: if the RTO was spurious, new ACKs should arrive from the
* original window even after we transmit two new data segments.
......@@ -2666,7 +2668,7 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
inet_csk(sk)->icsk_retransmits = 0;
if (!before(tp->snd_una, tp->frto_highmark)) {
tcp_enter_frto_loss(sk, tp->frto_counter + 1, flag);
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
return 1;
}
......@@ -2692,7 +2694,7 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
return 1;
}
if ((tp->frto_counter == 2) &&
if ((tp->frto_counter >= 2) &&
(!(flag&FLAG_FORWARD_PROGRESS) ||
((flag&FLAG_DATA_SACKED) && !(flag&FLAG_ONLY_ORIG_SACKED)))) {
/* RFC4138 shortcoming (see comment above) */
......@@ -2709,14 +2711,15 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
if (!tcp_send_head(sk) ||
after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
tp->snd_una + tp->snd_wnd)) {
tcp_enter_frto_loss(sk, tp->frto_counter + 1, flag);
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3),
flag);
return 1;
}
tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
tp->frto_counter = 2;
return 1;
} else /* frto_counter == 2 */ {
} else {
switch (sysctl_tcp_frto_response) {
case 2:
tcp_undo_spur_to_response(sk, flag);
......
......@@ -1035,8 +1035,10 @@ static inline int tcp_nagle_test(struct tcp_sock *tp, struct sk_buff *skb,
if (nonagle & TCP_NAGLE_PUSH)
return 1;
/* Don't use the nagle rule for urgent data (or for the final FIN). */
if (tp->urg_mode ||
/* Don't use the nagle rule for urgent data (or for the final FIN).
* Nagle can be ignored during F-RTO too (see RFC4138).
*/
if (tp->urg_mode || (tp->frto_counter == 2) ||
(TCP_SKB_CB(skb)->flags & TCPCB_FLAG_FIN))
return 1;
......
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