From d551e4541dd60ae53459f77a971f2d6043431f5f Mon Sep 17 00:00:00 2001 From: =?utf8?q?Ilpo=20J=C3=A4rvinen?= Date: Mon, 30 Apr 2007 00:42:20 -0700 Subject: [PATCH] [TCP] FRTO: RFC4138 allows Nagle override when new data must be sent MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: David S. Miller --- include/net/tcp.h | 5 +++++ net/ipv4/tcp_input.c | 13 ++++++++----- net/ipv4/tcp_output.c | 6 ++++-- 3 files changed, 17 insertions(+), 7 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index c6ecd455ed..ef8f9d4dae 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) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 6b669898b1..7641b2761a 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -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); diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index b5fa3c19af..0faacf9c41 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -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; -- 2.39.5