| Message ID | 4A950B7F.6000702@tvk.rwth-aachen.de |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 26 Aug 2009, Damian Lukowski wrote: > Here, an ICMP host/network unreachable message, whose payload fits to > TCP's SND.UNA, is taken as an indication that the RTO retransmission has > not been lost due to congestion, but because of a route failure > somewhere along the path. > With true congestion, a router won't trigger such a message and the > patched TCP will operate as standard TCP. > > This patch reverts one RTO backoff, if an ICMP host/network unreachable > message, whose payload fits to TCP's SND.UNA, arrives. > Based on the new RTO, the retransmission timer is reset to reflect the > remaining time, or - if the revert clocked out the timer - a retransmission > is sent out immediately. > Backoffs are only reverted, if TCP is in RTO loss recovery, i.e. if > there have been retransmissions and reversible backoffs, already. > > Changes from v2: > 1) Renaming of skb in tcp_v4_err() moved to another patch. > 2) Reintroduced tcp_bound_rto() and __tcp_set_rto(). > 3) Fixed code comments. > > Signed-off-by: Damian Lukowski <damian@tvk.rwth-aachen.de> > --- > include/net/tcp.h | 12 ++++++++++++ > net/ipv4/tcp_input.c | 5 ++--- > net/ipv4/tcp_ipv4.c | 37 +++++++++++++++++++++++++++++++++++++ > net/ipv4/tcp_timer.c | 2 +- > 4 files changed, 52 insertions(+), 4 deletions(-) > > diff --git a/include/net/tcp.h b/include/net/tcp.h > index 88af843..c35b329 100644 > --- a/include/net/tcp.h > +++ b/include/net/tcp.h > @@ -469,6 +469,7 @@ extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, > int nonagle); > extern int tcp_may_send_now(struct sock *sk); > extern int tcp_retransmit_skb(struct sock *, struct sk_buff *); > +extern void tcp_retransmit_timer(struct sock *sk); > extern void tcp_xmit_retransmit_queue(struct sock *); > extern void tcp_simple_retransmit(struct sock *); > extern int tcp_trim_head(struct sock *, struct sk_buff *, u32); > @@ -521,6 +522,17 @@ extern int tcp_mtu_to_mss(struct sock *sk, int pmtu); > extern int tcp_mss_to_mtu(struct sock *sk, int mss); > extern void tcp_mtup_init(struct sock *sk); > > +static inline void tcp_bound_rto(const struct sock *sk) > +{ > + if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX) > + inet_csk(sk)->icsk_rto = TCP_RTO_MAX; > +} > + > +static inline u32 __tcp_set_rto(const struct tcp_sock *tp) > +{ > + return (tp->srtt >> 3) + tp->rttvar; > +} > + > static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd) > { > tp->pred_flags = htonl((tp->tcp_header_len << 26) | > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index 2bdb0da..af6d6fa 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -685,7 +685,7 @@ static inline void tcp_set_rto(struct sock *sk) > * is invisible. Actually, Linux-2.4 also generates erratic > * ACKs in some circumstances. > */ > - inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar; > + inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); > > /* 2. Fixups made earlier cannot be right. > * If we do not estimate RTO correctly without them, > @@ -696,8 +696,7 @@ static inline void tcp_set_rto(struct sock *sk) > /* NOTE: clamping at TCP_RTO_MIN is not required, current algo > * guarantees that rto is higher. > */ > - if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX) > - inet_csk(sk)->icsk_rto = TCP_RTO_MAX; > + tcp_bound_rto(sk); > } > > /* Save metrics learned by this TCP session. > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c > index 6ca1bc8..6755e29 100644 > --- a/net/ipv4/tcp_ipv4.c > +++ b/net/ipv4/tcp_ipv4.c > @@ -332,12 +332,15 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) > { > struct iphdr *iph = (struct iphdr *)icmp_skb->data; > struct tcphdr *th = (struct tcphdr *)(icmp_skb->data + (iph->ihl << 2)); > + struct inet_connection_sock *icsk; > struct tcp_sock *tp; > struct inet_sock *inet; > const int type = icmp_hdr(icmp_skb)->type; > const int code = icmp_hdr(icmp_skb)->code; > struct sock *sk; > + struct sk_buff *skb; > __u32 seq; > + __u32 remaining; > int err; > struct net *net = dev_net(icmp_skb->dev); > > @@ -367,6 +370,7 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) > if (sk->sk_state == TCP_CLOSE) > goto out; > > + icsk = inet_csk(sk); > tp = tcp_sk(sk); > seq = ntohl(th->seq); > if (sk->sk_state != TCP_LISTEN && > @@ -393,6 +397,39 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) > } > > err = icmp_err_convert[code].errno; > + /* check if icmp_skb allows revert of backoff > + * (see draft-zimmermann-tcp-lcd) */ > + if (code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH) > + break; > + if (seq != tp->snd_una || !icsk->icsk_retransmits || > + !icsk->icsk_backoff) > + break; > + > + icsk->icsk_backoff--; > + inet_csk(sk)->icsk_rto = __tcp_set_rto(tp) << > + icsk->icsk_backoff; > + tcp_bound_rto(sk); > + > + skb = tcp_write_queue_head(sk); > + BUG_ON(!skb); > + > + remaining = icsk->icsk_rto - min(icsk->icsk_rto, > + tcp_time_stamp - TCP_SKB_CB(skb)->when); > + > + if (remaining) { > + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, > + remaining, TCP_RTO_MAX); > + } else if (sock_owned_by_user(sk)) { > + /* RTO revert clocked out retransmission, > + * but socket is locked. Will defer. */ > + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, > + HZ/20, TCP_RTO_MAX); > + } else { > + /* RTO revert clocked out retransmission. > + * Will retransmit now */ > + tcp_retransmit_timer(sk); > + } > + > break; > case ICMP_TIME_EXCEEDED: > err = EHOSTUNREACH; > diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c > index b144a26..a3ba494 100644 > --- a/net/ipv4/tcp_timer.c > +++ b/net/ipv4/tcp_timer.c > @@ -279,7 +279,7 @@ static void tcp_probe_timer(struct sock *sk) > * The TCP retransmit timer. > */ > > -static void tcp_retransmit_timer(struct sock *sk) > +void tcp_retransmit_timer(struct sock *sk) > { > struct tcp_sock *tp = tcp_sk(sk); > struct inet_connection_sock *icsk = inet_csk(sk); > Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
diff --git a/include/net/tcp.h b/include/net/tcp.h index 88af843..c35b329 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -469,6 +469,7 @@ extern void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, int nonagle); extern int tcp_may_send_now(struct sock *sk); extern int tcp_retransmit_skb(struct sock *, struct sk_buff *); +extern void tcp_retransmit_timer(struct sock *sk); extern void tcp_xmit_retransmit_queue(struct sock *); extern void tcp_simple_retransmit(struct sock *); extern int tcp_trim_head(struct sock *, struct sk_buff *, u32); @@ -521,6 +522,17 @@ extern int tcp_mtu_to_mss(struct sock *sk, int pmtu); extern int tcp_mss_to_mtu(struct sock *sk, int mss); extern void tcp_mtup_init(struct sock *sk); +static inline void tcp_bound_rto(const struct sock *sk) +{ + if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX) + inet_csk(sk)->icsk_rto = TCP_RTO_MAX; +} + +static inline u32 __tcp_set_rto(const struct tcp_sock *tp) +{ + return (tp->srtt >> 3) + tp->rttvar; +} + static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd) { tp->pred_flags = htonl((tp->tcp_header_len << 26) | diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 2bdb0da..af6d6fa 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -685,7 +685,7 @@ static inline void tcp_set_rto(struct sock *sk) * is invisible. Actually, Linux-2.4 also generates erratic * ACKs in some circumstances. */ - inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar; + inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); /* 2. Fixups made earlier cannot be right. * If we do not estimate RTO correctly without them, @@ -696,8 +696,7 @@ static inline void tcp_set_rto(struct sock *sk) /* NOTE: clamping at TCP_RTO_MIN is not required, current algo * guarantees that rto is higher. */ - if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX) - inet_csk(sk)->icsk_rto = TCP_RTO_MAX; + tcp_bound_rto(sk); } /* Save metrics learned by this TCP session. diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 6ca1bc8..6755e29 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -332,12 +332,15 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) { struct iphdr *iph = (struct iphdr *)icmp_skb->data; struct tcphdr *th = (struct tcphdr *)(icmp_skb->data + (iph->ihl << 2)); + struct inet_connection_sock *icsk; struct tcp_sock *tp; struct inet_sock *inet; const int type = icmp_hdr(icmp_skb)->type; const int code = icmp_hdr(icmp_skb)->code; struct sock *sk; + struct sk_buff *skb; __u32 seq; + __u32 remaining; int err; struct net *net = dev_net(icmp_skb->dev); @@ -367,6 +370,7 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) if (sk->sk_state == TCP_CLOSE) goto out; + icsk = inet_csk(sk); tp = tcp_sk(sk); seq = ntohl(th->seq); if (sk->sk_state != TCP_LISTEN && @@ -393,6 +397,39 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info) } err = icmp_err_convert[code].errno; + /* check if icmp_skb allows revert of backoff + * (see draft-zimmermann-tcp-lcd) */ + if (code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH) + break; + if (seq != tp->snd_una || !icsk->icsk_retransmits || + !icsk->icsk_backoff) + break; + + icsk->icsk_backoff--; + inet_csk(sk)->icsk_rto = __tcp_set_rto(tp) << + icsk->icsk_backoff; + tcp_bound_rto(sk); + + skb = tcp_write_queue_head(sk); + BUG_ON(!skb); + + remaining = icsk->icsk_rto - min(icsk->icsk_rto, + tcp_time_stamp - TCP_SKB_CB(skb)->when); + + if (remaining) { + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, + remaining, TCP_RTO_MAX); + } else if (sock_owned_by_user(sk)) { + /* RTO revert clocked out retransmission, + * but socket is locked. Will defer. */ + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, + HZ/20, TCP_RTO_MAX); + } else { + /* RTO revert clocked out retransmission. + * Will retransmit now */ + tcp_retransmit_timer(sk); + } + break; case ICMP_TIME_EXCEEDED: err = EHOSTUNREACH; diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index b144a26..a3ba494 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -279,7 +279,7 @@ static void tcp_probe_timer(struct sock *sk) * The TCP retransmit timer. */ -static void tcp_retransmit_timer(struct sock *sk) +void tcp_retransmit_timer(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk);
Here, an ICMP host/network unreachable message, whose payload fits to TCP's SND.UNA, is taken as an indication that the RTO retransmission has not been lost due to congestion, but because of a route failure somewhere along the path. With true congestion, a router won't trigger such a message and the patched TCP will operate as standard TCP. This patch reverts one RTO backoff, if an ICMP host/network unreachable message, whose payload fits to TCP's SND.UNA, arrives. Based on the new RTO, the retransmission timer is reset to reflect the remaining time, or - if the revert clocked out the timer - a retransmission is sent out immediately. Backoffs are only reverted, if TCP is in RTO loss recovery, i.e. if there have been retransmissions and reversible backoffs, already. Changes from v2: 1) Renaming of skb in tcp_v4_err() moved to another patch. 2) Reintroduced tcp_bound_rto() and __tcp_set_rto(). 3) Fixed code comments. Signed-off-by: Damian Lukowski <damian@tvk.rwth-aachen.de> --- include/net/tcp.h | 12 ++++++++++++ net/ipv4/tcp_input.c | 5 ++--- net/ipv4/tcp_ipv4.c | 37 +++++++++++++++++++++++++++++++++++++ net/ipv4/tcp_timer.c | 2 +- 4 files changed, 52 insertions(+), 4 deletions(-)