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Date: Mon, 31 Aug 2009 16:23:31 +0300 (EEST)
From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To: Damian Lukowski <damian@....rwth-aachen.de>
cc: Netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 2/3] Revert Backoff [v3]: Revert RTO on ICMP destination
unreachable
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@....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@...sinki.fi>
--
i.
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