diff options
| author | Eric Dumazet <eric.dumazet@gmail.com> | 2011-09-22 20:02:19 (GMT) |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2011-09-27 04:58:44 (GMT) |
| commit | 7a269ffad72f3604b8982fa09c387670e0d2ee14 (patch) | |
| tree | 3655a22066bcb1011e5e1b717a00a108143dfd85 | |
| parent | 0bdb0bd0139f3b6afa252de1487e3ce82a494db9 (diff) | |
| download | linux-7a269ffad72f3604b8982fa09c387670e0d2ee14.tar.xz | |
tcp: ECN blackhole should not force quickack mode
While playing with a new ADSL box at home, I discovered that ECN
blackhole can trigger suboptimal quickack mode on linux : We send one
ACK for each incoming data frame, without any delay and eventual
piggyback.
This is because TCP_ECN_check_ce() considers that if no ECT is seen on a
segment, this is because this segment was a retransmit.
Refine this heuristic and apply it only if we seen ECT in a previous
segment, to detect ECN blackhole at IP level.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Jamal Hadi Salim <jhs@mojatatu.com>
CC: Jerry Chu <hkchu@google.com>
CC: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
CC: Jim Gettys <jg@freedesktop.org>
CC: Dave Taht <dave.taht@gmail.com>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | include/net/tcp.h | 1 | ||||
| -rw-r--r-- | net/ipv4/tcp_input.c | 23 |
2 files changed, 17 insertions, 7 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h index f357bef..702aefc 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -356,6 +356,7 @@ static inline void tcp_dec_quickack_mode(struct sock *sk, #define TCP_ECN_OK 1 #define TCP_ECN_QUEUE_CWR 2 #define TCP_ECN_DEMAND_CWR 4 +#define TCP_ECN_SEEN 8 static __inline__ void TCP_ECN_create_request(struct request_sock *req, struct tcphdr *th) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index a5d01b1..5a4408c 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -217,16 +217,25 @@ static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp) tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; } -static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb) +static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb) { - if (tp->ecn_flags & TCP_ECN_OK) { - if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags)) - tp->ecn_flags |= TCP_ECN_DEMAND_CWR; + if (!(tp->ecn_flags & TCP_ECN_OK)) + return; + + switch (TCP_SKB_CB(skb)->flags & INET_ECN_MASK) { + case INET_ECN_NOT_ECT: /* Funny extension: if ECT is not set on a segment, - * it is surely retransmit. It is not in ECN RFC, - * but Linux follows this rule. */ - else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags))) + * and we already seen ECT on a previous segment, + * it is probably a retransmit. + */ + if (tp->ecn_flags & TCP_ECN_SEEN) tcp_enter_quickack_mode((struct sock *)tp); + break; + case INET_ECN_CE: + tp->ecn_flags |= TCP_ECN_DEMAND_CWR; + /* fallinto */ + default: + tp->ecn_flags |= TCP_ECN_SEEN; } } |