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tcp: ECN blackhole should not force quickack mode

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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>
This commit is contained in:
Eric Dumazet 2011-09-22 20:02:19 +00:00 committed by David S. Miller
parent 0bdb0bd013
commit 7a269ffad7
2 changed files with 17 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/tcp.h
View File

@ -356,6 +356,7 @@ static inline void tcp_dec_quickack_mode(struct sock *sk,
#define TCP_ECN_OK 1 #define TCP_ECN_OK 1
#define TCP_ECN_QUEUE_CWR 2 #define TCP_ECN_QUEUE_CWR 2
#define TCP_ECN_DEMAND_CWR 4 #define TCP_ECN_DEMAND_CWR 4
#define TCP_ECN_SEEN 8
static __inline__ void static __inline__ void
TCP_ECN_create_request(struct request_sock *req, struct tcphdr *th) TCP_ECN_create_request(struct request_sock *req, struct tcphdr *th)

23
net/ipv4/tcp_input.c
View File

@ -217,16 +217,25 @@ static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR; 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 (!(tp->ecn_flags & TCP_ECN_OK))
if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags)) return;
tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
switch (TCP_SKB_CB(skb)->flags & INET_ECN_MASK) {
case INET_ECN_NOT_ECT:
/* Funny extension: if ECT is not set on a segment, /* Funny extension: if ECT is not set on a segment,
* it is surely retransmit. It is not in ECN RFC, * and we already seen ECT on a previous segment,
* but Linux follows this rule. */ * it is probably a retransmit.
else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags))) */
if (tp->ecn_flags & TCP_ECN_SEEN)
tcp_enter_quickack_mode((struct sock *)tp); 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;
} }
} }