Commit 7a269ffa authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

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: default avatarEric 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: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0bdb0bd0
......@@ -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)
......
......@@ -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;
}
}
......
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