From 7a269ffad72f3604b8982fa09c387670e0d2ee14 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 22 Sep 2011 20:02:19 +0000
Subject: [PATCH] tcp: ECN blackhole should not force quickack mode
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit
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>
---
include/net/tcp.h | 1 +
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 f357befaaa018..702aefc8d43da 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 a5d01b183cf71..5a4408c55155c 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;
}
}
--
2.30.2