mirror of
https://github.com/openwrt/openwrt.git
synced 2024-12-21 14:37:57 +00:00
62 lines
2.0 KiB
Diff
62 lines
2.0 KiB
Diff
From patchwork Mon Aug 6 21:04:43 2012
|
|
Content-Type: text/plain; charset="utf-8"
|
|
MIME-Version: 1.0
|
|
Content-Transfer-Encoding: 7bit
|
|
Subject: [net-next] tcp: ecn: dont delay ACKS after CE
|
|
Date: Mon, 06 Aug 2012 11:04:43 -0000
|
|
From: Eric Dumazet <eric.dumazet@gmail.com>
|
|
X-Patchwork-Id: 175453
|
|
Message-Id: <1344287083.26674.83.camel@edumazet-glaptop>
|
|
To: David Miller <davem@davemloft.net>
|
|
Cc: netdev <netdev@vger.kernel.org>,
|
|
Neal Cardwell <ncardwell@google.com>
|
|
|
|
From: Eric Dumazet <edumazet@google.com>
|
|
|
|
While playing with CoDel and ECN marking, I discovered a
|
|
non optimal behavior of receiver of CE (Congestion Encountered)
|
|
segments.
|
|
|
|
In pathological cases, sender has reduced its cwnd to low values,
|
|
and receiver delays its ACK (by 40 ms).
|
|
|
|
While RFC 3168 6.1.3 (The TCP Receiver) doesn't explicitly recommend
|
|
to send immediate ACKS, we believe its better to not delay ACKS, because
|
|
a CE segment should give same signal than a dropped segment, and its
|
|
quite important to reduce RTT to give ECE/CWR signals as fast as
|
|
possible.
|
|
|
|
Note we already call tcp_enter_quickack_mode() from TCP_ECN_check_ce()
|
|
if we receive a retransmit, for the same reason.
|
|
|
|
Signed-off-by: Eric Dumazet <edumazet@google.com>
|
|
Cc: Neal Cardwell <ncardwell@google.com>
|
|
Acked-by: Neal Cardwell <ncardwell@google.com>
|
|
|
|
---
|
|
net/ipv4/tcp_input.c | 6 +++++-
|
|
1 file changed, 5 insertions(+), 1 deletion(-)
|
|
|
|
|
|
|
|
--
|
|
To unsubscribe from this list: send the line "unsubscribe netdev" in
|
|
the body of a message to majordomo@vger.kernel.org
|
|
More majordomo info at http://vger.kernel.org/majordomo-info.html
|
|
|
|
--- a/net/ipv4/tcp_input.c
|
|
+++ b/net/ipv4/tcp_input.c
|
|
@@ -231,7 +231,11 @@ static inline void TCP_ECN_check_ce(stru
|
|
tcp_enter_quickack_mode((struct sock *)tp);
|
|
break;
|
|
case INET_ECN_CE:
|
|
- tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
|
|
+ if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
|
|
+ /* Better not delay acks, sender can have a very low cwnd */
|
|
+ tcp_enter_quickack_mode((struct sock *)tp);
|
|
+ tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
|
|
+ }
|
|
/* fallinto */
|
|
default:
|
|
tp->ecn_flags |= TCP_ECN_SEEN;
|