diff options
| -rw-r--r-- | target/linux/generic/patches-3.3/060-tcp-ecn-dont-delay-ACKS-after-CE.patch | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/target/linux/generic/patches-3.3/060-tcp-ecn-dont-delay-ACKS-after-CE.patch b/target/linux/generic/patches-3.3/060-tcp-ecn-dont-delay-ACKS-after-CE.patch new file mode 100644 index 0000000000..547e4faf73 --- /dev/null +++ b/target/linux/generic/patches-3.3/060-tcp-ecn-dont-delay-ACKS-after-CE.patch @@ -0,0 +1,63 @@ +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 + +diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c +index 2fd2bc9..fa2c2c2 100644 +--- a/net/ipv4/tcp_input.c ++++ b/net/ipv4/tcp_input.c +@@ -237,7 +237,11 @@ static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *s + 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; |