From a34a101e1e6365638b02ea83a38d7a4cb228dc04 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 18 May 2012 21:51:44 +0000 Subject: [PATCH] ipv6: disable GSO on sockets hitting dst_allfrag If the allfrag feature has been set on a host route (due to an ICMPv6 Packet Too Big received indicating a MTU of less than 1280), we hit a very slow behavior in TCP stack, because all big packets are dropped and only a retransmit timer is able to push one MSS frame every 200 ms. One way to handle this is to disable GSO on the socket the first time a super packet is dropped. Adding a specific dst_allfrag() in the fast path is probably overkill since the dst_allfrag() case almost never happen. Result on netperf TCP_STREAM, one flow : Before : 60 kbit/sec After : 1.6 Gbit/sec Reported-by: Tore Anderson Signed-off-by: Eric Dumazet Tested-by: Tore Anderson Signed-off-by: David S. Miller --- net/ipv6/ip6_output.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 3dc633f39372..d99fdc699625 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -643,7 +643,10 @@ int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *)) /* We must not fragment if the socket is set to force MTU discovery * or if the skb it not generated by a local socket. */ - if (!skb->local_df && skb->len > mtu) { + if (unlikely(!skb->local_df && skb->len > mtu)) { + if (skb->sk && dst_allfrag(skb_dst(skb))) + sk_nocaps_add(skb->sk, NETIF_F_GSO_MASK); + skb->dev = skb_dst(skb)->dev; icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu); IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), -- 2.20.1