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 <tore@fud.no> Signed-off-by: Eric Dumazet <edumazet@google.com> Tested-by: Tore Anderson <tore@fud.no> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -643,7 +643,10 @@ int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
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/* We must not fragment if the socket is set to force MTU discovery
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* or if the skb it not generated by a local socket.
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*/
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if (!skb->local_df && skb->len > mtu) {
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if (unlikely(!skb->local_df && skb->len > mtu)) {
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if (skb->sk && dst_allfrag(skb_dst(skb)))
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sk_nocaps_add(skb->sk, NETIF_F_GSO_MASK);
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skb->dev = skb_dst(skb)->dev;
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icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
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IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
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