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: NTore Anderson <tore@fud.no> Signed-off-by: NEric Dumazet <edumazet@google.com> Tested-by: NTore Anderson <tore@fud.no> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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