Re: [PATCH net-next] ipv6: disable GSO on sockets hitting dst_allfrag

From: Eric Dumazet <redacted>
Date: Sat, 19 May 2012 09:51:44 +0200

From: Eric Dumazet <edumazet@google.com>

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 <redacted>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Tore Anderson <redacted>

Applied.