From: Eric Dumazet <edumazet@google.com>
Date: Fri, 18 May 2012 21:51:44 +0000 (+0000)
Subject: ipv6: disable GSO on sockets hitting dst_allfrag
X-Git-Tag: v3.5-rc1~191^2~15
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a34a101e1e6365638b02ea83a38d7a4cb228dc04;p=pandora-kernel.git

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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