netdev - RE: 2.6.20.7 mss negotiation and path mtu discovery mostly broken?

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Message-ID: <7CCD07160348804497EF29E9EA5560D7020F6213@exchtewks2.starentnetworks.com>
Date:	Wed, 25 Apr 2007 16:11:51 -0400
From:	"Ristuccia, Brian" <bristuccia@...rentnetworks.com>
To:	<netdev@...r.kernel.org>
Subject: RE: 2.6.20.7 mss negotiation and path mtu discovery mostly broken?

> I'm seeing a 
> problem where the kernel attempts to send packets with a MSS 
> larger than the one negotiated when the TCP connection is 
> established. Even after ICMP "can't fragment" messages 
> arrive, the kernel still attempts to increase the MSS rather 
> aggressively. The end result is extremely poor throughput 
> when sending to a network with a smaller MTU. 

I've tracked this problem to the TSO feature in the bnx2 driver. Turning
off TSO with "ethtool -K eth1 tso off" seems to work around the problem.
It appears that the bnx2 device is not using the correct mss when
performing segmentation offload. 

-Brian

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