[ofa-general] mlx4 second port lro issue

[Boris Shpolyansky]

Shirley,

Are you referring to actual Ethernet frame size or to TCP message size?
If the port MTU set to 1500 it will reject Ethernet frames larger than
this size, this has nothing to do with the LRO. 
LRO is a TCP offload that improves CPU utilization on the TCP receiver
by combining multiple packets belonging to the same TCP stream to a
single buffer and transferring it to the TCP stack as a single large
packet.

Boris Shpolyansky
Sr. Member of Technical Staff, Applications
 
Mellanox Technologies Inc.
350 Oakmead Parkway, Suite 100
Sunnyvale, CA 94085
Tel.: (408) 916 0014
Fax: (408) 585 0314
Cell: (408) 834 9365
www.mellanox.com

-----Original Message-----
From: Shirley Ma [mailto:mashirle at us.ibm.com] 
Sent: Thursday, September 10, 2009 7:08 PM
To: Boris Shpolyansky
Cc: Roland Dreier; general at lists.openfabrics.org
Subject: RE: [ofa-general] mlx4 second port lro issue

Hello Boris,

On Thu, 2009-09-10 at 14:16 -0700, Boris Shpolyansky wrote:
> Dumb question: what was the MTU setting of the eth interface
> associated
> with port 2? Dropping jumbo frames has nothing to do with LRO - it is
> plain layer 2 functionality.

ifconfig shows both port1 and port2 mtu are 1500. port 2 does't drop
jumbo frames. The problem is the LRO is on for both interfaces so the
interface will get large packet (packet size 1848). port1 can receive it
and process it, but not port2. If I disables lro by reloading module
with num_lro=0, then it will get small packet, and port2 works fine. 

My question here is why port1 can work well for lro but not port2.

Thanks
Shirley