[ofa-general] mlx4 second port lro issue

[Barry Mavin]

Is this a subnet manager issue?

Configure your Subnet Manager (SM) to set the MTU value in
the configuration file. The SM configuration for MTU value is per Partition
Key (PKey). For example, to enable 4052-byte MTUs on a default PKey using
the OpenSM SM, log into the Linux machine (running OpenSM) and perform the
following commands:
1. Edit the file:
   /usr/local/ofed/etc/opensm/partitions.conf
   and include the line:
   key0=0x7fff,ipoib,mtu=5 : ALL=full;

---
Regards
Barry Mavin
Recital Corporation
Chairman and CEO
Website: http://www.recital.com
MSN Messenger: Barry_Mavin at msn.com
Skype: BarryMavin
Direct line worldwide: +1 9785224139



> From: Shirley Ma <mashirle at us.ibm.com>
> Date: Thu, 10 Sep 2009 20:02:47 -0700
> To: Boris Shpolyansky <boris at mellanox.com>
> Cc: Roland Dreier <rdreier at cisco.com>, <general at lists.openfabrics.org>
> Subject: RE: [ofa-general] mlx4 second port lro issue
> 
> Hello Boris,
> 
> On Thu, 2009-09-10 at 19:31 -0700, Boris Shpolyansky wrote:
>> 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.
> 
> Because the LRO is enabled in device driver level, when it receives
> multiple tcp fragmentation packets, it will merge to a large packet to
> deliver to upper layer protocol to process. However, the port1 works
> well, but not for port2 when LRO enabled.
> 
> I don't know when the packet drops since I don't have any tool rather
> than tcpdump. From tcpdump I can see the large packet when I use port1,
> but I can't see the large packet when I use port2 with LRO enabled. If I
> disabled LRO, all packets are smaller than 1500 mtu from tcpdump,
> everything works fine for both ports. I hope it's clear.
> 
> Thanks
> Shirley
> 
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