[ofa-general] mlx4 second port lro issue

[Shirley Ma]

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