[ofa-general] [PATCH - 11] ipoib - add LSO support

[Or Gerlitz]

Eli Cohen wrote:
> On Mon, 2007-08-20 at 18:48 +0300, Or Gerlitz wrote:
> 
>> I see that the patch adds the NETIF_F_TSO flag to the device features 
>> but not the NETIF_F_UFO flag. Is UDP LSO supported by the connectX HW? 
>> if yes, what would it take SW wise to support it?
> 
> UDP LSO is not supported by the HW.

I see.


Reading http://en.wikipedia.org/wiki/TCP_segmentation_offload and 
thinking about the connectx TCP segmentation offloading a little further 
I am somehow confused:

With the ipoib connected mode a typical MTU exposed to the OS is 64K, 
where data goes over IB RC (soon to be UC) transport meaning that the 
HCA does the "fragmentation / reassembly" at the QP (IB L4) level 
allowing to send one 64K IB packet over a path whose Link layer (IB L2) 
MTU is 2k.

So TCP can use segments size upto 64K and UDP can send datagram's whose 
size is upto 64K without IP fragmentation.

With all this at hand, what does LSO buys you at all?

Or.