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

[Eli Cohen]

On Tue, 2007-08-21 at 12:51 +0300, Or Gerlitz wrote:
> 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?
> 

You have the option to work in either connected or datagram mode, and
some might prefer to use datagram mode for various reasons. In these
cases you will want the benefits that LSO provides.