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

[Michael S. Tsirkin]

> Quoting Or Gerlitz <ogerlitz at voltaire.com>:
> Subject: Re: [PATCH - 11] ipoib - add LSO support
> 
> 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?

If you read these patches closely, you'll see that LSO
is disabled for connected mode.

-- 
MST