[ofa-general] [PATCHv2] IB/ipoib: S/G and HW checksum support

[Or Gerlitz]

Jason Gunthorpe wrote:
> On Wed, Sep 05, 2007 at 11:35:06PM +0300, Or Gerlitz wrote:

>> I guess by "RC" you mean connected mode. The connected mode is now
>> implemented over RC but as was discussed over this list few times, it
>> should (and it would) move to use UC, which is also much easier to
>> implement in hw based gateways. Anyway, your idea to allow this
>> feature coming into play only under negotiation schem sounds fine to
>> me, however:

> Sure.. Though, I'm not sure what advantage UC/RC brings to a gateway app
> when you can't pass 64k MTU onto ethernet...

When the Ethernet side supports 9K Jumbo frames, if connected mode comes 
into play then there should be a performance increase, so the gateway 
negotiates the MTU to be 9K and so on.

> Right, but I'm not suggesting using the chips offload.

> Micheal has made it so you can use 'csum offload' (via disabling csum)
> on any nic. You can also do the same kind of thing for TSO/GSO. If you
> send jumbo TSO/GSO packets in a chunk the receiver can then do
> LRO. Win all around. Sort of like jumbo MTU but without actually
> changing the MTU.
> 
> This is all basically the same set of techniques we see between a
> Linux guest and the linux host in a virtualization environment.

Thanks for the clarification, I have to do some catchup here on the 
details re TSO/GSO and their relation to virtualization, however, to 
make things a little clearer to me, do you agree that as James pointed 
over this thread in

A (IB) ---- B (Gateway eg HW based) ---- C (Ethernet)

scheme, in case A does not compute the TCP checksum of a packet,  its 
note the role of the gateway to do so, and C would just drop it?!

Or.