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

[Michael S. Tsirkin]

> Quoting Jason Gunthorpe <jgunthorpe at obsidianresearch.com>:
> Subject: Re: [ofa-general] [PATCHv2] IB/ipoib: S/G and HW checksum support
> 
> On Thu, Sep 06, 2007 at 09:40:11AM +0300, Or Gerlitz wrote:
> 
> > >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?!
> 
> I think the proper way to view Michael's patch, and indeed this whole
> idea, is that it just moves the work around, with the goal of
> eliminating the work for a class of communication (Linux host to Linux
> host). So yes, if a gateway uses this feature then it must regenerate
> the checksum before it forwards it.
> 
> It is actually a pretty neat idea, I've never heard of another network
> doing this. I wouldn't call it hardware checksum, but more like a
> peer-to-peer VNIC scheme. Nobody would object if a vnic driver moved
> checksum and segmentation offload to the VNIC device over a RC QP, and
> I think the same rational for that applies here, except it is now peer
> to peer. (Michael maybe that is a good name for this concept: p2p_vnic?)

Yea. Roland, does the argument sound convincing to you?

> FWIW, general gateways do have a bit of a problem doing the csum
> insertion because there are alot of cases and new protocols do crop up
> from time to time. It would be best if part of the information sent in
> this case was instructions on how to do the insertion like an general
> ethernet chip would use.

Not sure I know what do you mean. Could you give an example please?

-- 
MST