[ofa-general] checksum offload for IPonIB-CM

[Jason Gunthorpe]

On Fri, Apr 03, 2009 at 10:45:06AM -0700, Ted H. Kim wrote:

> Was there ever an idea that we could rely on
> the IB checksum to protect the
> payload instead? I vaguely remember some
> old presentation talking about checksum
> bypass or something similar.

Some patches were made but I don't think they were ever completed.

The difficulty was arranging things so that an absent checksum could
be negotiated and then ensuring that as the rx'd packet passed through
the Linux stack it was properly flagged as valid data, no checksum so
that the checksum is recomputed if the packet happens to be forwared
out another interface.

Essentially within the Linux architecture it would become similar to
how something like Xen works to provide checksum/segmentation offload
to VMs (and probably using the code they wrote..)

IIRC the interest was actually beyond just checksum but the whole bag
of tricks including segmentation offload. Essentially just connect two
Linux stacks together over RC with all the offload features turned on.

Jason