On Thu, Apr 28, 2016 at 6:18 PM, Matthew Finlay [off-list ref] wrote:

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The mlx5 hardware requires the outer UDP checksum is not set when offloading encapsulated packets.

The Intel documentation said the same thing.  That was due to the fact
that the hardware didn't computer the outer UDP header checksum.  I
suspect the Mellanox hardware has the same issue.  Also I have tested
on a ConnectX-4 board with the latest firmware and what I am seeing is
that with my patches applied the outer checksum is being correctly
applied for segmentation offloads.

My thought is that that the hardware appears to ignore the UDP
checksum so if it is non-zero you cannot guarantee the checksum would
be correct on the last frame if it is a different size than the rest
of the segments.  In the case of these patches that issue has been
resolved as I have precomputed the UDP checksum for the outer UDP
header and all of the segments will be the same length so there should
be no variation in the UDP checksum of the outer header.  Unless you
can tell my exactly the reason why we cannot provide the outer UDP
checksum I would assume that the reason is due to the fact that the
hardware doesn't compute it so you cannot handle a fragment on the end
which is resolved already via GSO_PARTIAL.

I will check internally and verify there are no unforeseen issues with setting the outer UDP checksum in this scenario.

Thanks.  Any idea how long it should be.  I know I was getting a
auto-reply about people being out until May 1st due to a holiday so I
am just wondering if we should have Dave drop this patch set and I
submit a v2 when you can get me the feedback next week, or if we run
with the patches as-is for now and be prepared to revert if anything
should come up.

- Alex