Re: [PATCH] IB/ipoib: move back the IB LL address into the hard header

On 10/11/2016 1:32 PM, Jason Gunthorpe wrote:

On Tue, Oct 11, 2016 at 07:15:44PM +0200, Paolo Abeni wrote:

quoted

Also the connected mode maximum mtu is reduced by 16 bytes to
cope with the increased hard header len.

Changing the MTU is going to cause annoying interop problems, can you
avoid this?

(Paolo did the work I'm describing here, I'm just giving the explanation
he gave me):

Not using this particular solution I don't think.  We tried it without
increasing the declared hard header length and it broke when dealing
with skb_clone/GSO paths.  In order to make the LL pseudo header get
copied along with the rest of the encap and data on clone, we had to
declare the header.  The problem then became that the sg setup is such
that we are limited to 16 4k pages for the sg array, so that header had
to come out of the 64k maximum mtu.

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Doug Ledford [off-list ref]
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