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

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Date:   Tue, 11 Oct 2016 11:42:24 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     linux-rdma@...r.kernel.org, Doug Ledford <dledford@...hat.com>,
        Sean Hefty <sean.hefty@...el.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH] IB/ipoib: move back the IB LL address into the hard
 header

On Tue, Oct 11, 2016 at 07:37:32PM +0200, Paolo Abeni wrote:
> On Tue, 2016-10-11 at 11:32 -0600, Jason Gunthorpe wrote:
> > On Tue, Oct 11, 2016 at 07:15:44PM +0200, Paolo Abeni wrote:
> > 
> > > 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?
> 
> I don't like changing the maximum MTU value, too, but I was unable to
> find an alternative solution. The PMTU detection should protect against
> such issues.

It is more that PMTU, we have instructed all users that is the MTU
number needed to enable CM mode, so it appears in documentation,
scripts, etc.

There is really no way to re-use some of the existing alignment
padding or exceed 64k?

Jason