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

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Message-ID: <1476208321.448.5.camel@redhat.com>
Date:   Tue, 11 Oct 2016 19:52:01 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.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, 2016-10-11 at 11:42 -0600, Jason Gunthorpe wrote:
> 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.

AFAICS the max mtu is already underlying h/w dependent, how does such
differences are currently coped by ? (I'm sorry I lack some/a lot of IB
back-ground)