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

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Date:   Wed, 12 Oct 2016 14:21:46 -0400
From:   Doug Ledford <dledford@...hat.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     Paolo Abeni <pabeni@...hat.com>, linux-rdma@...r.kernel.org,
        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 10/11/2016 2:50 PM, Doug Ledford wrote:
> On 10/11/2016 2:30 PM, Jason Gunthorpe wrote:
>> On Tue, Oct 11, 2016 at 02:17:51PM -0400, Doug Ledford wrote:
>>
>>> Well, not exactly.  Even if we put 65520 into the scripts, the kernel
>>> will silently drop it down to 65504.  It actually won't require anyone
>>> change anything, they just won't get the full value.  I experimented
>>> with this in the past for other reasons and an overly large MTU setting
>>> just resulted in the max MTU.  I don't know if that's changed, but if it
>>> still works that way, this is much less of an issue than it might
>>> otherwise be.
>>
>> So it is just docs and relying on PMTU? That is not as bad..
>>
>> Still would be nice to avoid if at all possible..
> 
> I agree, but we have a test getting ready to commence.  We'll know
> shortly how much the reduced MTU effects things because they aren't
> going to alter any of their setup, just put the new kernel in place, and
> see what happens.
> 
> 

Long story short on the MTU stuff, the setups whined a bit about not
being able to set the desired MTU, used the new max MTU instead, and
things otherwise worked fine.  But, Paolo submitted a v2 patch that
removes this change, so it's all moot anyway.

-- 
Doug Ledford <dledford@...hat.com>
    GPG Key ID: 0E572FDD



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