netdev - Re: [PATCH net-next 3/3] vxlan: Remote checksum offload

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Date:	Tue, 25 Nov 2014 10:54:26 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/3] vxlan: Remote checksum offload

On Mon, Nov 24, 2014 at 6:50 PM, Tom Herbert <therbert@...gle.com> wrote:
> On Mon, Nov 24, 2014 at 5:06 PM, Jesse Gross <jesse@...ira.com> wrote:
>> On Mon, Nov 24, 2014 at 3:52 PM, Tom Herbert <therbert@...gle.com> wrote:
>>> Add support for remote checksum offload in VXLAN. This commandeers a
>>> reserved bit to indicate that RCO is being done, and uses the low order
>>> reserved eight bits of the VNI to hold the start and offset values in a
>>> compressed manner.
>>
>> Why do you think that this is OK for you to do? It's clear that there
>> is no consensus for this (and in fact there are other proposals that
>> use that bit in a different way).
>
> I asked on nvo3 list (which I believe is the appropriate forum) what
> the best way to do this is but haven't gotten any response. I will ask
> again-- I would assume that with an implementation and data in hand
> that might be better basis for discussion.
>
> The flag bit is currently unused in the Linux implementation, so I
> don't think it can break anything as of now. I suppose we could make
> RCO for VXLAN a config option and possibly change to use a different
> if consensus is reached on the right approach in the future.

This will definitely break things if this is applied now and the bit
is later used for a different purpose in the future as there will be
no way to update existing deployments.

There are a ton of conflicting proposals in this space so I think
there are only two possible solutions at this point:
 * Potentially support all of them and chose a variant at runtime
though a series of configuration options. This seems ugly,
particularly for GRO.
 * Stick to the version described in the RFC.

I don't think the third alternative of protocol design by order of
patch submission is viable.
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