netdev - Re: [PATCH net-next 0/7] gue: Remote checksum offload

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Message-ID: <CAEP_g=-rgL1D3kEQaCCmgArsVZQ0D=-JxDjoyZut3iykASYjNQ@mail.gmail.com>
Date:	Mon, 3 Nov 2014 16:19:39 -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 0/7] gue: Remote checksum offload

On Mon, Nov 3, 2014 at 2:39 PM, Tom Herbert <therbert@...gle.com> wrote:
> On Mon, Nov 3, 2014 at 1:26 PM, Jesse Gross <jesse@...ira.com> wrote:
>> On Sat, Nov 1, 2014 at 3:57 PM, Tom Herbert <therbert@...gle.com> wrote:
>>> This patch set implements remote checksum offload for
>>> GUE, which is a mechanism that provides checksum offload of
>>> encapsulated packets using rudimentary offload capabilities found in
>>> most Network Interface Card (NIC) devices. The outer header checksum
>>> for UDP is enabled in packets and, with some additional meta
>>> information in the GUE header, a receiver is able to deduce the
>>> checksum to be set for an inner encapsulated packet. Effectively this
>>> offloads the computation of the inner checksum. Enabling the outer
>>> checksum in encapsulation has the additional advantage that it covers
>>> more of the packet than the inner checksum including the encapsulation
>>> headers.
>>
>> Tom, I have a pretty hard time squaring this with your previous
>> comments on hardware offload. This looks almost identical to a
>> protocol-specific hardware offload to me in terms of the implications
>> on the stack. It actually is more invasive and less likely to scale
>> across protocols, so the relative cost/benefit doesn't really add up
>> in my mind.
>
> With this patch and checksum-unnecessary conversion we can provide
> checksum offload for encapsulation on millions of already deployed
> NICs without any HW or FW change.  Why do you think this is not a good
> cost/benefit tradeoff?

I just don't see how this is consistent with your previously stated
goal of keeping protocol-specific offload code out of the core stack.
Can you explain how this is different?
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