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

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Message-ID: <CA+mtBx-t2a80VhYypH8d0pjWh7FqT8GRGZt1F=o23GC3BZm-sA@mail.gmail.com>
Date:	Mon, 3 Nov 2014 14:39:31 -0800
From:	Tom Herbert <therbert@...gle.com>
To:	Jesse Gross <jesse@...ira.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 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?

Thanks,
Tom
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