netdev - Re: [PATCH net-next 1/8] net: local checksum offload for encapsulation

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Date:	Thu, 28 Jan 2016 09:09:24 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Alexander Duyck <alexander.duyck@...il.com>
Cc:	Zang MingJie <zealot0630@...il.com>,
	Edward Cree <ecree@...arflare.com>,
	David Miller <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>, linux-net-drivers@...arflare.com
Subject: Re: [PATCH net-next 1/8] net: local checksum offload for encapsulation

On Thu, Jan 28, 2016 at 1:00 AM, Alexander Duyck
<alexander.duyck@...il.com> wrote:
> On Wed, Jan 27, 2016 at 11:04 PM, Zang MingJie <zealot0630@...il.com> wrote:
>> I have also noticed that for gso, all gso segs will have exactly same outer
>> udp checksum, this is also because inner checksum cancellation.
>>
>> Can we also optimize that outer udp checksum should be only calculated once
>> for all gso segs ?
>
> Actually that is a good point.  It isn't as if anything really changes
> in the tunnel headers between frames so we probably can just compute

This is probably true for current all implementation, but it has never
been declared as a requirement. It's conceivable that some
encapsulation layer might implement something like a sequence number
or its own CRC. The requirements should at least be documented.

Tom

> the outer once and then adjust it on the last frame to account for the
> fact that the length will be different.  I'll see if we can do that in
> the GSO patches I have been working on.
>
> - Alex