netdev - Re: [PATCH v1 1/6] net: Generalize udp based tunnel offload

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Date:	Tue, 1 Dec 2015 16:40:22 -0800
From:	"Singhai, Anjali" <anjali.singhai@...el.com>
To:	"John W. Linville" <linville@...driver.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Tom Herbert <tom@...bertland.com>, Jesse Gross <jesse@...nel.org>,
	David Miller <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Kiran Patil <kiran.patil@...el.com>
Subject: Re: [PATCH v1 1/6] net: Generalize udp based tunnel offload



On 12/1/2015 8:08 AM, John W. Linville wrote:
> On Tue, Dec 01, 2015 at 04:49:28PM +0100, Hannes Frederic Sowa wrote:
>> On Tue, Dec 1, 2015, at 16:44, John W. Linville wrote:
>>> On Mon, Nov 30, 2015 at 09:26:51PM -0800, Tom Herbert wrote:
>>>> On Mon, Nov 30, 2015 at 5:28 PM, Jesse Gross <jesse@...nel.org> wrote:
>>>>> Based on what we can do today, I see only two real choices: do some
>>>>> refactoring to clean up the stack a bit or remove the existing VXLAN
>>>>> offloading altogether. I think this series is trying to do the former
>>>>> and the result is that the stack is cleaner after than before. That
>>>>> seems like a good thing.
>>>> There is a third choice which is to do nothing. Creating an
>>>> infrastructure that claims to "Generalize udp based tunnel offload"
>>>> but actually doesn't generalize the mechanism is nothing more than
>>>> window dressing-- this does nothing to help with the VXLAN to
>>>> VXLAN-GPE transition for instance. If geneve specific offload is
>>>> really needed now then that can be should with another ndo function,
>>>> or alternatively ntuple filter with a device specific action would at
>>>> least get the stack out of needing to be concerned with that.
>>>> Regardless, we will work optimize the rest of the stack for devices
>>>> that implement protocol agnostic mechanisms.
>>> Is there no concern about NDO proliferation? Does the size of the
>>> netdev_ops structure matter? Beyond that, I can see how a single
>>> entry point with an enum specifying the offload type isn't really any
>>> different in the grand scheme of things than having multiple NDOs,
>>> one per offload.
>>>
>>> Given the need to live with existing hardware offloads, I would lean
>>> toward a consolidated NDO. But if a different NDO per tunnel type is
>>> preferred, I can be satisified with that.
>> Having per-offloading NDOs helps the stack to gather further information
>> what kind of offloads the driver has even maybe without trying to call
>> down into the layer (just by comparing to NULL). Checking this inside
>> the driver offload function clearly does not have this feature. So we
>> finally can have "ip tunnel please-recommend-type" feature. :)
> That is a valuable insight! Maybe the per-offload NDO isn't such a
> bad idea afterall... :-)
>
> John
This helps me understand why having a separate ndo op might still be ok. 
Thanks for the feedback. I will go back to that model.  Also  I think I 
did finally understand the discussion on using a single 2's compliment 
checksum method
for future silicon.
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