netdev - Re: [PATCH] net: Add ndo_gso

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Date:	Mon, 6 Oct 2014 23:22:29 +0300
From:	Or Gerlitz <gerlitz.or@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Alexander Duyck <alexander.h.duyck@...el.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Thomas Graf <tgraf@...g.ch>,
	Pravin Shelar <pshelar@...ira.com>,
	Andy Zhou <azhou@...ira.com>
Subject: Re: [PATCH] net: Add ndo_gso_check

On Mon, Oct 6, 2014 at 8:59 PM, Tom Herbert <therbert@...gle.com> wrote:
> On Sun, Oct 5, 2014 at 12:13 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>> RX wise, Linux tells the driver that UDP port X would be used for
>> VXLAN, right? and indeed, it's possible for some HW implementations
>> not to support RX offloading (checksum) for both VXLAN and NVGRE @ the
>> same time over the same port. But TX/GRO wise, you're probably
>> correct. The thing is that from the user POV they need solution that
>> works for both RX and TX offloading.

> I think from a user POV we want a solution that supports RX and TX
> offloading across the widest range of protocols. This is accomplished
> by implementing protocol agnostic mechanisms like CHECKSUM_COMPLETE
> and protocol agnostic UDP tunnel TSO like we've described. IMO, the
> fact that we have devices that implement protocol specific mechanisms
> for NVGRE and VXLAN should be considered legacy support in the stack,
> for new UDP encapsulation protocols we should not expose specifics in
> the stack in either by adding a GSO type for each protocol, nor
> ndo_add_foo_port for each protocol-- these things will not scale and
> unnecessarily complicate the core stack.

I tend to generally agree to the wind that blows from your writeup, namely:

UDP encapsulation offloads wise, we should pose few general
requirements to NICs to be implemented by vendors in their tomorrow's
HW and treat the current generation (these 4-5 drivers with their
limitations as legacy which should be supported but not state the
stack overall design).

Still we should seek more ways to reduce the pain/amount of
not-well-defined-configurations when these drivers are there and the
stack goes through this upside-down turnaround changes. OTOH you
didn't accept my SKB coloring suggestion for GSO inspection, and OTOH
I guess we can live with some sort of generic helper in the form of
what you suggested, but like it or not, getting rid of
ndo_add_vxlan_port will simply break things out.

Are we going to have a session on the encapsulation/offloads design @ LPC?

I think a replay of your LKS presentation along with open discussion
on how to get there with the legacy requirements could be very
helpful.

Or.
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