netdev - Re: [PATCH] net: Add ndo_gso

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Message-ID: <CAJ3xEMhc-97+3ZDwqXzX2N+=voO4QvJ5_YXn3sp8r8E9YyqotQ@mail.gmail.com>
Date:	Wed, 1 Oct 2014 23:58:02 +0300
From:	Or Gerlitz <gerlitz.or@...il.com>
To:	Tom Herbert <therbert@...gle.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	John Fastabend <john.r.fastabend@...el.com>
Cc:	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 Tue, Sep 30, 2014 at 6:34 PM, Tom Herbert <therbert@...gle.com> wrote:
> On Tue, Sep 30, 2014 at 7:30 AM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>> On Tue, Sep 30, 2014 at 12:38 AM, Tom Herbert <therbert@...gle.com> wrote:
>>> On Mon, Sep 29, 2014 at 2:10 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>>>> On Mon, Sep 29, 2014 at 11:53 PM, Tom Herbert <therbert@...gle.com> wrote:
>>>>> On Mon, Sep 29, 2014 at 12:59 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>>>>>> On Mon, Sep 29, 2014 at 6:50 AM, Tom Herbert <therbert@...gle.com> wrote:

>> I'm not sure how exactly this (inner protocol being Ethernet and inner
>> header lengths)
>> is going to work to differentiate between VXLAN and NVGRE (or @ least
>> the GRE-ing done by OVS on guest Ethernet frames).

> GSO processing for VXLAN and NVGRE should be identical. They both have
> a four byte header that needs to be copied per packet and both only
> carry Ethernet frames.

I know and indeed in the mlx4 case, the HW (ConnectX3-pro NIC) that
supports VXLAN offloads also supports NVGRE, but generally speaking, I
can't commit for other vendors HW/driver which support VXLAN today.


> This would be equivalent to adding more protocol specific GSO feature
> bits. I still don't see how this will scale. The number of protocols
> that we might want to encapsulate over UDP is vast-- even before FOU
> adding possibility of encapsulating any IP protocol in UDP. And, as
> already pointed out, devices might have other arbitrary limitations
> such as length of inner headers that wouldn't easily be represented in features.


> Also, this does not benefit the stack or drivers that already support
> generic SKB_GSO_UDP_TUNNEL mechanism.

But again, we have 4-5 drivers that are

1. upstream
2. support GSO offloading under VXLAN
3. advertize GSO_UDP_TUNNEL

As a starting point to stabilize the system (3.18 which has FOU and
friends, merge window coming up while we are @ LPC) we can

1. add GSO_UDP_VXLAN_TUNNEL type

2. ask each maintainer to decide if they want to advertize the generic tunnel
or only the vxlan specific one

3. color udp tunneled skb's with the tunnel type being vxlan or something else

have today's code that decides if to do SW GSO or HW GSO choose according
to the skb color and the driver posted value.

> Would any other driver maintainers like to chime in on this?

Alex? John?
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