Date:	Mon, 6 Oct 2014 17:17:56 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Jesse Gross <jesse@...ira.com>
Cc:	Or Gerlitz <gerlitz.or@...il.com>,
	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 3:33 PM, Jesse Gross <jesse@...ira.com> wrote:
> On Mon, Oct 6, 2014 at 10:59 AM, Tom Herbert <therbert@...gle.com> wrote:
>> On Sun, Oct 5, 2014 at 12:13 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>>> On Sun, Oct 5, 2014 at 9:49 PM, Tom Herbert <therbert@...gle.com> wrote:
>>>> On Sun, Oct 5, 2014 at 7:04 AM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>>>>> On Thu, Oct 2, 2014 at 2:06 AM, Tom Herbert <therbert@...gle.com> wrote:
>>>>>> On Wed, Oct 1, 2014 at 1:58 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
>>>>>>> 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:
>>>>> [...]
>>>>>> Solution #4: apply this patch and implement the check functions as
>>>>>> needed in those 4 or 5 drivers. If a device can only do VXLAN/NVGRE
>>>>>> then I believe the check function is something like:
>>>>>>
>>>>>> bool mydev_gso_check(struct sk_buff *skb, struct net_device *dev)
>>>>>> {
>>>>>>         if ((skb_shinfo(skb)->gso_type & SKB_GSO_UDP_TUNNEL) &&
>>>>>>             ((skb->inner_protocol_type != ENCAP_TYPE_ETHER ||
>>>>>>               skb->protocol != htons(ETH_P_TEB) ||
>>>>>>               skb_inner_mac_header(skb) - skb_transport_header(skb) != 12)
>>>>>>                 return false;
>>>>>>
>>>>>>         return true;
>>>>>> }
>>>>>
>>>>> Yep, such helper can can be basically made to work and let the 4-5
>>>>> drivers that can
>>>>> do GSO offloading for vxlan but not for any FOU/GUE packets signal
>>>>> that to the stack.
>>>>>
>>>>> Re the 12 constant, you were referring to the udp+vxlan headers? it's 8+8
>>>>>
>>>>> Also, we need a way for drivers that can support VXLAN or NVGRE but
>>>>> not concurrently
>>>>> on the same port @ the same time to only let vxlan packet to pass
>>>>> successfully through the helper.
>>>
>>>> Or, there should be no difference in GSO processing between VXLAN and
>>>> NVGRE. Can you explain why you feel you need to differentiate them for GSO?
>>>
>>>
>>> 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.
>
> It's not clear to me that allowing devices to know what protocols are
> running on what ports actually complicates the stack. The part that is
> complicated is usually the types of operations that are being
> offloaded (checksum, TSO, etc.). In all of these tunnel cases, the
> operations are same and if you have a clean registration mechanism
> then nothing in the core has to see this - only the protocol doing the
> registering and the driver that is supporting it.
>

We already have an ntuple filtering interface that allows configuring
a device for special processing of RX packets. I don't see why that
shouldn't apply to the use case protocol processing for specific ports
in the encapsulation use case.

> I have no disagreement with trying to be generic across protocols. I'm
> just not convinced that it is a realistic plan. It's obvious that it
> is not doable today nor will be it be in the next generation of NICs
> (which are guaranteed to add support for new protocols). Furthermore,
> there will be more advanced stuff coming in the future that I think
> will be difficult or impossible to make protocol agnostic. Rather than
> pretending that this doesn't exist or will never happen, it's better
> focus on how to integrating it cleanly.

Sorry, but I don't understand how supporting a new protocols in a
device for the purposes of returning CHECKSUM_UNNECESSARY is better or
easier to implement than just returning CHECKSUM_COMPLETE. Same thing
for trying to use NETIF_F_IP_CSUM with encapsulation rather than
NETIF_F_HW_CSUM. I'm not a hardware guy, so it's possible I'm missing
something obvious...

Can you be more specific about this "advanced stuff"?

Thanks,
Tom
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