Re: [PATCH v3 0/3] enhance TX checksum command and csum forwarding engine

[Olivier MATZ <olivier.matz-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>]

Hi Jijiang,

On 01/21/2015 09:01 AM, Liu, Jijiang wrote:
>>> I still don't understand why you are so eager to 'forbid' it.
>>> Yes we support it for FVL, but no one forces you to use it.
>>
>> Well, how would you describe this 2 ways of doing the same thing in the
>> offload API? Would you talk about the i40e registers? It's not because i40e
>> has 2 ways to do the same operation that the DPDK should do the same.
>>
>> How will you explain to a user how to choose between these 2 cases?
>
> Talk about B method in http://dpdk.org/ml/archives/dev/2014-December/009213.html again.
>
> DPDK Never supports a  NIC that can recognize tunneling packet for TX side before 1.8, right?

When you say "recognize tunnel", if you mean offlading checksum of
tunnel headers, I agree.

If you mean recognizing a tunnel packet in rx, I also agree
it's new to dpdk-1.8, but I think it's unrelated to what we
are talking about, which is tx checksum. A DPDK application
is able to generate tunnel packets by itself and offload the
checksums to the NIC.

> So when we need to support TX checksum offload for tunneling packet,  and we have to choose B.2.

I don't see why we should choose either B.1 or B.2 (I guess you want
to say B.1 here, right?).

The m->lX_len are not filled in rx today. If one day they are, it won't
prevent the application to configure the lX_len fields and offload
flags according to the API.

> After introducing i40e(FVL),  FVL is able to recognize tunneling packet and  support outer IP, or inner IP or outer IP and inner IP TX checksum for tunneling packet.
> And you agree on "outer and inner at the same time", why do you object "only inner"?
>
> Actually, B.2 method is a software workaround using L2 length when NIC can't recognize tunneling packet.
> When NIC is able to recognize tunneling packet, I think you shouldn't take B.2 as a standard to 'forbid' other method.

Again, I'm not sure there is a link between "recognizing tunneling
packets" and tx checksum offload of tunnels.

Regards,
Olivier