[xdp-hints] Re: XDP-hints presentation at LLC2022

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 14/06/2022 12.40, Bezdeka, Florian wrote:
> 
> On Mon, 2022-05-16 at 16:41 +0200, Alexander Lobakin wrote:
>> From: Jesper Dangaard Brouer <jbrouer@redhat.com>
>> Date: Mon, 16 May 2022 15:58:06 +0200
>>
>>> Hi XDP-hints community,
>>
>> Hey!

Happy to see you Florian joining the XDP-hints community mailing-list.

>>>
>>> Gave this talk[1] on Friday (13 May) "XDP hints via BPF" at Lund Linux
>>> Con.  In the talk we are proposing several *possible* solutions, with
>>> "pros" and "cons".  We are open to new ideas, proposals and critique.
>>>
>>> I will play with implementing some of these ideas and to see if they
>>> pan-out.  I want to acknowledge that Alexander Lobakin (+ co-authors)
>>> also have started coding on solutions here[3].  Lets see if we can
>>> collaborate and find a solution we can all agree on.
>>
>> Nice catch about "it makes it possible to make NIC driver L2
>> only" -- it's not present in the current code, but we're thinking
>> of this for some time already :)
>> Re collaborate -- I'm expecting the first RFC to hit internal review
>> in 2-3 weeks, hope it will get posted to LKML soon after that. GH
>> tree should be finalized this week, so you could start playing.
> 
> Is there something already available that would allow us to start
> playing with xdp hints?

I have some working kernel-side code (that Lorenzo is doing internal
review of), but I've been sick so I've not had time to cleanup and send
on the (bpf-kernel) list. I'll try to get an RFC out tomorrow.

Is your use-case AF_XDP related?

For AF_XDP we/you also need to decode the BTF-format in userspace, to
interpret what layout the kernel or XDP BPF-prog are providing in the
metadata area XDP-hints.

We have a simple BTF-format decoder in this bpf-example[0] what was
developed in collaboration with a large Wind-Turbine producers use-case.
  The example doesn't rely on any kernel changes, as we only depend on
the XDP BPF-prog to provide BTF-info and software RX-timestamps. Thus,
this is a "software only" solution, and we need my mentioned kernel
changes to get access to the hardware (XDP) hints. This is something you
can "start playing with" right now.

  [0] 
https://github.com/xdp-project/bpf-examples/tree/master/AF_XDP-interaction


> The main focus for us would be forwarding meta information like TX/RX
> hardware timestamps from/into the AF_XDP application. The slides
> mention that already, so it seems to be "in scope".
> 
> In addition I would like to learn which drivers you are primarily
> targeting. Especially if drivers for Intel i210 (igb) and i225 (igc)
> cards are on your radar.

Yes, Intel i210 (driver igb) and i225 (driver igc) are very much on my
radar and in my testlab.  The mentioned embedded project were
investigating these as part of the hardware evaluation.

We need to land RX-side of XDP-hints *first*, but the longer term plan
is to support TX-side hints.  Specifically I've looked into hardware
LaunchTime features supported by chips i210 and i225.  I've documented
the low-level register differences here[4], which shows we need some
translation layer as driver level (as e.g. bits and granularity differ
between chips for same "perceived" feature).

  [4] 
https://github.com/xdp-project/xdp-project/blob/master/areas/tsn/code01_follow_qdisc_TSN_offload.org


>>>
>>> [1] Slide PDF:
>>> https://github.com/xdp-project/xdp-project/blob/master/conference/LLC2022/xdp_hints_hw_metadata-final.pdf
>>>
>>> [2] Slide source:
>>> https://github.com/xdp-project/xdp-project/tree/master/conference/LLC2022
>>>
>>> [3] https://github.com/alobakin/linux/commits/xdp_hints

--Jesper