[xdp-hints] Re: [PATCH bpf-next v2 0/3] xsk: TX metadata txtime support

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 12/1/23 16:09, Willem de Bruijn wrote:
> Song, Yoong Siang wrote:
>> On Friday, December 1, 2023 6:46 PM, Jesper Dangaard Brouer <hawk@kernel.org> wrote:
>>> On 12/1/23 07:24, Song Yoong Siang wrote:
>>>> This series expands XDP TX metadata framework to include ETF HW offload.
>>>>
>>>> Changes since v1:
>>>> - rename Time-Based Scheduling (TBS) to Earliest TxTime First (ETF)
>>>> - rename launch-time to txtime
>>>>
>>>
>>> I strongly disagree with this renaming (sorry to disagree with Willem).
>>>
>>> The i210 and i225 chips call this LaunchTime in their programmers
>>> datasheets, and even in the driver code[1].
>>>
>>> Using this "txtime" name in the code is also confusing, because how can
>>> people reading the code know the difference between:
>>>   - tmo_request_timestamp and tmo_request_txtime
>>>
>>
>> Hi Jesper and Willem,
>>
>> How about using "launch_time" for the flag/variable and
>> "Earliest TxTime First" for the description/comments?
> 

I don't follow why you are calling the feature:
  - "Earliest TxTime First" (ETF).
  - AFAIK this just reference an qdisc name (that most don't know exists)


> I don't particularly care which term we use, as long as we're
> consistent. Especially, don't keep introducing new synonyms.
> 
> The fact that one happens to be one vendor's marketing term does not
> make it preferable, IMHO. On the contrary.
>

These kind of hardware features are defined as part of Time Sensitive
Networking (TSN).
I believe these TSN features are defined as part of IEEE 802.1Qbv (2015)
and according to Wikipedia[2] incorporated into IEEE 802.1Q.

[2] https://en.wikipedia.org/wiki/Time-Sensitive_Networking


> SO_TXTIME is in the ABI, and EDT has been used publicly in kernel
> patches and conference talks, e.g., Van Jacobson's Netdev 0x12
> keynote. Those are vendor agnostic commonly used terms.
> 

I agree that EDT (Earliest Departure Time) have become a thing and term
in our community.
We could associate this feature with this.
I do fear what hardware behavior will be it if I e.g. ask it to send a
packet 2 sec in the future on i225 which max support 1 sec.
Will hardware send it at 1 sec?
Because then I'm violating the *Earliest* Departure Time.


> But as long as Launch Time is not an Intel only trademark, fine to
> select that.

The IEEE 802.1Qbv is sometimes called Time-Aware Shaper (TAS), but I
don't like to for us to name this after this.  This features is simply
taking advantage of exposing one of the hardware building blocks
(controlling/setting packet "launch time") that can be used for
implementing a TAS.

I like the name "launch time" because it doesn't get easily confused
with other timestamps, and intuitively describes packet will be send at
a specific time (likely in future).

--Jesper