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

[Jesper Dangaard Brouer]

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@xxxxxxxxxx> 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