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

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Date:   Fri, 1 Dec 2023 16:39:32 +0100
From:   Jesper Dangaard Brouer <hawk@...nel.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "Song, Yoong Siang" <yoong.siang.song@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Bjorn Topel <bjorn@...nel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Mykola Lysenko <mykolal@...com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Andre Fredette <afredette@...hat.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "xdp-hints@...-project.net" <xdp-hints@...-project.net>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 0/3] xsk: TX metadata txtime support



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@...nel.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