linux-kernel - Re: [PATCH bpf-next v3 2/3] net: stmmac: add Launch Time support to XDP ZC

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Date:   Mon, 4 Dec 2023 11:36:30 +0100
From:   Jesper Dangaard Brouer <hawk@...nel.org>
To:     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>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <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>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, bpf@...r.kernel.org,
        xdp-hints@...-project.net,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 2/3] net: stmmac: add Launch Time support to
 XDP ZC

On 12/3/23 17:51, Song Yoong Siang wrote:
> This patch enables Launch Time (Time-Based Scheduling) support to XDP zero
> copy via XDP Tx metadata framework.
> 
> Signed-off-by: Song Yoong Siang<yoong.siang.song@...el.com>
> ---
>   drivers/net/ethernet/stmicro/stmmac/stmmac.h      |  2 ++

As requested before, I think we need to see another driver implementing 
this.

I propose driver igc and chip i225.

The interesting thing for me is to see how the LaunchTime max 1 second
into the future[1] is handled code wise. One suggestion is to add a 
section to Documentation/networking/xsk-tx-metadata.rst per driver that 
mentions/documents these different hardware limitations.  It is natural 
that different types of hardware have limitations.  This is a close-to 
hardware-level abstraction/API, and IMHO as long as we document the 
limitations we can expose this API without too many limitations for more 
capable hardware.

  [1] 
https://github.com/xdp-project/xdp-project/blob/master/areas/tsn/code01_follow_qdisc_TSN_offload.org#setup-code-driver-igb

This stmmac driver and Intel Tiger Lake CPU must also have some limit on 
how long into the future it will/can schedule packets?

People from xdp-hints list must make their voice hear if they want i210 
and igb driver support, because it have even-more hardware limitations, 
see [1] (E.g. only TX queue 0 and 1 supports LaunchTime). BUT I know 
some have this hardware in production and might be motivated to get a 
functioning driver with this feature?

--Jesper