netdev - 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