linux-kernel - Re: [PATCH net-next 6/6] net/mlx5e: Support XDP target xmit with dummy program

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Message-ID: <893e8d23-121b-43ef-90a9-370a745d4341@gmail.com>
Date: Wed, 12 Nov 2025 13:28:05 +0200
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>,
 Tariq Toukan <tariqt@...dia.com>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Mark Bloch <mbloch@...dia.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, Gal Pressman <gal@...dia.com>,
 Leon Romanovsky <leonro@...dia.com>, Moshe Shemesh <moshe@...dia.com>,
 William Tu <witu@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>,
 Nimrod Oren <noren@...dia.com>, Alex Lazar <alazar@...dia.com>
Subject: Re: [PATCH net-next 6/6] net/mlx5e: Support XDP target xmit with
 dummy program

On 12/11/2025 12:29, Toke Høiland-Jørgensen wrote:
> Tariq Toukan <tariqt@...dia.com> writes:
> 
>> Save per-channel resources in default.
>>
>> As no better API exist, make the XDP-redirect-target SQ available by
>> loading a dummy XDP program.
> 
> This is a user-visible change, though, no? I.e., after this patch
> xdp_redirect mlx5 devices will no longer work as an xdp_redirect target
> out of the box?
> 

Right, we introduce an explicit behavior change here.
Due to the lack of a standard control, we're aligning to other drivers 
and use the dummy program trick.
Having the feature always on by default wastes HW and SW resources for 
users who are not interested in the feature (and cannot explicitly 
disable it), in addition to the significant extra latency it adds in 
configuration flow.

> We have userspace code listing the driver support in various places
> (e.g., here in xdp-tools:
> https://github.com/xdp-project/xdp-tools/commit/1dad1d6e0ccb086b8a31496931f21a165b42b700);
> I'm sure there will be other places. Since such code would up until now
> assume that mlx5 just works, this will end up being a regression in such
> cases, no?
> 
> -Toke
> 
> 

Yes, it is indeed a change in behavior.
Now the feature can be turned off, and actually defaults to off.
Now we should add "mlx5" to this list driver_pass_list[].