linux-kernel - Re: [PATCH RFC 0/4] Add XDP RX queue index metadata via kfuncs

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Message-ID: <87348a4yyd.fsf@cloudflare.com>
Date: Thu, 25 Sep 2025 12:18:50 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
Cc: davem@...emloft.net,  edumazet@...gle.com,  kuba@...nel.org,
  pabeni@...hat.com,  donald.hunter@...il.com,  andrew+netdev@...n.ch,
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  horms@...nel.org,  sdf@...ichev.me,  netdev@...r.kernel.org,
  linux-kernel@...r.kernel.org,  bpf@...r.kernel.org,
  linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH RFC 0/4] Add XDP RX queue index metadata via kfuncs

On Thu, Sep 25, 2025 at 11:54 AM +01, Mehdi Ben Hadj Khelifa wrote:
> On 9/25/25 10:43 AM, Jakub Sitnicki wrote:
>> On Tue, Sep 23, 2025 at 10:00 PM +01, Mehdi Ben Hadj Khelifa wrote:
>>>   This patch series is intended to make a base for setting
>>>   queue_index in the xdp_rxq_info struct in bpf/cpumap.c to
>>>   the right index. Although that part I still didn't figure
>>>   out yet,I m searching for my guidance to do that as well
>>>   as for the correctness of the patches in this series.
>> What is the use case/movtivation behind this work?
>
> The goal of the work is to have xdp programs have the correct packet RX queue
> index after being redirected through cpumap because currently the queue_index
> gets unset or more accurately set to 0 as a default in xdp_rxq_info. This is my
> current understanding.I still have to know how I can propogate that HW hint from
> the NICs to the function where I need it.

This explains what this series does, the desired end state of
information passing, but not why is does it - how that information is
going to be consumed? To what end?

I'd start by figuring that part out. Otherwise you're just proposing
adding code that serves no actual purpose.