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

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Message-ID: <e85e7bb2-6229-4b04-9c2a-7a7b79497c6c@gmail.com>
Date: Thu, 25 Sep 2025 12:28:07 +0100
From: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
To: Jakub Sitnicki <jakub@...udflare.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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 david.hunter.linux@...il.com, skhan@...uxfoundation.org, 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 9/25/25 11:18 AM, Jakub Sitnicki wrote:
> 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?

In my vision,The queue index propagated correctly through cpumap can 
help xdp programs use it for things such as per queue load 
balancing,Adaptive RSS tuning and even maybe for DDoS mitigation where 
they can drop traffic per queue.I mean if these aren't correct intents 
or if they don't justify the added code, I can abort working on it. Even 
if they weren't I need more guidance on how I can have that metadata 
from HW hints...
Best Regards,
Mehdi