linux-kernel - Re: [PATCH] bpf: cpumap: report Rx queue index to xdp_rxq

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Message-ID: <87msafcpkt.fsf@toke.dk>
Date: Tue, 10 Jun 2025 22:24:34 +0200
From: Toke Høiland-Jørgensen <toke@...nel.org>
To: Ujwal Kundur <ujwal.kundur@...il.com>, Alexander Lobakin
 <aleksander.lobakin@...el.com>
Cc: ast@...nel.org, daniel@...earbox.net, davem@...emloft.net,
 kuba@...nel.org, hawk@...nel.org, john.fastabend@...il.com,
 andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com,
 song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org,
 sdf@...ichev.me, aoluo@...gle.com, jolsa@...nel.org,
 netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: cpumap: report Rx queue index to xdp_rxq_info

Ujwal Kundur <ujwal.kundur@...il.com> writes:

>> This looks wrong...
>> I think this will always return index 0
>
>> So passing dev->_rx to that function will always return 0; which is what
>> the field is already initialised to...
>
> I didn't realize that would always return 0, sorry I should've tried
> to understand that statement better.
>
>> I'll just add that you may want to take a look at Lorenzo's series[0].
>> Rx queue index is sorta HW hint, so it shouldn't be a problem to add the
>> corresponding field to xdp_rx_meta.
>> Then, you can expand cpumap's code to try reading that HW meta if present.
>
> Thank you! I also tried to work backwards to figure out how the
> queue_index would be used if present in xdp_rxq_info but that wasn't
> immediately apparent to me.
> I'm keen on learning/contributing to the BPF part of the network stack
> and this seemed like a good first patch to take up -- I'll understand
> this better and try again.

Sounds good! Don't be discouraged by having to try again, that's
perfectly normal :)

-Toke