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

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Message-ID: <CALkFLLJpz2MxRZ8r+mGayU_BZE=2=ukXTzXcnmyhXeHB7Q6v3g@mail.gmail.com>
Date: Tue, 10 Jun 2025 19:32:37 +0530
From: Ujwal Kundur <ujwal.kundur@...il.com>
To: 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

> 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.

Thanks for your time,
Ujwal