netdev - Re: igc: AF_PACKET and SO

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Message-ID: <875xykalx0.fsf@kurt.kurt.home>
Date: Mon, 19 Feb 2024 09:38:35 +0100
From: Kurt Kanzenbach <kurt@...utronix.de>
To: Ferenc Fejes <ferenc.fejes@...csson.com>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>
Cc: "vinicius.gomes@...el.com" <vinicius.gomes@...el.com>, "hawk@...nel.org"
 <hawk@...nel.org>
Subject: Re: igc: AF_PACKET and SO_TXTIME question

Hi Ferenc,

On Fri Feb 16 2024, Ferenc Fejes wrote:
> We simply placed the ETF qdisc as the root qdisc and assumed that this
> would enable offload on all TX queues. Apparently this is not the case.
> According to the code, it was only enabled for queue 0. Another mistake
> we made is we used multiq qdisc with skbedit queue_mapping without
> bypass - which works since the tx action is executed.
> However, with qdisc baypass, the TX queue selection for the packets
> sent to the AF_PACKET socket looks like this
>
> tx_queue = cpu_id of task % num_tx_queues.
>
> With taskset, we were able to explicitly send packets to TX queue 0 in
> the bypass case, and that essentially solved the problem.
>
> So we switched to mqprio and enabled offloading on all queues and with
> that we always see the delayed packet transmission with launchtime
> enabled.

Glad it worked out. Thanks for sharing your solution!

Thanks,
Kurt

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