Re: Questions regarding AF_XDP (ETF, TX queue selection) - Toke Høiland-Jørgensen

From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: "Deric, Nemanja" <nemanja.deric@siemens.com>,
	"xdp-newbies@vger.kernel.org" <xdp-newbies@vger.kernel.org>
Cc: "Bezdeka, Florian" <florian.bezdeka@siemens.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>
Subject: Re: Questions regarding AF_XDP (ETF, TX queue selection)
Date: Sat, 09 Apr 2022 15:00:40 +0200	[thread overview]
Message-ID: <878rse8l8n.fsf@toke.dk> (raw)
In-Reply-To: <DB6PR10MB1558DC7F6B10FD08418EC505EAE99@DB6PR10MB1558.EURPRD10.PROD.OUTLOOK.COM>

"Deric, Nemanja" <nemanja.deric@siemens.com> writes:

> Dear XDP-newbies,
>
> I am Nemanja Deric, and I am working as a Researcher for Industrial 
> Networking Department of Siemens AG (Munich, Germany). Recently, 
> we have started looking into AF_XDP/XDP and its applicability for some 
> of our industrial use cases. Thus, we have a few questions about the 
> technology which we hope that this mailing list can help us clarify.
>
> If you believe that these questions are better suited for some other 
> mailing list or direct email contact, please let me know so that I can 
> contact the correct person/mailing list.
>
> ETF, Timestamping:
> In comparison to AF_PACKET sockets AF_XDP sockets do not support 
> timestamping (SOL_TXTIME) yet. There seems no way to pass such 
> request or meta-information to the kernel / NIC. Is that correct? We 
> already heard about "xdp hints" but we have failed to get further 
> information like plans / roadmap / implementation state / ideas. 
> Any pointers where to look at?

Your understanding is basically correct: there's currently no support
for that kind of metadata in XDP at all (which extends to AF_XDP). The
effort to fix that is xdp-hints, and timestamps are explicitly part of
that. That's still work in progress; there's a mailing list dedicated
to this that you may want to subscribe to (and feel free to send a
message there indicating your interest!):

https://lists.xdp-project.net/postorius/lists/xdp-hints.xdp-project.net/

The closest you can get to a "progress report" is probably looking
through the archive of that list.

> TX queue selection:
> AF_XDP sockets are always bound to a specific RX queue. Instead, 
> TX queues are "automatically" chosen by the kernel - TX is more or 
> less handled by NAPI. Correct? Has someone already thought about 
> TX queue selection? Any plans / roadmap / details according 
> implementation state available?

+Magnus who may have an idea about this.

-Toke