Re: [very-RFC 0/8] TSN driver for the kernel

Henrik Austad
2016-06-14T08:36:01Z

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On Mon, Jun 13, 2016 at 08:56:44AM -0700, John Fastabend wrote:
> On 16-06-13 04:47 AM, Richard Cochran wrote:
> > [...]
> > Here is what is missing to support audio TSN:
> >
> > * User Space
> >
> > 1. A proper userland stack for AVDECC, MAAP, FQTSS, and so on. The
> > OpenAVB project does not offer much beyond simple examples.
> >
> > 2. A user space audio application that puts it all together, making
> > use of the services in #1, the linuxptp gPTP service, the ALSA
> > services, and the network connections. This program will have all
> > the knowledge about packet formats, AV encodings, and the local HW
> > capabilities. This program cannot yet be written, as we still need
> > some kernel work in the audio and networking subsystems.
> >
> > * Kernel Space
> >
> > 1. Providing frames with a future transmit time. For normal sockets,
> > this can be in the CMESG data. For mmap'ed buffers, we will need a
> > new format. (I think Arnd is working on a new layout.)
> >
> > 2. Time based qdisc for transmitted frames. For MACs that support
> > this (like the i210), we only have to place the frame into the
> > correct queue. For normal HW, we want to be able to reserve a time
> > window in which non-TSN frames are blocked. This is some work, but
> > in the end it should be a generic solution that not only works
> > "perfectly" with TSN HW but also provides best effort service using
> > any NIC.
> >
>
> When I looked at this awhile ago I convinced myself that it could fit
> fairly well into the DCB stack (DCB is also part of 802.1Q). A lot of
> the traffic class to queue mappings and priories could be handled here.
> It might be worth taking a look at ./net/sched/mqprio.c and ./net/dcb/.

Interesting, I'll have a look at dcb and mqprio, I'm not familiar with
those systems. Thanks for pointing those out!

I hope that the complexity doesn't run crazy though, TSN is not aimed at
datacentra, a lot of the endpoints are going to be embedded devices,
introducing a massive stack for handling every eventuality in 802.1q is
going to be counter productive.

> Unfortunately I didn't get too far along but we probably don't want
> another mechanism to map hw queues/tcs/etc if the existing interfaces
> work or can be extended to support this.

Sure, I get that, as long as the complexity for setting up a link doesn't
go through the roof :)

Thanks!

--
Henrik Austad

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