netdev - Re: [PATCH] net: tsn: add an netlink interface between kernel and application layer

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Date:   Fri, 28 Dec 2018 11:29:56 -0800
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     PO LIU <po.liu@....com>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "davem\@davemloft.net" <davem@...emloft.net>,
        "haustad\@cisco.com" <haustad@...co.com>,
        "nicolas.ferre\@microchip.com" <nicolas.ferre@...rochip.com>,
        "gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
        Mingkai Hu <mingkai.hu@....com>, Roy Zang <roy.zang@....com>,
        PO LIU <po.liu@....com>, PO LIU <po.liu@....com>
Subject: Re: [PATCH] net: tsn: add an netlink interface between kernel and application layer

Hi,

PO LIU <po.liu@....com> writes:

> This patch provids netlink method to configure the TSN protocols hardwares.
> TSN guaranteed packet transport with bounded low latency, low packet delay
> variation, and low packet loss by hardware and software methods.

I don't think having another way to configure TSN features is a good
idea. We already have the CBS/ETF/taprio family of qdiscs, that provide
(or will in the near future, more on this later) a way to configure the
hardware.

A little background on the choice of qdiscs as an interface (and why we
came to believe they are a good abstraction), they already provide a way
to map packets into traffic classes (it isn't clear in our proposal how
you do that, but I think you are using something like mqprio), they
provide a neat way to "compose" (by installing one under another), they
already have a user facing API with various counters, and very
importantly for TSN they have mecanisms to offload some of their work to
the hardware.

I suggest is for you to take a look at how CBS offloading was
implemented for the Intel i210:

https://patchwork.ozlabs.org/cover/824626/

Patches 4 and 5 should be the interesting ones. I think you can use them
as inspiration for enabling CBS offload in your driver.

If you did take a look at those patches (and the current work that has
been upstreamed), my question then becomes, what are the reasons that it
might not work for your use cases?

>
> The three basic components of TSN are:
>
> 1. Time synchronization: This was implement by 8021AS which base on the
>    IEEE1588 precision Time Protocol. This is configured by the other way
>    in kernel.
>    8021AS not included in this patch.
>
> 2. Scheduling and traffic shaping and per-stream filter policing:
>    This patch support Qbv/Qci.

I am working on a proposal for the API for Qbv (and Qbu) offloading
using taprio. I should send it soon-ish. Your feedback would be very
welcome.

Also, how to expose in the qdiscs the per-stream filtering and policing
parts (Qci) is something that I don't know how to do right now, any
suggestions would be nice.

In short, take a look at what's there and see what's missing for the
stuff that you care about, then we can work on that.

>
> 3. Selection of communication paths:
>    This patch not support the pure software only TSN protocols(like Qcc)
>    but hardware related configuration.
>
> TSN Protocols supports by this patch: Qbv/Qci/Qbu/Credit-base Shaper(Qav).
> This patch verified on NXP ls1028ardb board.
>
> Will add more protocols in the future.
>
> Signed-off-by: Po Liu <Po.Liu@....com>

Cheers,
--
Vinicius