netdev - Re: [next-queue RFC 0/4] ethtool: Add support for frame preemption

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Date:   Mon, 18 May 2020 12:05:04 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     David Miller <davem@...emloft.net>, olteanv@...il.com
Cc:     intel-wired-lan@...ts.osuosl.org, jeffrey.t.kirsher@...el.com,
        netdev@...r.kernel.org, vladimir.oltean@....com, po.liu@....com,
        m-karicheri2@...com, Jose.Abreu@...opsys.com
Subject: Re: [next-queue RFC 0/4] ethtool: Add support for frame preemption

Hi,

David Miller <davem@...emloft.net> writes:

> From: Vladimir Oltean <olteanv@...il.com>
> Date: Sun, 17 May 2020 00:03:39 +0300
>
>> As to why this doesn't go to tc but to ethtool: why would it go to tc?
>
> Maybe you can't %100 duplicate the on-the-wire special format and
> whatever, but the queueing behavior ABSOLUTELY you can emulate in
> software.

Just saying what Vladimir said in different words: the queueing behavior
is already implemented in software, by mqprio or taprio, for example.

That is to say, if we add frame preemption support to those qdiscs all
they will do is pass the information to the driver, and that's it. They
won't be able to use that information at all.

The mental model I have for this feature is that is more similar to the
segmentation offloads, energy efficient ethernet or auto-negotiation
than it is to a traffic shaper like CBS.

>
> And then you have the proper hooks added for HW offload which can
> do the on-the-wire stuff.
>
> That's how we do these things, not with bolted on ethtool stuff.

Cheers,
-- 
Vinicius