netdev - Re: [PATCH net-next v3 2/8] taprio: Add support for frame preemption offload

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Message-ID: <20210129232015.atl4336zqy4ev3bi@skbuf>
Date:   Fri, 29 Jan 2021 23:20:16 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>,
        Po Liu <po.liu@....com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>
Subject: Re: [PATCH net-next v3 2/8] taprio: Add support for frame preemption
 offload

On Fri, Jan 29, 2021 at 01:13:24PM -0800, Vinicius Costa Gomes wrote:
> > Secondly, why should at least one queue be preemptible? What's wrong
> > with frame preemption being triggered by a tc-taprio window smaller than
> > the packet size? This can happen regardless of traffic class.
>
> It's the opposite, at least one queue needs to be marked
> express/non-preemptible.

I meant to ask why should at least one queue be express. The second part
of the question remains valid.

> But as I said above, perhaps this should be handled in a per-driver
> way. I will remove this from taprio.
>
> I think removing this check/limitation from taprio should solve the
> second part of your question, right?

Nope. Can you point me to either 802.1Q or 802.3 saying that at least
one priority should go to the express MAC?