netdev - Re: Basic PCP/DEI-based queue classification

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Date:   Wed, 7 Sep 2022 10:41:10 +0000
From:   <Daniel.Machon@...rochip.com>
To:     <vladimir.oltean@....com>
CC:     <Allan.Nielsen@...rochip.com>, <kuba@...nel.org>,
        <petrm@...dia.com>, <netdev@...r.kernel.org>,
        <vinicius.gomes@...el.com>, <thomas.petazzoni@...tlin.com>,
        <maxime.chevallier@...tlin.com>, <roopa@...dia.com>
Subject: Re: Basic PCP/DEI-based queue classification

> > I think this feature belong in DCB simply because DCB already have the
> > related configurations (like the default prio, priority-flow-control
> > etc), and it will be more logical for the user to find the PCP mapping
> > in the same place.
> >
> > I think that framepreemption should be in ethtool as it is partly
> > defined in IEEE802.3 (the physical layer) and it is ethernet only
> > technology.
> >
> > /Allan
> 
> My explanation given to Jakub at the time was that I don't quite
> understand what should belong to dcbnl and what shouldn't.
> https://lore.kernel.org/netdev/20220523224943.75oyvbxmyp2kjiwi@skbuf/
> 
> From my perspective it's an inconvenience that dcbnl exists as a
> separate kernel subsystem and isn't converged with the ethtool
> genetlink.
> 
> Regarding the topic at hand, and the apparent lack of PCP-based
> prioritization in the software data path. VLAN devices have an
> ingress-qos-map and an egress-qos-map. How would prioritization done via
> dcbnl interact with those (who would take precedence)?

Hi Vladimir,

They shouldn't interact (at least this is my understanding). 

The ingress and egress maps are for vlan interfaces, and dcb operates
on physical interfaces (dcbx too). You cannot use dcbnl to do
prioritization for vlan interfaces.

Anyway, I think much of the stuff in DCB is for hw offload only, incl. the
topic at hand. Is the APP table even consulted by the sw stack at all - I
dont think so (apart from drivers).

/ Daniel