netdev - Re: [RFC PATCH net-next 1/2] net: dsa: allow setting port-based QoS priority using tc matchall skbedit

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Date:   Fri, 11 Feb 2022 17:08:49 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Petr Machata <petrm@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Ido Schimmel <idosch@...dia.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...dia.com>, f.fainelli@...il.com,
        vivien.didelot@...il.com
Subject: Re: [RFC PATCH net-next 1/2] net: dsa: allow setting port-based QoS
 priority using tc matchall skbedit

> > Now I don't understand DSA at all, but given a chip with fancy defaults,
> > for the DCB interface in particular, it would make sense to me to have
> > two ops. As long as there are default-prio entries, a "set default
> > priority" op would get invoked with the highest configured default
> > priority. When the last entry disappears, an "unset" op would be called.
> 
> I don't understand this comment, sorry. I don't know what's a "chip with
> fancy defaults".

I think this is the point i just razed in my other reply. The hardware
starts with a preconfigured QoS profile. My guess would be, a Top Of
Rack defaults to all QoS features turned off, you need to turn them
off as appropriate for the use case. Typically, a SOHO switch is not
configured, it is just put in the corner and turned on. So having some
sensible defaults for a home/office makes sense. When it is used in
some other embedded use case, it probably is going to get configured
for that use cases.

So 'fancy defaults' == preconfigured QoS profile in the hardware.

    Andrew