From: <Daniel.Machon@microchip.com>
To: <vladimir.oltean@nxp.com>
Cc: <Allan.Nielsen@microchip.com>, <kuba@kernel.org>,
<petrm@nvidia.com>, <netdev@vger.kernel.org>,
<vinicius.gomes@intel.com>, <thomas.petazzoni@bootlin.com>,
<maxime.chevallier@bootlin.com>, <roopa@nvidia.com>
Subject: Re: Basic PCP/DEI-based queue classification
Date: Wed, 7 Sep 2022 19:57:08 +0000 [thread overview]
Message-ID: <Yxj5smlnHEMn0sq2@DEN-LT-70577> (raw)
In-Reply-To: <20220907172613.mufgnw3k5rt745ir@skbuf>
> On Wed, Sep 07, 2022 at 10:41:10AM +0000, Daniel.Machon@microchip.com wrote:
> > > 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).
>
> Not directly, but at least ocelot (or in fact felix) does set
> skb->priority based on the QoS class from the Extraction Frame Header.
> So the stack does end up consulting and meaningfully using something
> that was set based on the dcbnl APP table.
>
> In this sense, for ocelot, there is a real overlap between skb->priority
> being initially set based on ocelot_xfh_get_qos_class(), and later being
> overwritten based on the QoS maps of a VLAN interface.
Right, so VLAN QoS maps currently takes precedence, if somebody would choose
to add a tagged vlan interface on-top of a physical interface with existing
PCP prioritization - is this a real problem, or just a question of configuration?
> The problem with the ingress-qos-map and egress-qos-map from 802.1Q that
> I see is that they allow for per-VID prioritization, which is way more
> fine grained than what we need. This, plus the fact that bridge VLANs
> don't have this setting, only termination (8021q) VLANs do. How about an
> ingress-qos-map and an egress-qos-map per port rather than per VID,
> potentially even a bridge_slave netlink attribute, offloadable through
> switchdev? We could make the bridge input fast path alter skb->priority
> for the VLAN-tagged code paths, and this could give us superior
> semantics compared to putting this non-standardized knob in the hardware
> only dcbnl.
This is a valid alternative solution to dcbnl, although this seems to be a
much more complex solution, to something that is easily solved in dcbnl,
and actually is in-line with what dcbnl already does. On-top of this, the
notion of 'trust' has also been raised by this topic. It makes a lot of sense
to me to add APP selector trust and trust order to dcbnl. This is the solution
that I have been implementing lately, and is ready for posting very soon.
/ Daniel
next prev parent reply other threads:[~2022-09-07 19:57 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 9:09 Basic PCP/DEI-based queue classification Daniel.Machon
2022-08-19 10:50 ` Petr Machata
2022-08-21 20:58 ` Daniel.Machon
2022-08-22 10:34 ` Petr Machata
2022-08-24 7:39 ` Daniel.Machon
2022-08-24 9:45 ` Petr Machata
2022-08-24 17:55 ` Daniel.Machon
2022-08-24 19:36 ` Petr Machata
2022-08-25 0:54 ` Jakub Kicinski
2022-08-26 18:11 ` Petr Machata
2022-08-29 7:53 ` Allan W. Nielsen
2022-09-02 13:32 ` Vladimir Oltean
2022-09-07 10:41 ` Daniel.Machon
2022-09-07 17:26 ` Vladimir Oltean
2022-09-07 19:57 ` Daniel.Machon [this message]
2022-09-08 8:03 ` Allan Nielsen - M31684
2022-09-08 11:18 ` Petr Machata
2022-09-08 12:01 ` Daniel.Machon
2022-09-09 12:11 ` Vladimir Oltean
2022-09-08 8:27 ` Petr Machata
2022-08-25 11:31 ` Daniel.Machon
2022-08-25 13:30 ` Petr Machata
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