Re: [RFC net-next 0/5] Add ETS and TBF Qdisc offload for Airoha EN7581 SoC

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> Hi Lorenzo,

Hi Vladimir,

> 
> On Wed, Dec 11, 2024 at 04:31:48PM +0100, Lorenzo Bianconi wrote:
> > Introduce support for ETS and TBF qdisc offload available in the Airoha
> > EN7581 ethernet controller.
> > Some DSA hw switches do not support Qdisc offloading or the mac chip
> > has more fine grained QoS capabilities with respect to the hw switch
> > (e.g. Airoha EN7581 mac chip has more hw QoS and buffering capabilities
> > with respect to the mt7530 switch). 
> > Introduce ndo_setup_tc_conduit callback in order to allow tc to offload
> > Qdisc policies for the specified DSA user port configuring the hw switch
> > cpu port (mac chip).
> 
> Can you please make a detailed diagram explaining how is the conduit
> involved in the packet data path for QoS? Offloaded tc on a DSA user
> port is supposed to affect autonomously forwarded traffic too (like the
> Linux bridge).

I guess a typical use case would be the one below where the traffic from the
WAN port is forwarded to a DSA LAN one (e.g. lan0) via netfilter flowtable
offload.

            ┌─────────────────────────────────┐             
            │               BR0               │             
            └───┬────────┬────────┬────────┬──┘             
┌───────────────┼────────┼────────┼────────┼───┐            
│DSA            │        │        │        │   │            
│               │        │        │        │   │            
│ ┌───┐      ┌──▼─┐   ┌──▼─┐   ┌──▼─┐   ┌──▼─┐ │       ┌───┐
│ │CPU│      │LAN0│   │LAN1│   │LAN2│   │LAN3│ │       │WAN│
│ └───┘      └────┘   └────┘   └────┘   └────┘ │       └───┘
└──────────────────────────────────────────────┘            

In this case the mac chip forwards (in hw) the WAN traffic to the DSA switch
via the CPU port. In [0] we have the EN7581 mac chip architecture where we
can assume GDM1 is the CPU port and GDM2 is the WAN port.
The goal of this RFC series is to offload a Qdisc rule (e.g. ETS) on a given
LAN port using the mac chip QoS capabilities instead of creating the QoS
discipline directly in the DSA hw switch:

$tc qdisc replace dev lan0 root handle 1: ets bands 8 strict 2 quanta 1514 1514 1514 3528 1514 1514

As described above the reason for this approach would be to rely on the more
fine grained QoS capabilities available on the mac chip with respect to the
hw switch or because the DSA switch does not support QoS offloading.

Regards,
Lorenzo

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=23020f04932701d5c8363e60756f12b43b8ed752

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