Re: [PATCH net-next v7 2/2] net: dsa: mv88e6xxx: add support for credit based shaper

[Luke Howard]

> Are DSA ports multi-queue? I would have expected a DSA driver to
> offload PRIO not MQPRIO.

(Noting that the example did not offload the MQPRIO Qdisc –)

Some Marvell switches do have multiple TX queues, but a flexible mapping from PCP/DSCP values is configurable only on ingress. Cedric has a separate patch to do this via DCB APP for PCP. These mappings are global on the 6352 family and per-port on the 6390.

On egress, one can use the switch chips’ AVB support, but this limits the number of TCs to three (corresponding to SR class A, B, and ‘legacy’ traffic). I have a submitted MQPRIO offload patch that does this. This matches how MQPRIO and CBS are used on end station NICs, but is not flexible enough to support an arbitrary number of TCs. Because of this, offloading PRIO may be cleaner.

Luke