Re: [PATCH net-next v5 3/3] net: stmmac: add tc mqprio hw queue priority offload

On 10/8/26 17:31, Daniel Thompson wrote:

quoted

On Tue, Oct 06, 2026 at 12:46:27PM +0200, Lorenzo Bianconi wrote:

quoted

Implement the offload of the tc mqprio hw queue priority in the stmmac
driver. When the mqprio qdisc is configured in channel mode, the MTL TX
scheduler is switched to strict priority, and the PSTQX/PSTC priority
bitmask of each TX queue is programmed from the set of frame priorities
mapped to the owning traffic class (qopt->prio_tc_map).

The channel mode offload requires the DCB hw feature and a 1:1 TC to TX
queue mapping, with a single queue per TC. Configurations with AVB queues
are rejected, since forcing strict priority conflicts with the CBS
algorithm. The CBS offload is refused while the strict-priority scheduler
is active, and so is a channel count change that would enable an AVB
queue.

I don't think these CBS offload checks are necessary. It's quite reasonable
to mix strict priority on low priority queues with CBS on higher
priority queues.

In fact on the hardware I have (TC956x) the lower priority queues don't
implement CBS so mixing AVB and DCB queuing (whether SP or ETS) isn't
just reasonable, it's pretty much unavoidable when using CBS!

As a concrete example of combining mqprio and CBS, the following works well on
TC956x (when I tested an older version of your patch):

--- cut here ---

tc qdisc replace dev eth0 handle 100 parent root mqprio num_tc 4 \
     map  0  0  0  0  0  1  2  3  0  0  0  0  0  0  0  0 \
     queues 1@0 1@1 1@2 1@3 mode channel hw 1

# No CBS for TxQ1 means we can't offload this (h/ware stays in SP mode)
tc qdisc replace dev eth0 parent 100:2 handle 102: cbs \
     idleslope 800000 sendslope -1700000 hicredit 494 locredit -1049 \
     offload 0

tc qdisc replace dev eth0 parent 100:3 handle 103: cbs \
     idleslope 400000 sendslope -2100000 hicredit 247 locredit -1296 \
     offload 1

tc qdisc replace dev eth0 parent 100:4 handle 104: cbs \
     idleslope 200000 sendslope -2300000 hicredit 124 locredit -1419 \
     offload 1

--- cut here ---

Given your later tested-by, I assume you are looking for future possible
improvement?

Also it's not clear which revision you are referring to: AFAICS this
patch is (attempting to) refusing CBS + SP since v1?!?

Hi Paolo,

I fixed the issue reported by Daniel in [0]

Regards,
Lorenzo

[0] https://lore.kernel.org/netdev/20261012-stmmac-mqprio-cbs-combo-v1-1-831e323eb4ef@oss.qualcomm.com/T/#u (local)

/P