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

[Paolo Abeni <pabeni@redhat.com>]

On 10/8/26 17:31, Daniel Thompson wrote:
> On Tue, Oct 06, 2026 at 12:46:27PM +0200, Lorenzo Bianconi wrote:
>> 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?!?

/P