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

[Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>]

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> 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?!?

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

> 
> /P
> 

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