Re: [PATCH v2] net/sched: sch_cake: skip redundant cake_mq rate updates

[Shubhang]

Hi Paolo,

On Thu, 29 Oct 2026, Paolo Abeni wrote:

> On 10/27/26 05:32, Shubhang Kaushik (Ampere) wrote:
> > cake_mq periodically counts active child qdiscs in cake_dequeue() and
> > derives an effective per-child shaper rate. cake_dequeue() currently
> > reconfigures every tin after each scan, even when that effective rate
> > is unchanged.
> >
> > The dequeue-time call chain is:
> >
> >    cake_dequeue()
> >      -> cake_configure_rates(..., true)
> >        -> cake_config_*()
> >          -> cake_set_rate()
> >
> > With rate_adjust=true, cake_set_rate() only refreshes rate-derived
> > state. Tin 0 records the unscaled rate argument in every supported
> > CAKE tin mode, so its installed rate identifies whether this call chain
> > would change any state.
> >
> > Skip the reconfiguration when the effective rate is already installed,
> > while continuing to update the activity-sampling timestamp and
> > active-queue statistic.
> >
> > Fixes: 1bddd758bac2 ("net/sched: sch_cake: share shaper state across 
> > sub-instances of cake_mq")
> > Signed-off-by: Shubhang Kaushik (Ampere) <sh@xxxxxxxxxx>
> IMHO this is borderline material for 'net'. Was any regression visible on
> top of 1bddd758bac2, e.g. in term of CPU usage?
>
> /P

Thanks for the feedback.

I repeated the test with whole-host CPU accounting on this 80-core system 
and could not measure a reliable aggregate CPU-use difference; throughput 
was unchanged. The benefit is visible in focused cake_configure_rates() 
trace, but I agree this is more appropriate for net-next.

Regards,
Shubhang Kaushik