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

[Shubhang <sh@gentwo.org>]

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@gentwo.org>
> 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