Re: [PATCH] sched/idle: Prevent stopping the tick when there is no cpuidle driver

[Thomas Gleixner]

On Fri, Jan 12 2024 at 14:39, Pierre Gondois wrote:
> On 1/12/24 11:56, Anna-Maria Behnsen wrote:
>> Pierre Gondois <pierre.gondois@xxxxxxx> writes:
>>> I agree that the absence of cpuidle driver prevents from reaching deep
>>> idle states. FWIU, there is however still benefits in stopping the tick
>>> on such platform.
>> 
>> What's the benefit?
>
> I did the following test:
> - on an arm64 Juno-r2 platform (2 big A-72 and 4 little A-53 CPUs)
> - booting with 'cpuidle.off=1'
> - using the energy counters of the platforms
>    (the counters measure energy for the whole cluster of big/little CPUs)
> - letting the platform idling during 10s
>
> So the energy consumption would be up:
> - ~6% for the big CPUs
> - ~10% for the litte CPUs

Fair enough, but what's the actual usecase?

NOHZ w/o cpuidle driver seems a rather academic exercise to me.

Thanks,

        tglx