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

[Pierre Gondois]

Hello Thomas,

On 1/12/24 15:52, Thomas Gleixner wrote:
> 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.

I thought Anna-Maria had a use-case for this.
I just wanted to point out that this patch could potentially
increase the energy consumption for her use-case, nothing more,

Regards,
Pierre

> Thanks,
>
>          tglx