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

[Pierre Gondois <pierre.gondois@arm.com>]

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@arm.com> 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