linux-kernel - Re: [Patch v6 4/7] sched/fair: Enable periodic update of average thermal pressure

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Date:   Tue, 17 Dec 2019 13:57:28 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Quentin Perret <qperret@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Thara Gopinath <thara.gopinath@...aro.org>, mingo@...hat.com,
        ionela.voinescu@....com, vincent.guittot@...aro.org,
        rui.zhang@...el.com, daniel.lezcano@...aro.org,
        viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
        amit.kachhap@...il.com, javi.merino@...nel.org,
        amit.kucheria@...durent.com
Subject: Re: [Patch v6 4/7] sched/fair: Enable periodic update of average
 thermal pressure

On 16/12/2019 18:59, Quentin Perret wrote:
> On Monday 16 Dec 2019 at 15:39:32 (+0100), Peter Zijlstra wrote:
>>> @@ -10274,6 +10281,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
>>>  
>>>  	update_misfit_status(curr, rq);
>>>  	update_overutilized_status(task_rq(curr));
>>> +	update_thermal_load_avg(rq_clock_task(rq), rq, thermal_pressure);
>>>  }
>>
>> My objection here is that when the arch does not have support for it,
>> there is still code generated and runtime overhead associated with it.
> 
> I guess this function could be stubbed for CONFIG_CPU_THERMAL=n ?
> That is, reflecting the thermal pressure in the scheduler only makes
> sense when the thermal infrastructure is enabled to begin with (which is
> indeed not the case for most archs).

Makes sense to me. If we can agree that 'CPU cooling' is the only actor
for thermal (CPU capacity) capping.

thermal_sys-$(CONFIG_CPU_THERMAL)       += cpu_cooling.o