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

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Date:   Mon, 16 Dec 2019 17:59:01 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     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 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).

Thanks,
Quentin