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Date:   Fri, 17 Jan 2020 11:40:45 +0000
From:   Quentin Perret <qperret@google.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Thara Gopinath <thara.gopinath@linaro.org>, mingo@redhat.com,
        ionela.voinescu@arm.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rui.zhang@intel.com,
        daniel.lezcano@linaro.org, viresh.kumar@linaro.org,
        linux-kernel@vger.kernel.org, amit.kachhap@gmail.com,
        javi.merino@kernel.org, amit.kucheria@verdurent.com,
        kernel-team@android.com
Subject: Re: [Patch v8 4/7] sched/fair: Enable periodic update of average
 thermal pressure
Message-ID: <20200117114045.GA219309@google.com>
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 <20200116151502.GQ2827@hirez.programming.kicks-ass.net>
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On Thursday 16 Jan 2020 at 16:15:02 (+0100), Peter Zijlstra wrote:
> > @@ -10275,6 +10281,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
> >  {
> >  	struct cfs_rq *cfs_rq;
> >  	struct sched_entity *se = &curr->se;
> > +	unsigned long thermal_pressure = arch_cpu_thermal_pressure(cpu_of(rq));
> >  
> >  	for_each_sched_entity(se) {
> >  		cfs_rq = cfs_rq_of(se);
> > @@ -10286,6 +10293,7 @@ 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);
> >  }
> 
> I'm thinking this is the wrong place; should this not be in
> scheduler_tick(), right before calling sched_class::task_tick() ? Surely
> any execution will affect thermals, not only fair class execution.

Right, but right now only CFS takes action when we overheat. That is,
only CFS uses capacity_of() which is where the thermal signal gets
reflected.

We definitely could (and maybe should) make RT and DL react to thermal
pressure as well when they're both capacity-aware. But perhaps that's
for later ? Thoughts ?

Thanks,
Quentin