linux-kernel - Re: [PATCH v9 6/7] sched/fair: Remove task_util from effective utilization in feec()

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Message-ID: <Yp3JodkEgYUsQ4EV@google.com>
Date:   Mon, 6 Jun 2022 10:32:17 +0100
From:   Vincent Donnefort <vdonnefort@...gle.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, morten.rasmussen@....com,
        chris.redpath@....com, qperret@...gle.com, tao.zhou@...ux.dev,
        kernel-team@...roid.com
Subject: Re: [PATCH v9 6/7] sched/fair: Remove task_util from effective
 utilization in feec()

On Tue, May 31, 2022 at 10:17:01AM +0200, Dietmar Eggemann wrote:
> - Vincent Donnefort <vincent.donnefort@....com>
> 
> On 23/05/2022 17:51, Vincent Donnefort wrote:
> > From: Vincent Donnefort <vincent.donnefort@....com>
> 
> [...]
> 
> > @@ -6834,22 +6887,36 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
> >  	if (!task_util_est(p))
> >  		goto unlock;
> >  
> > +	eenv_task_busy_time(&eenv, p, prev_cpu);
> > +
> >  	for (; pd; pd = pd->next) {
> > -		unsigned long cur_delta, spare_cap, max_spare_cap = 0;
> > +		unsigned long cpu_cap, cpu_thermal_cap, util;
> > +		unsigned long cur_delta, max_spare_cap = 0;
> >  		bool compute_prev_delta = false;
> >  		unsigned long base_energy_pd;
> >  		int max_spare_cap_cpu = -1;
> >  
> >  		cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
> 
> Internal EAS testing of this patch-set version has revealed that this
> doesn't work against LTP CPU hotplug stress test. `struct cpumask *cpus`
> can't be used when it is empty. This can happen in case all PD CPUs are
> hotplugged out since we `and` the invariant PD cpumask with
> cpu_online_mask. We need a:
> 
> +               if (cpumask_empty(cpus))
> +                       continue;
> +
> 
> here.

Good catch, thanks for trying the test suite.

> 
> > -		for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) {
> > +		/* Account thermal pressure for the energy estimation */
> > +		cpu = cpumask_first(cpus);
> > +		cpu_thermal_cap = arch_scale_cpu_capacity(cpu);
> > +		cpu_thermal_cap -= arch_scale_thermal_pressure(cpu);
> 
> [...]