linux-kernel - Re: [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation helper function

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Date:   Fri, 6 Jul 2018 15:12:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joel@...lfernandes.org,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation
 helper function

On Thu, Jun 28, 2018 at 12:40:40PM +0100, Quentin Perret wrote:
> +static long 
   compute_energy(struct task_struct *p, int dst_cpu, struct freq_domain *fd)
> +{
> +	long util, max_util, sum_util, energy = 0;
> +	int cpu;
> +
> +	while (fd) {
> +		max_util = sum_util = 0;
> +		for_each_cpu_and(cpu, freq_domain_span(fd), cpu_online_mask) {

I had a wee little wtf moment when I realized this crosses root_domain
boundaries but that that is actually desired. A comment might be in
order.

> +			util = cpu_util_next(cpu, p, dst_cpu);
> +			util += cpu_util_dl(cpu_rq(cpu));
> +			/* XXX: add RT util_avg when available. */
> +
> +			max_util = max(util, max_util);
> +			sum_util += util;

Did you want to use sugov_get_util() here? There is no way we're going
to duplicate all that.

ISTR we already established the whole EAS was going to require using
schedutil anyway.

> +		}
> +
> +		energy += em_fd_energy(fd->obj, max_util, sum_util);
> +		fd = fd->next;
> +	}
> +
> +	return energy;
> +}