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SubjectRe: [RFC PATCH v2 4/6] sched/fair: Introduce an energy estimation helper function
On Fri, Apr 06, 2018 at 04:36:05PM +0100, Dietmar Eggemann wrote:

[...]

> +/*
> + * Estimates the system level energy assuming that p wakes-up on dst_cpu.
> + *
> + * compute_energy() is safe to call only if an energy model is available for
> + * the platform, which is when sched_energy_enabled() is true.
> + */
> +static unsigned long compute_energy(struct task_struct *p, int dst_cpu)
> +{
> + unsigned long util, max_util, sum_util;
> + struct capacity_state *cs;
> + unsigned long energy = 0;
> + struct freq_domain *fd;
> + int cpu;
> +
> + for_each_freq_domain(fd) {
> + max_util = sum_util = 0;
> + for_each_cpu_and(cpu, freq_domain_span(fd), cpu_online_mask) {
> + util = cpu_util_next(cpu, p, dst_cpu);
> + util += cpu_util_dl(cpu_rq(cpu));
> + max_util = max(util, max_util);
> + sum_util += util;
> + }
> +
> + /*
> + * Here we assume that the capacity states of CPUs belonging to
> + * the same frequency domains are shared. Hence, we look at the
> + * capacity state of the first CPU and re-use it for all.
> + */
> + cpu = cpumask_first(freq_domain_span(fd));
> + cs = find_cap_state(cpu, max_util);
> + energy += cs->power * sum_util / cs->cap;

I am a bit worry about the resolution issue, especially when the
capacity value is a quite high value and sum_util is a minor value.

> + }
> +
> + return energy;
> +}

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