Re: [RFCv5 PATCH 32/46] sched: Energy-aware wake-up task placement

Sai Gurrappadi
2015-07-17T00:12:13Z

Hi Morten,

On 07/07/2015 11:24 AM, Morten Rasmussen wrote:
> ---

> +static int energy_aware_wake_cpu(struct task_struct *p, int target)
> +{
> + struct sched_domain *sd;
> + struct sched_group *sg, *sg_target;
> + int target_max_cap = INT_MAX;
> + int target_cpu = task_cpu(p);
> + int i;
> +
> + sd = rcu_dereference(per_cpu(sd_ea, task_cpu(p)));
> +
> + if (!sd)
> + return target;
> +
> + sg = sd->groups;
> + sg_target = sg;
> +
> + /*
> + * Find group with sufficient capacity. We only get here if no cpu is
> + * overutilized. We may end up overutilizing a cpu by adding the task,
> + * but that should not be any worse than select_idle_sibling().
> + * load_balance() should sort it out later as we get above the tipping
> + * point.
> + */
> + do {
> + /* Assuming all cpus are the same in group */
> + int max_cap_cpu = group_first_cpu(sg);
> +
> + /*
> + * Assume smaller max capacity means more energy-efficient.
> + * Ideally we should query the energy model for the right
> + * answer but it easily ends up in an exhaustive search.
> + */
> + if (capacity_of(max_cap_cpu) < target_max_cap &&
> + task_fits_capacity(p, max_cap_cpu)) {
> + sg_target = sg;
> + target_max_cap = capacity_of(max_cap_cpu);
> + }
> + } while (sg = sg->next, sg != sd->groups);

Should be capacity_orig_of(max_cap_cpu) right? Might select a suboptimal
sg_target if max_cap_cpu has a significant amount of IRQ/RT activity.

> +
> + /* Find cpu with sufficient capacity */
> + for_each_cpu_and(i, tsk_cpus_allowed(p), sched_group_cpus(sg_target)) {
> + /*
> + * p's blocked utilization is still accounted for on prev_cpu
> + * so prev_cpu will receive a negative bias due the double
> + * accouting. However, the blocked utilization may be zero.
> + */
> + int new_usage = get_cpu_usage(i) + task_utilization(p);
> +
> + if (new_usage > capacity_orig_of(i))
> + continue;

Is this supposed to be capacity_of(i) instead?

> +
> + if (new_usage < capacity_curr_of(i)) {
> + target_cpu = i;
> + if (cpu_rq(i)->nr_running)
> + break;
> + }
> +
> + /* cpu has capacity at higher OPP, keep it as fallback */
> + if (target_cpu == task_cpu(p))
> + target_cpu = i;
> + }
> +
> + if (target_cpu != task_cpu(p)) {
> + struct energy_env eenv = {
> + .usage_delta = task_utilization(p),
> + .src_cpu = task_cpu(p),
> + .dst_cpu = target_cpu,
> + };
> +
> + /* Not enough spare capacity on previous cpu */
> + if (cpu_overutilized(task_cpu(p)))
> + return target_cpu;
> +
> + if (energy_diff(&eenv) >= 0)
> + return task_cpu(p);
> + }
> +
> + return target_cpu;
> +}
> +

-Sai