On 12/09/16 08:47, Vincent Guittot wrote:
> When a task moves from/to a cfs_rq, we set a flag which is then used to
> propagate the change at parent level (sched_entity and cfs_rq) during
> next update. If the cfs_rq is throttled, the flag will stay pending until
> the cfs_rw is unthrottled.
>
> For propagating the utilization, we copy the utilization of child cfs_rq to
s/child/group ?
> the sched_entity.
>
> For propagating the load, we have to take into account the load of the
> whole task group in order to evaluate the load of the sched_entity.
> Similarly to what was done before the rewrite of PELT, we add a correction
> factor in case the task group's load is less than its share so it will
> contribute the same load of a task of equal weight.
What about cfs_rq->runnable_load_avg?
[...]
> +/* Take into account change of load of a child task group */
> +static inline void
> +update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se)
> +{
> + struct cfs_rq *gcfs_rq = group_cfs_rq(se);
> + long delta, load = gcfs_rq->avg.load_avg;
> +
> + /* If the load of group cfs_rq is null, the load of the
> + * sched_entity will also be null so we can skip the formula
> + */
> + if (load) {
> + long tg_load;
> +
> + /* Get tg's load and ensure tg_load > 0 */
> + tg_load = atomic_long_read(&gcfs_rq->tg->load_avg) + 1;
> +
> + /* Ensure tg_load >= load and updated with current load*/
> + tg_load -= gcfs_rq->tg_load_avg_contrib;
> + tg_load += load;
> +
> + /* scale gcfs_rq's load into tg's shares*/
> + load *= scale_load_down(gcfs_rq->tg->shares);
> + load /= tg_load;
> +
> + /*
> + * we need to compute a correction term in the case that the
> + * task group is consuming <1 cpu so that we would contribute
> + * the same load as a task of equal weight.
Wasn't 'consuming <1' related to 'NICE_0_LOAD' and not
scale_load_down(gcfs_rq->tg->shares) before the rewrite of PELT (v4.2,
__update_group_entity_contrib())?
> + */
> + if (tg_load < scale_load_down(gcfs_rq->tg->shares)) {
> + load *= tg_load;
> + load /= scale_load_down(gcfs_rq->tg->shares);
> + }
> + }
[...]
