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SubjectRe: [PATCH 3/4] sched: drop group_capacity to 1 only if local group has extra capacity
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On Fri, 2010-10-15 at 09:13 -0700, Nikhil Rao wrote:

> >> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> >> index 0dd1021..da0c688 100644
> >> --- a/kernel/sched_fair.c
> >> +++ b/kernel/sched_fair.c
> >> @@ -2030,6 +2030,7 @@ struct sd_lb_stats {
> >> unsigned long this_load;
> >> unsigned long this_load_per_task;
> >> unsigned long this_nr_running;
> >> + unsigned long this_group_capacity;
> >>
> >> /* Statistics of the busiest group */
> >> unsigned long max_load;
> >> @@ -2546,15 +2547,18 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
> >> /*
> >> * In case the child domain prefers tasks go to siblings
> >> * first, lower the sg capacity to one so that we'll try
> >> - * and move all the excess tasks away.
> >> + * and move all the excess tasks away. We lower capacity only
> >> + * if the local group can handle the extra capacity.
> >> */
> >> - if (prefer_sibling)
> >> + if (prefer_sibling && !local_group &&
> >> + sds->this_nr_running < sds->this_group_capacity)
> >> sgs.group_capacity = min(sgs.group_capacity, 1UL);
> >>
> >> if (local_group) {
> >> sds->this_load = sgs.avg_load;
> >> sds->this = sg;
> >> sds->this_nr_running = sgs.sum_nr_running;
> >> + sds->this_group_capacity = sgs.group_capacity;
> >> sds->this_load_per_task = sgs.sum_weighted_load;
> >> } else if (update_sd_pick_busiest(sd, sds, sg, &sgs, this_cpu)) {
> >> sds->max_load = sgs.avg_load;

OK, but then you assume that local_group will always be the first group
served, nor is there any purpose for adding sds->this_group_capacity,
you could keep that local to this function.

For regular balancing local_group will be the first, since we only
ascend the domain tree on the local groups. But its not true for no_hz
balancing afaikt.




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