On Tue, Oct 07, 2014 at 02:13:36PM +0200, Vincent Guittot wrote:
> @@ -6214,17 +6178,21 @@ static inline void update_sd_lb_stats(struct lb_env 
> *env, struct sd_lb_stats *sd
>  
>               /*
>                * 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. We lower the capacity
>                * of a group only if the local group has the capacity to fit
> +              * these excess tasks, i.e. group_capacity > 0. The
>                * extra check prevents the case where you always pull from the
>                * heaviest group when it is already under-utilized (possible
>                * with a large weight task outweighs the tasks on the system).
>                */
>               if (prefer_sibling && sds->local &&
> +                 group_has_capacity(env, &sds->local_stat)) {
> +                     if (sgs->sum_nr_running > 1)
> +                             sgs->group_no_capacity = 1;
> +                     sgs->group_capacity = min(sgs->group_capacity,
> +                                             SCHED_CAPACITY_SCALE);
> +             }
>  
>               if (update_sd_pick_busiest(env, sds, sg, sgs)) {
>                       sds->busiest = sg;

> @@ -6490,8 +6460,8 @@ static struct sched_group *find_busiest_group(struct 
> lb_env *env)
>               goto force_balance;
>  
>       /* SD_BALANCE_NEWIDLE trumps SMP nice when underutilized */
> -     if (env->idle == CPU_NEWLY_IDLE && local->group_has_free_capacity &&
> -         !busiest->group_has_free_capacity)
> +     if (env->idle == CPU_NEWLY_IDLE && group_has_capacity(env, local) &&
> +         busiest->group_no_capacity)
>               goto force_balance;
>  
>       /*

This is two calls to group_has_capacity() on the local group. Why not
compute once in update_sd_lb_stats()?
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