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SubjectRe: [PATCH v3 04/10] sched/fair: rework load_balance
group_asym_packing

On Tue, 1 Oct 2019 at 10:15, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
> On 19/09/2019 09:33, Vincent Guittot wrote:
>
>
> [...]
>
> > @@ -8042,14 +8104,24 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> > }
> > }
> >
> > - /* Adjust by relative CPU capacity of the group */
> > + /* Check if dst cpu is idle and preferred to this group */
> > + if (env->sd->flags & SD_ASYM_PACKING &&
> > + env->idle != CPU_NOT_IDLE &&
> > + sgs->sum_h_nr_running &&
> > + sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) {
> > + sgs->group_asym_packing = 1;
> > + }
> > +
>
> Since asym_packing check is done per-sg rather per-CPU (like misfit_task), can you
> not check for asym_packing in group_classify() directly (like for overloaded) and
> so get rid of struct sg_lb_stats::group_asym_packing?

asym_packing uses a lot of fields of env to set group_asym_packing but
env is not statistics and i'd like to remove env from
group_classify() argument so it will use only statistics.
At now, env is an arg of group_classify only for imbalance_pct field
and I have replaced env by imabalnce_pct in a patch that is under
preparation.
With this change, I can use group_classify outside load_balance()

>
> Something like (only compile tested).
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d0c3aa1dc290..b2848d6f8a2a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7692,7 +7692,6 @@ struct sg_lb_stats {
> unsigned int idle_cpus;
> unsigned int group_weight;
> enum group_type group_type;
> - unsigned int group_asym_packing; /* Tasks should be moved to preferred CPU */
> unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */
> #ifdef CONFIG_NUMA_BALANCING
> unsigned int nr_numa_running;
> @@ -7952,6 +7951,20 @@ group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
> return false;
> }
>
> +static inline bool
> +group_has_asym_packing(struct lb_env *env, struct sched_group *sg,
> + struct sg_lb_stats *sgs)
> +{
> + if (env->sd->flags & SD_ASYM_PACKING &&
> + env->idle != CPU_NOT_IDLE &&
> + sgs->sum_h_nr_running &&
> + sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
> + return true;
> + }
> +
> + return false;
> +}
> +
> /*
> * group_smaller_min_cpu_capacity: Returns true if sched_group sg has smaller
> * per-CPU capacity than sched_group ref.
> @@ -7983,7 +7996,7 @@ group_type group_classify(struct lb_env *env,
> if (sg_imbalanced(group))
> return group_imbalanced;
>
> - if (sgs->group_asym_packing)
> + if (group_has_asym_packing(env, group, sgs))
> return group_asym_packing;
>
> if (sgs->group_misfit_task_load)
> @@ -8076,14 +8089,6 @@ static inline void update_sg_lb_stats(struct lb_env *env,
> }
> }
>
> - /* Check if dst cpu is idle and preferred to this group */
> - if (env->sd->flags & SD_ASYM_PACKING &&
> - env->idle != CPU_NOT_IDLE &&
> - sgs->sum_h_nr_running &&
> - sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) {
> - sgs->group_asym_packing = 1;
> - }
> -
> sgs->group_capacity = group->sgc->capacity;
>
> [...]

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