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SubjectRe: [PATCH v3 04/10] sched/fair: rework load_balance
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On 9/19/19 1:03 PM, Vincent Guittot wrote:

[...]

> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> kernel/sched/fair.c | 585 ++++++++++++++++++++++++++++++++++------------------
> 1 file changed, 380 insertions(+), 205 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 017aad0..d33379c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7078,11 +7078,26 @@ static unsigned long __read_mostly max_load_balance_interval = HZ/10;
>
> enum fbq_type { regular, remote, all };
>
> +/*
> + * group_type describes the group of CPUs at the moment of the load balance.
> + * The enum is ordered by pulling priority, with the group with lowest priority
> + * first so the groupe_type can be simply compared when selecting the busiest
> + * group. see update_sd_pick_busiest().
> + */
> enum group_type {
> - group_other = 0,
> + group_has_spare = 0,
> + group_fully_busy,
> group_misfit_task,
> + group_asym_packing,
> group_imbalanced,
> - group_overloaded,
> + group_overloaded
> +};
> +
> +enum migration_type {
> + migrate_load = 0,
> + migrate_util,
> + migrate_task,
> + migrate_misfit
> };
>
> #define LBF_ALL_PINNED 0x01
> @@ -7115,7 +7130,7 @@ struct lb_env {
> unsigned int loop_max;
>
> enum fbq_type fbq_type;
> - enum group_type src_grp_type;
> + enum migration_type balance_type;
> struct list_head tasks;
> };
>
> @@ -7347,7 +7362,7 @@ static int detach_tasks(struct lb_env *env)
> {
> struct list_head *tasks = &env->src_rq->cfs_tasks;
> struct task_struct *p;
> - unsigned long load;
> + unsigned long util, load;
> int detached = 0;
>
> lockdep_assert_held(&env->src_rq->lock);
> @@ -7380,19 +7395,53 @@ static int detach_tasks(struct lb_env *env)
> if (!can_migrate_task(p, env))
> goto next;
>
> - load = task_h_load(p);
> + switch (env->balance_type) {
> + case migrate_load:
> + load = task_h_load(p);
>
> - if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
> - goto next;
> + if (sched_feat(LB_MIN) &&
> + load < 16 && !env->sd->nr_balance_failed)
> + goto next;
>
> - if ((load / 2) > env->imbalance)
> - goto next;
> + if ((load / 2) > env->imbalance)
> + goto next;
> +
> + env->imbalance -= load;
> + break;
> +
> + case migrate_util:
> + util = task_util_est(p);
> +
> + if (util > env->imbalance)

Can you please explain what would happen for
`if (util/2 > env->imbalance)` ?
just like when migrating load, even util shouldn't be migrated if
env->imbalance is just near the utilization of the task being moved, isn't it?

> + goto next;
> +
> + env->imbalance -= util;
> + break;
> +[ ... ]

Thanks,
Parth

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