On 07/01/21 11:33, Vincent Guittot wrote:
> Active balance is triggered for a number of voluntary cases like misfit
> or pinned tasks cases but also after that a number of load balance
> attempts failed to migrate a task. There is no need to use active load
> balance when the group is overloaded because an overloaded state means
> that there is at least one waiting task. Nevertheless, the waiting task
> is not selected and detached until the threshold becomes higher than its
> load. This threshold increases with the number of failed lb (see the
> condition if ((load >> env->sd->nr_balance_failed) > env->imbalance) in
> detach_tasks()) and the waiting task will end up to be selected after a
> number of attempts.
>
> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
> ---
> kernel/sched/fair.c | 45 +++++++++++++++++++++++----------------------
> 1 file changed, 23 insertions(+), 22 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a3515dea1afc..00ec5b901188 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9499,13 +9499,32 @@ asym_active_balance(struct lb_env *env)
> }
>
> static inline bool
> -voluntary_active_balance(struct lb_env *env)
> +imbalanced_active_balance(struct lb_env *env)
> +{
> + struct sched_domain *sd = env->sd;
> +
> + /*
> + * The imbalanced case includes the case of pinned tasks preventing a
> fair
> + * distribution of the load on the system but also the even
> distribution of the
> + * threads on a system with spare capacity
> + */
Do you mean s/imbalanced/migrate_task/? This part here will affect
group_imbalanced, group_asym_packing, and some others.
> + if ((env->migration_type == migrate_task) &&
> + (sd->nr_balance_failed > sd->cache_nice_tries+2))
> + return 1;
> +
> + return 0;
> +}
> +
