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    SubjectRe: [PATCH 3/3 v2] sched/fair: reduce cases for active balance
    Date
    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.guittot@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;
    > +}
    > +

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