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    Subject[RFC,v2 3/3] sched: ignore task_h_load for CPU_NEWLY_IDLE
    Date
    From: Uladzislau 2 Rezki <uladzislau2.rezki@sonymobile.com>

    A load balancer calculates imbalance factor for particular shed
    domain and tries to steal up the prescribed amount of weighted load.
    However, a small imbalance factor would sometimes prevent us from
    stealing any tasks at all. When a CPU is newly idle, it should
    steal first task which passes a migration criteria.

    Signed-off-by: Uladzislau 2 Rezki <uladzislau2.rezki@sonymobile.com>
    ---
    kernel/sched/fair.c | 13 +++++++++++--
    1 file changed, 11 insertions(+), 2 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 232ef3c..29e0d7f 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -6802,6 +6802,14 @@ static int detach_tasks(struct lb_env *env)
    if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1)
    break;

    + /*
    + * Another CPU can place tasks, since we do not hold dst_rq lock
    + * while doing balancing. If newly idle CPU already got something,
    + * give up to reduce latency.
    + */
    + if (env->idle == CPU_NEWLY_IDLE && env->dst_rq->nr_running > 0)
    + break;
    +
    p = list_first_entry(tasks, struct task_struct, se.group_node);

    env->loop++;
    @@ -6824,8 +6832,9 @@ static int detach_tasks(struct lb_env *env)
    if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed)
    goto next;

    - if ((load / 2) > env->imbalance)
    - goto next;
    + if (env->idle != CPU_NEWLY_IDLE)
    + if ((load / 2) > env->imbalance)
    + goto next;

    detach_task(p, env);
    list_add(&p->se.group_node, &env->tasks);
    --
    2.1.4
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