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    Subject[PATCH 02/18] sched: fix find_idlest_group mess logical
    Date
    There is 4 situations in the function:
    1, no task allowed group;
    so min_load = ULONG_MAX, this_load = 0, idlest = NULL
    2, only local group task allowed;
    so min_load = ULONG_MAX, this_load assigned, idlest = NULL
    3, only non-local task group allowed;
    so min_load assigned, this_load = 0, idlest != NULL
    4, local group + another group are task allowed.
    so min_load assigned, this_load assigned, idlest != NULL

    Current logical will return NULL in first 3 kinds of scenarios.
    And still return NULL, if idlest group is heavier then the
    local group in the 4th situation.

    Actually, I thought groups in situation 2,3 are also eligible to host
    the task. And in 4th situation, agree to bias toward local group.
    So, has this patch.

    Signed-off-by: Alex Shi <alex.shi@intel.com>
    ---
    kernel/sched/fair.c | 12 +++++++++---
    1 files changed, 9 insertions(+), 3 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index df99456..b40bc2b 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -2953,6 +2953,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
    int this_cpu, int load_idx)
    {
    struct sched_group *idlest = NULL, *group = sd->groups;
    + struct sched_group *this_group = NULL;
    unsigned long min_load = ULONG_MAX, this_load = 0;
    int imbalance = 100 + (sd->imbalance_pct-100)/2;

    @@ -2987,14 +2988,19 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,

    if (local_group) {
    this_load = avg_load;
    - } else if (avg_load < min_load) {
    + this_group = group;
    + }
    + if (avg_load < min_load) {
    min_load = avg_load;
    idlest = group;
    }
    } while (group = group->next, group != sd->groups);

    - if (!idlest || 100*this_load < imbalance*min_load)
    - return NULL;
    + if (this_group && idlest != this_group)
    + /* Bias toward our group again */
    + if (100*this_load < imbalance*min_load)
    + idlest = this_group;
    +
    return idlest;
    }

    --
    1.7.5.1


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