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    Subject[PATCH 2/2] sched: fix a logical error in select_task_rq_fair
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    If find_idlest_cpu() return '-1', and sd->child is NULL. The function
    select_task_rq_fair will return -1. That is not the function's purpose.

    The patch introduced a latest_cpu as temporay varible to store
    find_idlest_cpu() return value, and let new_cpu to store the latest
    workable cpu. If find_idlest_cpu() doesn't find idlest cpu, we still
    have a latest workable cpu.

    Signed-off-by: Alex Shi <alex.shi@intel.com>
    ---
    kernel/sched/fair.c | 9 +++++++--
    1 files changed, 7 insertions(+), 2 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 8a1db69..7e4bab48 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -2730,6 +2730,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
    int load_idx = sd->forkexec_idx;
    struct sched_group *group;
    int weight;
    + int latest_cpu;

    if (!(sd->flags & sd_flag)) {
    sd = sd->child;
    @@ -2745,8 +2746,12 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
    continue;
    }

    - new_cpu = find_idlest_cpu(group, p, cpu);
    - if (new_cpu == -1 || new_cpu == cpu) {
    + latest_cpu = find_idlest_cpu(group, p, cpu);
    +
    + if (latest_cpu != -1)
    + new_cpu = latest_cpu;
    +
    + if (latest_cpu == -1 || latest_cpu == cpu) {
    /* Now try balancing at a lower domain level of cpu */
    sd = sd->child;
    continue;
    --
    1.7.5.4


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