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    Subject[PATCH v4 01/11] sched/fair: clean up asym packing
    Date
    Clean up asym packing to follow the default load balance behavior:
    - classify the group by creating a group_asym_packing field.
    - calculate the imbalance in calculate_imbalance() instead of bypassing it.

    We don't need to test twice same conditions anymore to detect asym packing
    and we consolidate the calculation of imbalance in calculate_imbalance().

    There is no functional changes.

    Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
    Acked-by: Rik van Riel <riel@surriel.com>
    ---
    kernel/sched/fair.c | 63 ++++++++++++++---------------------------------------
    1 file changed, 16 insertions(+), 47 deletions(-)

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 1f0a5e1..617145c 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -7675,6 +7675,7 @@ struct sg_lb_stats {
    unsigned int group_weight;
    enum group_type group_type;
    int group_no_capacity;
    + unsigned int group_asym_packing; /* Tasks should be moved to preferred CPU */
    unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */
    #ifdef CONFIG_NUMA_BALANCING
    unsigned int nr_numa_running;
    @@ -8129,9 +8130,17 @@ static bool update_sd_pick_busiest(struct lb_env *env,
    * ASYM_PACKING needs to move all the work to the highest
    * prority CPUs in the group, therefore mark all groups
    * of lower priority than ourself as busy.
    + *
    + * This is primarily intended to used at the sibling level. Some
    + * cores like POWER7 prefer to use lower numbered SMT threads. In the
    + * case of POWER7, it can move to lower SMT modes only when higher
    + * threads are idle. When in lower SMT modes, the threads will
    + * perform better since they share less core resources. Hence when we
    + * have idle threads, we want them to be the higher ones.
    */
    if (sgs->sum_nr_running &&
    sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
    + sgs->group_asym_packing = 1;
    if (!sds->busiest)
    return true;

    @@ -8273,51 +8282,6 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
    }

    /**
    - * check_asym_packing - Check to see if the group is packed into the
    - * sched domain.
    - *
    - * This is primarily intended to used at the sibling level. Some
    - * cores like POWER7 prefer to use lower numbered SMT threads. In the
    - * case of POWER7, it can move to lower SMT modes only when higher
    - * threads are idle. When in lower SMT modes, the threads will
    - * perform better since they share less core resources. Hence when we
    - * have idle threads, we want them to be the higher ones.
    - *
    - * This packing function is run on idle threads. It checks to see if
    - * the busiest CPU in this domain (core in the P7 case) has a higher
    - * CPU number than the packing function is being run on. Here we are
    - * assuming lower CPU number will be equivalent to lower a SMT thread
    - * number.
    - *
    - * Return: 1 when packing is required and a task should be moved to
    - * this CPU. The amount of the imbalance is returned in env->imbalance.
    - *
    - * @env: The load balancing environment.
    - * @sds: Statistics of the sched_domain which is to be packed
    - */
    -static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
    -{
    - int busiest_cpu;
    -
    - if (!(env->sd->flags & SD_ASYM_PACKING))
    - return 0;
    -
    - if (env->idle == CPU_NOT_IDLE)
    - return 0;
    -
    - if (!sds->busiest)
    - return 0;
    -
    - busiest_cpu = sds->busiest->asym_prefer_cpu;
    - if (sched_asym_prefer(busiest_cpu, env->dst_cpu))
    - return 0;
    -
    - env->imbalance = sds->busiest_stat.group_load;
    -
    - return 1;
    -}
    -
    -/**
    * fix_small_imbalance - Calculate the minor imbalance that exists
    * amongst the groups of a sched_domain, during
    * load balancing.
    @@ -8401,6 +8365,11 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
    local = &sds->local_stat;
    busiest = &sds->busiest_stat;

    + if (busiest->group_asym_packing) {
    + env->imbalance = busiest->group_load;
    + return;
    + }
    +
    if (busiest->group_type == group_imbalanced) {
    /*
    * In the group_imb case we cannot rely on group-wide averages
    @@ -8505,8 +8474,8 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
    busiest = &sds.busiest_stat;

    /* ASYM feature bypasses nice load balance check */
    - if (check_asym_packing(env, &sds))
    - return sds.busiest;
    + if (busiest->group_asym_packing)
    + goto force_balance;

    /* There is no busy sibling group to pull tasks from */
    if (!sds.busiest || busiest->sum_nr_running == 0)
    --
    2.7.4
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