Merge branch 'sched/balancing' into sched/core

1 files changed, 515 insertions, 250 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 7b389c74f8ff..9f8506d68fdc 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3189,246 +3189,479 @@ static int move_one_task(struct rq *this_rq, int this_cpu, struct rq *busiest,
 
         return 0;
 }
+/********** Helpers for find_busiest_group ************************/
+/**
+ * sd_lb_stats - Structure to store the statistics of a sched_domain
+ *              during load balancing.
+ */
+struct sd_lb_stats {
+        struct sched_group *busiest; /* Busiest group in this sd */
+        struct sched_group *this;  /* Local group in this sd */
+        unsigned long total_load;  /* Total load of all groups in sd */
+        unsigned long total_pwr;   /*   Total power of all groups in sd */
+        unsigned long avg_load;    /* Average load across all groups in sd */
+
+        /** Statistics of this group */
+        unsigned long this_load;
+        unsigned long this_load_per_task;
+        unsigned long this_nr_running;
+
+        /* Statistics of the busiest group */
+        unsigned long max_load;
+        unsigned long busiest_load_per_task;
+        unsigned long busiest_nr_running;
+
+        int group_imb; /* Is there imbalance in this sd */
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+        int power_savings_balance; /* Is powersave balance needed for this sd */
+        struct sched_group *group_min; /* Least loaded group in sd */
+        struct sched_group *group_leader; /* Group which relieves group_min */
+        unsigned long min_load_per_task; /* load_per_task in group_min */
+        unsigned long leader_nr_running; /* Nr running of group_leader */
+        unsigned long min_nr_running; /* Nr running of group_min */
+#endif
+};
 
-/*
- * find_busiest_group finds and returns the busiest CPU group within the
- * domain. It calculates and returns the amount of weighted load which
- * should be moved to restore balance via the imbalance parameter.
+/**
+ * sg_lb_stats - stats of a sched_group required for load_balancing
+ */
+struct sg_lb_stats {
+        unsigned long avg_load; /*Avg load across the CPUs of the group */
+        unsigned long group_load; /* Total load over the CPUs of the group */
+        unsigned long sum_nr_running; /* Nr tasks running in the group */
+        unsigned long sum_weighted_load; /* Weighted load of group's tasks */
+        unsigned long group_capacity;
+        int group_imb; /* Is there an imbalance in the group ? */
+};
+
+/**
+ * group_first_cpu - Returns the first cpu in the cpumask of a sched_group.
+ * @group: The group whose first cpu is to be returned.
  */
-static struct sched_group *
-find_busiest_group(struct sched_domain *sd, int this_cpu,
-                   unsigned long *imbalance, enum cpu_idle_type idle,
-                   int *sd_idle, const struct cpumask *cpus, int *balance)
+static inline unsigned int group_first_cpu(struct sched_group *group)
 {
-        struct sched_group *busiest = NULL, *this = NULL, *group = sd->groups;
-        unsigned long max_load, avg_load, total_load, this_load, total_pwr;
-        unsigned long max_pull;
-        unsigned long busiest_load_per_task, busiest_nr_running;
-        unsigned long this_load_per_task, this_nr_running;
-        int load_idx, group_imb = 0;
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-        int power_savings_balance = 1;
-        unsigned long leader_nr_running = 0, min_load_per_task = 0;
-        unsigned long min_nr_running = ULONG_MAX;
-        struct sched_group *group_min = NULL, *group_leader = NULL;
-#endif
+        return cpumask_first(sched_group_cpus(group));
+}
 
-        max_load = this_load = total_load = total_pwr = 0;
-        busiest_load_per_task = busiest_nr_running = 0;
-        this_load_per_task = this_nr_running = 0;
+/**
+ * get_sd_load_idx - Obtain the load index for a given sched domain.
+ * @sd: The sched_domain whose load_idx is to be obtained.
+ * @idle: The Idle status of the CPU for whose sd load_icx is obtained.
+ */
+static inline int get_sd_load_idx(struct sched_domain *sd,
+                                        enum cpu_idle_type idle)
+{
+        int load_idx;
 
-        if (idle == CPU_NOT_IDLE)
+        switch (idle) {
+        case CPU_NOT_IDLE:
                 load_idx = sd->busy_idx;
-        else if (idle == CPU_NEWLY_IDLE)
+                break;
+
+        case CPU_NEWLY_IDLE:
                 load_idx = sd->newidle_idx;
-        else
+                break;
+        default:
                 load_idx = sd->idle_idx;
+                break;
+        }
 
-        do {
-                unsigned long load, group_capacity, max_cpu_load, min_cpu_load;
-                int local_group;
-                int i;
-                int __group_imb = 0;
-                unsigned int balance_cpu = -1, first_idle_cpu = 0;
-                unsigned long sum_nr_running, sum_weighted_load;
-                unsigned long sum_avg_load_per_task;
-                unsigned long avg_load_per_task;
+        return load_idx;
+}
 
-                local_group = cpumask_test_cpu(this_cpu,
-                                               sched_group_cpus(group));
 
-                if (local_group)
-                        balance_cpu = cpumask_first(sched_group_cpus(group));
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+/**
+ * init_sd_power_savings_stats - Initialize power savings statistics for
+ * the given sched_domain, during load balancing.
+ *
+ * @sd: Sched domain whose power-savings statistics are to be initialized.
+ * @sds: Variable containing the statistics for sd.
+ * @idle: Idle status of the CPU at which we're performing load-balancing.
+ */
+static inline void init_sd_power_savings_stats(struct sched_domain *sd,
+        struct sd_lb_stats *sds, enum cpu_idle_type idle)
+{
+        /*
+         * Busy processors will not participate in power savings
+         * balance.
+         */
+        if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+                sds->power_savings_balance = 0;
+        else {
+                sds->power_savings_balance = 1;
+                sds->min_nr_running = ULONG_MAX;
+                sds->leader_nr_running = 0;
+        }
+}
 
-                /* Tally up the load of all CPUs in the group */
-                sum_weighted_load = sum_nr_running = avg_load = 0;
-                sum_avg_load_per_task = avg_load_per_task = 0;
+/**
+ * update_sd_power_savings_stats - Update the power saving stats for a
+ * sched_domain while performing load balancing.
+ *
+ * @group: sched_group belonging to the sched_domain under consideration.
+ * @sds: Variable containing the statistics of the sched_domain
+ * @local_group: Does group contain the CPU for which we're performing
+ *              load balancing ?
+ * @sgs: Variable containing the statistics of the group.
+ */
+static inline void update_sd_power_savings_stats(struct sched_group *group,
+        struct sd_lb_stats *sds, int local_group, struct sg_lb_stats *sgs)
+{
 
-                max_cpu_load = 0;
-                min_cpu_load = ~0UL;
+        if (!sds->power_savings_balance)
+                return;
 
-                for_each_cpu_and(i, sched_group_cpus(group), cpus) {
-                        struct rq *rq = cpu_rq(i);
+        /*
+         * If the local group is idle or completely loaded
+         * no need to do power savings balance at this domain
+         */
+        if (local_group && (sds->this_nr_running >= sgs->group_capacity ||
+                                !sds->this_nr_running))
+                sds->power_savings_balance = 0;
 
-                        if (*sd_idle && rq->nr_running)
-                                *sd_idle = 0;
+        /*
+         * If a group is already running at full capacity or idle,
+         * don't include that group in power savings calculations
+         */
+        if (!sds->power_savings_balance ||
+                sgs->sum_nr_running >= sgs->group_capacity ||
+                !sgs->sum_nr_running)
+                return;
 
-                        /* Bias balancing toward cpus of our domain */
-                        if (local_group) {
-                                if (idle_cpu(i) && !first_idle_cpu) {
-                                        first_idle_cpu = 1;
-                                        balance_cpu = i;
-                                }
+        /*
+         * Calculate the group which has the least non-idle load.
+         * This is the group from where we need to pick up the load
+         * for saving power
+         */
+        if ((sgs->sum_nr_running < sds->min_nr_running) ||
+            (sgs->sum_nr_running == sds->min_nr_running &&
+             group_first_cpu(group) > group_first_cpu(sds->group_min))) {
+                sds->group_min = group;
+                sds->min_nr_running = sgs->sum_nr_running;
+                sds->min_load_per_task = sgs->sum_weighted_load /
+                                                sgs->sum_nr_running;
+        }
 
-                                load = target_load(i, load_idx);
-                        } else {
-                                load = source_load(i, load_idx);
-                                if (load > max_cpu_load)
-                                        max_cpu_load = load;
-                                if (min_cpu_load > load)
-                                        min_cpu_load = load;
-                        }
+        /*
+         * Calculate the group which is almost near its
+         * capacity but still has some space to pick up some load
+         * from other group and save more power
+         */
+        if (sgs->sum_nr_running > sgs->group_capacity - 1)
+                return;
 
-                        avg_load += load;
-                        sum_nr_running += rq->nr_running;
-                        sum_weighted_load += weighted_cpuload(i);
+        if (sgs->sum_nr_running > sds->leader_nr_running ||
+            (sgs->sum_nr_running == sds->leader_nr_running &&
+             group_first_cpu(group) < group_first_cpu(sds->group_leader))) {
+                sds->group_leader = group;
+                sds->leader_nr_running = sgs->sum_nr_running;
+        }
+}
 
-                        sum_avg_load_per_task += cpu_avg_load_per_task(i);
-                }
+/**
+ * check_power_save_busiest_group - Check if we have potential to perform
+ *      some power-savings balance. If yes, set the busiest group to be
+ *      the least loaded group in the sched_domain, so that it's CPUs can
+ *      be put to idle.
+ *
+ * @sds: Variable containing the statistics of the sched_domain
+ *      under consideration.
+ * @this_cpu: Cpu at which we're currently performing load-balancing.
+ * @imbalance: Variable to store the imbalance.
+ *
+ * Returns 1 if there is potential to perform power-savings balance.
+ * Else returns 0.
+ */
+static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
+                                        int this_cpu, unsigned long *imbalance)
+{
+        if (!sds->power_savings_balance)
+                return 0;
 
-                /*
-                 * First idle cpu or the first cpu(busiest) in this sched group
-                 * is eligible for doing load balancing at this and above
-                 * domains. In the newly idle case, we will allow all the cpu's
-                 * to do the newly idle load balance.
-                 */
-                if (idle != CPU_NEWLY_IDLE && local_group &&
-                    balance_cpu != this_cpu && balance) {
-                        *balance = 0;
-                        goto ret;
-                }
+        if (sds->this != sds->group_leader ||
+                        sds->group_leader == sds->group_min)
+                return 0;
 
-                total_load += avg_load;
-                total_pwr += group->__cpu_power;
+        *imbalance = sds->min_load_per_task;
+        sds->busiest = sds->group_min;
 
-                /* Adjust by relative CPU power of the group */
-                avg_load = sg_div_cpu_power(group,
-                                avg_load * SCHED_LOAD_SCALE);
+        if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
+                cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
+                        group_first_cpu(sds->group_leader);
+        }
 
+        return 1;
 
-                /*
-                 * Consider the group unbalanced when the imbalance is larger
-                 * than the average weight of two tasks.
-                 *
-                 * APZ: with cgroup the avg task weight can vary wildly and
-                 *      might not be a suitable number - should we keep a
-                 *      normalized nr_running number somewhere that negates
-                 *      the hierarchy?
-                 */
-                avg_load_per_task = sg_div_cpu_power(group,
-                                sum_avg_load_per_task * SCHED_LOAD_SCALE);
+}
+#else /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+static inline void init_sd_power_savings_stats(struct sched_domain *sd,
+        struct sd_lb_stats *sds, enum cpu_idle_type idle)
+{
+        return;
+}
+
+static inline void update_sd_power_savings_stats(struct sched_group *group,
+        struct sd_lb_stats *sds, int local_group, struct sg_lb_stats *sgs)
+{
+        return;
+}
+
+static inline int check_power_save_busiest_group(struct sd_lb_stats *sds,
+                                        int this_cpu, unsigned long *imbalance)
+{
+        return 0;
+}
+#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
+
+
+/**
+ * update_sg_lb_stats - Update sched_group's statistics for load balancing.
+ * @group: sched_group whose statistics are to be updated.
+ * @this_cpu: Cpu for which load balance is currently performed.
+ * @idle: Idle status of this_cpu
+ * @load_idx: Load index of sched_domain of this_cpu for load calc.
+ * @sd_idle: Idle status of the sched_domain containing group.
+ * @local_group: Does group contain this_cpu.
+ * @cpus: Set of cpus considered for load balancing.
+ * @balance: Should we balance.
+ * @sgs: variable to hold the statistics for this group.
+ */
+static inline void update_sg_lb_stats(struct sched_group *group, int this_cpu,
+                        enum cpu_idle_type idle, int load_idx, int *sd_idle,
+                        int local_group, const struct cpumask *cpus,
+                        int *balance, struct sg_lb_stats *sgs)
+{
+        unsigned long load, max_cpu_load, min_cpu_load;
+        int i;
+        unsigned int balance_cpu = -1, first_idle_cpu = 0;
+        unsigned long sum_avg_load_per_task;
+        unsigned long avg_load_per_task;
 
-                if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
-                        __group_imb = 1;
+        if (local_group)
+                balance_cpu = group_first_cpu(group);
 
-                group_capacity = group->__cpu_power / SCHED_LOAD_SCALE;
+        /* Tally up the load of all CPUs in the group */
+        sum_avg_load_per_task = avg_load_per_task = 0;
+        max_cpu_load = 0;
+        min_cpu_load = ~0UL;
 
+        for_each_cpu_and(i, sched_group_cpus(group), cpus) {
+                struct rq *rq = cpu_rq(i);
+
+                if (*sd_idle && rq->nr_running)
+                        *sd_idle = 0;
+
+                /* Bias balancing toward cpus of our domain */
                 if (local_group) {
-                        this_load = avg_load;
-                        this = group;
-                        this_nr_running = sum_nr_running;
-                        this_load_per_task = sum_weighted_load;
-                } else if (avg_load > max_load &&
-                           (sum_nr_running > group_capacity || __group_imb)) {
-                        max_load = avg_load;
-                        busiest = group;
-                        busiest_nr_running = sum_nr_running;
-                        busiest_load_per_task = sum_weighted_load;
-                        group_imb = __group_imb;
+                        if (idle_cpu(i) && !first_idle_cpu) {
+                                first_idle_cpu = 1;
+                                balance_cpu = i;
+                        }
+
+                        load = target_load(i, load_idx);
+                } else {
+                        load = source_load(i, load_idx);
+                        if (load > max_cpu_load)
+                                max_cpu_load = load;
+                        if (min_cpu_load > load)
+                                min_cpu_load = load;
                 }
 
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-                /*
-                 * Busy processors will not participate in power savings
-                 * balance.
-                 */
-                if (idle == CPU_NOT_IDLE ||
-                                !(sd->flags & SD_POWERSAVINGS_BALANCE))
-                        goto group_next;
+                sgs->group_load += load;
+                sgs->sum_nr_running += rq->nr_running;
+                sgs->sum_weighted_load += weighted_cpuload(i);
 
-                /*
-                 * If the local group is idle or completely loaded
-                 * no need to do power savings balance at this domain
-                 */
-                if (local_group && (this_nr_running >= group_capacity ||
-                                    !this_nr_running))
-                        power_savings_balance = 0;
+                sum_avg_load_per_task += cpu_avg_load_per_task(i);
+        }
 
-                /*
-                 * If a group is already running at full capacity or idle,
-                 * don't include that group in power savings calculations
-                 */
-                if (!power_savings_balance || sum_nr_running >= group_capacity
-                    || !sum_nr_running)
-                        goto group_next;
+        /*
+         * First idle cpu or the first cpu(busiest) in this sched group
+         * is eligible for doing load balancing at this and above
+         * domains. In the newly idle case, we will allow all the cpu's
+         * to do the newly idle load balance.
+         */
+        if (idle != CPU_NEWLY_IDLE && local_group &&
+            balance_cpu != this_cpu && balance) {
+                *balance = 0;
+                return;
+        }
 
-                /*
-                 * Calculate the group which has the least non-idle load.
-                 * This is the group from where we need to pick up the load
-                 * for saving power
-                 */
-                if ((sum_nr_running < min_nr_running) ||
-                    (sum_nr_running == min_nr_running &&
-                     cpumask_first(sched_group_cpus(group)) >
-                     cpumask_first(sched_group_cpus(group_min)))) {
-                        group_min = group;
-                        min_nr_running = sum_nr_running;
-                        min_load_per_task = sum_weighted_load /
-                                                sum_nr_running;
-                }
+        /* Adjust by relative CPU power of the group */
+        sgs->avg_load = sg_div_cpu_power(group,
+                        sgs->group_load * SCHED_LOAD_SCALE);
 
-                /*
-                 * Calculate the group which is almost near its
-                 * capacity but still has some space to pick up some load
-                 * from other group and save more power
-                 */
-                if (sum_nr_running <= group_capacity - 1) {
-                        if (sum_nr_running > leader_nr_running ||
-                            (sum_nr_running == leader_nr_running &&
-                             cpumask_first(sched_group_cpus(group)) <
-                             cpumask_first(sched_group_cpus(group_leader)))) {
-                                group_leader = group;
-                                leader_nr_running = sum_nr_running;
-                        }
+
+        /*
+         * Consider the group unbalanced when the imbalance is larger
+         * than the average weight of two tasks.
+         *
+         * APZ: with cgroup the avg task weight can vary wildly and
+         *      might not be a suitable number - should we keep a
+         *      normalized nr_running number somewhere that negates
+         *      the hierarchy?
+         */
+        avg_load_per_task = sg_div_cpu_power(group,
+                        sum_avg_load_per_task * SCHED_LOAD_SCALE);
+
+        if ((max_cpu_load - min_cpu_load) > 2*avg_load_per_task)
+                sgs->group_imb = 1;
+
+        sgs->group_capacity = group->__cpu_power / SCHED_LOAD_SCALE;
+
+}
+
+/**
+ * update_sd_lb_stats - Update sched_group's statistics for load balancing.
+ * @sd: sched_domain whose statistics are to be updated.
+ * @this_cpu: Cpu for which load balance is currently performed.
+ * @idle: Idle status of this_cpu
+ * @sd_idle: Idle status of the sched_domain containing group.
+ * @cpus: Set of cpus considered for load balancing.
+ * @balance: Should we balance.
+ * @sds: variable to hold the statistics for this sched_domain.
+ */
+static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
+                        enum cpu_idle_type idle, int *sd_idle,
+                        const struct cpumask *cpus, int *balance,
+                        struct sd_lb_stats *sds)
+{
+        struct sched_group *group = sd->groups;
+        struct sg_lb_stats sgs;
+        int load_idx;
+
+        init_sd_power_savings_stats(sd, sds, idle);
+        load_idx = get_sd_load_idx(sd, idle);
+
+        do {
+                int local_group;
+
+                local_group = cpumask_test_cpu(this_cpu,
+                                               sched_group_cpus(group));
+                memset(&sgs, 0, sizeof(sgs));
+                update_sg_lb_stats(group, this_cpu, idle, load_idx, sd_idle,
+                                local_group, cpus, balance, &sgs);
+
+                if (local_group && balance && !(*balance))
+                        return;
+
+                sds->total_load += sgs.group_load;
+                sds->total_pwr += group->__cpu_power;
+
+                if (local_group) {
+                        sds->this_load = sgs.avg_load;
+                        sds->this = group;
+                        sds->this_nr_running = sgs.sum_nr_running;
+                        sds->this_load_per_task = sgs.sum_weighted_load;
+                } else if (sgs.avg_load > sds->max_load &&
+                           (sgs.sum_nr_running > sgs.group_capacity ||
+                                sgs.group_imb)) {
+                        sds->max_load = sgs.avg_load;
+                        sds->busiest = group;
+                        sds->busiest_nr_running = sgs.sum_nr_running;
+                        sds->busiest_load_per_task = sgs.sum_weighted_load;
+                        sds->group_imb = sgs.group_imb;
                 }
-group_next:
-#endif
+
+                update_sd_power_savings_stats(group, sds, local_group, &sgs);
                 group = group->next;
         } while (group != sd->groups);
 
-        if (!busiest || this_load >= max_load || busiest_nr_running == 0)
-                goto out_balanced;
-
-        avg_load = (SCHED_LOAD_SCALE * total_load) / total_pwr;
+}
 
-        if (this_load >= avg_load ||
-                        100*max_load <= sd->imbalance_pct*this_load)
-                goto out_balanced;
+/**
+ * fix_small_imbalance - Calculate the minor imbalance that exists
+ *                      amongst the groups of a sched_domain, during
+ *                      load balancing.
+ * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
+ * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
+ * @imbalance: Variable to store the imbalance.
+ */
+static inline void fix_small_imbalance(struct sd_lb_stats *sds,
+                                int this_cpu, unsigned long *imbalance)
+{
+        unsigned long tmp, pwr_now = 0, pwr_move = 0;
+        unsigned int imbn = 2;
+
+        if (sds->this_nr_running) {
+                sds->this_load_per_task /= sds->this_nr_running;
+                if (sds->busiest_load_per_task >
+                                sds->this_load_per_task)
+                        imbn = 1;
+        } else
+                sds->this_load_per_task =
+                        cpu_avg_load_per_task(this_cpu);
 
-        busiest_load_per_task /= busiest_nr_running;
-        if (group_imb)
-                busiest_load_per_task = min(busiest_load_per_task, avg_load);
+        if (sds->max_load - sds->this_load + sds->busiest_load_per_task >=
+                        sds->busiest_load_per_task * imbn) {
+                *imbalance = sds->busiest_load_per_task;
+                return;
+        }
 
         /*
-         * We're trying to get all the cpus to the average_load, so we don't
-         * want to push ourselves above the average load, nor do we wish to
-         * reduce the max loaded cpu below the average load, as either of these
-         * actions would just result in more rebalancing later, and ping-pong
-         * tasks around. Thus we look for the minimum possible imbalance.
-         * Negative imbalances (*we* are more loaded than anyone else) will
-         * be counted as no imbalance for these purposes -- we can't fix that
-         * by pulling tasks to us. Be careful of negative numbers as they'll
-         * appear as very large values with unsigned longs.
+         * OK, we don't have enough imbalance to justify moving tasks,
+         * however we may be able to increase total CPU power used by
+         * moving them.
          */
-        if (max_load <= busiest_load_per_task)
-                goto out_balanced;
 
+        pwr_now += sds->busiest->__cpu_power *
+                        min(sds->busiest_load_per_task, sds->max_load);
+        pwr_now += sds->this->__cpu_power *
+                        min(sds->this_load_per_task, sds->this_load);
+        pwr_now /= SCHED_LOAD_SCALE;
+
+        /* Amount of load we'd subtract */
+        tmp = sg_div_cpu_power(sds->busiest,
+                        sds->busiest_load_per_task * SCHED_LOAD_SCALE);
+        if (sds->max_load > tmp)
+                pwr_move += sds->busiest->__cpu_power *
+                        min(sds->busiest_load_per_task, sds->max_load - tmp);
+
+        /* Amount of load we'd add */
+        if (sds->max_load * sds->busiest->__cpu_power <
+                sds->busiest_load_per_task * SCHED_LOAD_SCALE)
+                tmp = sg_div_cpu_power(sds->this,
+                        sds->max_load * sds->busiest->__cpu_power);
+        else
+                tmp = sg_div_cpu_power(sds->this,
+                        sds->busiest_load_per_task * SCHED_LOAD_SCALE);
+        pwr_move += sds->this->__cpu_power *
+                        min(sds->this_load_per_task, sds->this_load + tmp);
+        pwr_move /= SCHED_LOAD_SCALE;
+
+        /* Move if we gain throughput */
+        if (pwr_move > pwr_now)
+                *imbalance = sds->busiest_load_per_task;
+}
+
+/**
+ * calculate_imbalance - Calculate the amount of imbalance present within the
+ *                       groups of a given sched_domain during load balance.
+ * @sds: statistics of the sched_domain whose imbalance is to be calculated.
+ * @this_cpu: Cpu for which currently load balance is being performed.
+ * @imbalance: The variable to store the imbalance.
+ */
+static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu,
+                unsigned long *imbalance)
+{
+        unsigned long max_pull;
         /*
          * In the presence of smp nice balancing, certain scenarios can have
          * max load less than avg load(as we skip the groups at or below
          * its cpu_power, while calculating max_load..)
          */
-        if (max_load < avg_load) {
+        if (sds->max_load < sds->avg_load) {
                 *imbalance = 0;
-                goto small_imbalance;
+                return fix_small_imbalance(sds, this_cpu, imbalance);
         }
 
         /* Don't want to pull so many tasks that a group would go idle */
-        max_pull = min(max_load - avg_load, max_load - busiest_load_per_task);
+        max_pull = min(sds->max_load - sds->avg_load,
+                        sds->max_load - sds->busiest_load_per_task);
 
         /* How much load to actually move to equalise the imbalance */
-        *imbalance = min(max_pull * busiest->__cpu_power,
-                                (avg_load - this_load) * this->__cpu_power)
+        *imbalance = min(max_pull * sds->busiest->__cpu_power,
+                (sds->avg_load - sds->this_load) * sds->this->__cpu_power)
                         / SCHED_LOAD_SCALE;
 
         /*
@@ -3437,78 +3670,110 @@ group_next:
          * a think about bumping its value to force at least one task to be
          * moved
          */
-        if (*imbalance < busiest_load_per_task) {
-                unsigned long tmp, pwr_now, pwr_move;
-                unsigned int imbn;
-
-small_imbalance:
-                pwr_move = pwr_now = 0;
-                imbn = 2;
-                if (this_nr_running) {
-                        this_load_per_task /= this_nr_running;
-                        if (busiest_load_per_task > this_load_per_task)
-                                imbn = 1;
-                } else
-                        this_load_per_task = cpu_avg_load_per_task(this_cpu);
+        if (*imbalance < sds->busiest_load_per_task)
+                return fix_small_imbalance(sds, this_cpu, imbalance);
 
-                if (max_load - this_load + busiest_load_per_task >=
-                                        busiest_load_per_task * imbn) {
-                        *imbalance = busiest_load_per_task;
-                        return busiest;
-                }
+}
+/******* find_busiest_group() helpers end here *********************/
 
-                /*
-                 * OK, we don't have enough imbalance to justify moving tasks,
-                 * however we may be able to increase total CPU power used by
-                 * moving them.
-                 */
+/**
+ * find_busiest_group - Returns the busiest group within the sched_domain
+ * if there is an imbalance. If there isn't an imbalance, and
+ * the user has opted for power-savings, it returns a group whose
+ * CPUs can be put to idle by rebalancing those tasks elsewhere, if
+ * such a group exists.
+ *
+ * Also calculates the amount of weighted load which should be moved
+ * to restore balance.
+ *
+ * @sd: The sched_domain whose busiest group is to be returned.
+ * @this_cpu: The cpu for which load balancing is currently being performed.
+ * @imbalance: Variable which stores amount of weighted load which should
+ *              be moved to restore balance/put a group to idle.
+ * @idle: The idle status of this_cpu.
+ * @sd_idle: The idleness of sd
+ * @cpus: The set of CPUs under consideration for load-balancing.
+ * @balance: Pointer to a variable indicating if this_cpu
+ *      is the appropriate cpu to perform load balancing at this_level.
+ *
+ * Returns:     - the busiest group if imbalance exists.
+ *              - If no imbalance and user has opted for power-savings balance,
+ *                 return the least loaded group whose CPUs can be
+ *                 put to idle by rebalancing its tasks onto our group.
+ */
+static struct sched_group *
+find_busiest_group(struct sched_domain *sd, int this_cpu,
+                   unsigned long *imbalance, enum cpu_idle_type idle,
+                   int *sd_idle, const struct cpumask *cpus, int *balance)
+{
+        struct sd_lb_stats sds;
 
-                pwr_now += busiest->__cpu_power *
-                                min(busiest_load_per_task, max_load);
-                pwr_now += this->__cpu_power *
-                                min(this_load_per_task, this_load);
-                pwr_now /= SCHED_LOAD_SCALE;
-
-                /* Amount of load we'd subtract */
-                tmp = sg_div_cpu_power(busiest,
-                                busiest_load_per_task * SCHED_LOAD_SCALE);
-                if (max_load > tmp)
-                        pwr_move += busiest->__cpu_power *
-                                min(busiest_load_per_task, max_load - tmp);
-
-                /* Amount of load we'd add */
-                if (max_load * busiest->__cpu_power <
-                                busiest_load_per_task * SCHED_LOAD_SCALE)
-                        tmp = sg_div_cpu_power(this,
-                                        max_load * busiest->__cpu_power);
-                else
-                        tmp = sg_div_cpu_power(this,
-                                busiest_load_per_task * SCHED_LOAD_SCALE);
-                pwr_move += this->__cpu_power *
-                                min(this_load_per_task, this_load + tmp);
-                pwr_move /= SCHED_LOAD_SCALE;
+        memset(&sds, 0, sizeof(sds));
 
-                /* Move if we gain throughput */
-                if (pwr_move > pwr_now)
-                        *imbalance = busiest_load_per_task;
-        }
+        /*
+         * Compute the various statistics relavent for load balancing at
+         * this level.
+         */
+        update_sd_lb_stats(sd, this_cpu, idle, sd_idle, cpus,
+                                        balance, &sds);
+
+        /* Cases where imbalance does not exist from POV of this_cpu */
+        /* 1) this_cpu is not the appropriate cpu to perform load balancing
+         *    at this level.
+         * 2) There is no busy sibling group to pull from.
+         * 3) This group is the busiest group.
+         * 4) This group is more busy than the avg busieness at this
+         *    sched_domain.
+         * 5) The imbalance is within the specified limit.
+         * 6) Any rebalance would lead to ping-pong
+         */
+        if (balance && !(*balance))
+                goto ret;
 
-        return busiest;
+        if (!sds.busiest || sds.busiest_nr_running == 0)
+                goto out_balanced;
 
-out_balanced:
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-        if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
-                goto ret;
+        if (sds.this_load >= sds.max_load)
+                goto out_balanced;
 
-        if (this == group_leader && group_leader != group_min) {
-                *imbalance = min_load_per_task;
-                if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP) {
-                        cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu =
-                                cpumask_first(sched_group_cpus(group_leader));
-                }
-                return group_min;
-        }
-#endif
+        sds.avg_load = (SCHED_LOAD_SCALE * sds.total_load) / sds.total_pwr;
+
+        if (sds.this_load >= sds.avg_load)
+                goto out_balanced;
+
+        if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load)
+                goto out_balanced;
+
+        sds.busiest_load_per_task /= sds.busiest_nr_running;
+        if (sds.group_imb)
+                sds.busiest_load_per_task =
+                        min(sds.busiest_load_per_task, sds.avg_load);
+
+        /*
+         * We're trying to get all the cpus to the average_load, so we don't
+         * want to push ourselves above the average load, nor do we wish to
+         * reduce the max loaded cpu below the average load, as either of these
+         * actions would just result in more rebalancing later, and ping-pong
+         * tasks around. Thus we look for the minimum possible imbalance.
+         * Negative imbalances (*we* are more loaded than anyone else) will
+         * be counted as no imbalance for these purposes -- we can't fix that
+         * by pulling tasks to us. Be careful of negative numbers as they'll
+         * appear as very large values with unsigned longs.
+         */
+        if (sds.max_load <= sds.busiest_load_per_task)
+                goto out_balanced;
+
+        /* Looks like there is an imbalance. Compute it */
+        calculate_imbalance(&sds, this_cpu, imbalance);
+        return sds.busiest;
+
+out_balanced:
+        /*
+         * There is no obvious imbalance. But check if we can do some balancing
+         * to save power.
+         */
+        if (check_power_save_busiest_group(&sds, this_cpu, imbalance))
+                return sds.busiest;
 ret:
         *imbalance = 0;
         return NULL;