1 files changed, 371 insertions, 161 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index a878b5332daa..806d1b227a21 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2287,13 +2287,6 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
 	unsigned long power = SCHED_LOAD_SCALE;
 	struct sched_group *sdg = sd->groups;
 
-	if (sched_feat(ARCH_POWER))
-		power *= arch_scale_freq_power(sd, cpu);
-	else
-		power *= default_scale_freq_power(sd, cpu);
-
-	power >>= SCHED_LOAD_SHIFT;
-
 	if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
 		if (sched_feat(ARCH_POWER))
 			power *= arch_scale_smt_power(sd, cpu);
@@ -2303,6 +2296,15 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
 		power >>= SCHED_LOAD_SHIFT;
 	}
 
+	sdg->cpu_power_orig = power;
+
+	if (sched_feat(ARCH_POWER))
+		power *= arch_scale_freq_power(sd, cpu);
+	else
+		power *= default_scale_freq_power(sd, cpu);
+
+	power >>= SCHED_LOAD_SHIFT;
+
 	power *= scale_rt_power(cpu);
 	power >>= SCHED_LOAD_SHIFT;
 
@@ -2335,6 +2337,31 @@ static void update_group_power(struct sched_domain *sd, int cpu)
 	sdg->cpu_power = power;
 }
 
+/*
+ * Try and fix up capacity for tiny siblings, this is needed when
+ * things like SD_ASYM_PACKING need f_b_g to select another sibling
+ * which on its own isn't powerful enough.
+ *
+ * See update_sd_pick_busiest() and check_asym_packing().
+ */
+static inline int
+fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
+{
+	/*
+	 * Only siblings can have significantly less than SCHED_LOAD_SCALE
+	 */
+	if (sd->level != SD_LV_SIBLING)
+		return 0;
+
+	/*
+	 * If ~90% of the cpu_power is still there, we're good.
+	 */
+	if (group->cpu_power * 32 > group->cpu_power_orig * 29)
+		return 1;
+
+	return 0;
+}
+
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @sd: The sched_domain whose statistics are to be updated.
@@ -2400,14 +2427,14 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 	 * 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 = 0;
-		return;
+	if (idle != CPU_NEWLY_IDLE && local_group) {
+		if (balance_cpu != this_cpu) {
+			*balance = 0;
+			return;
+		}
+		update_group_power(sd, this_cpu);
 	}
 
-	update_group_power(sd, this_cpu);
-
 	/* Adjust by relative CPU power of the group */
 	sgs->avg_load = (sgs->group_load * SCHED_LOAD_SCALE) / group->cpu_power;
 
@@ -2428,6 +2455,51 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 
 	sgs->group_capacity =
 		DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
+	if (!sgs->group_capacity)
+		sgs->group_capacity = fix_small_capacity(sd, group);
+}
+
+/**
+ * update_sd_pick_busiest - return 1 on busiest group
+ * @sd: sched_domain whose statistics are to be checked
+ * @sds: sched_domain statistics
+ * @sg: sched_group candidate to be checked for being the busiest
+ * @sgs: sched_group statistics
+ * @this_cpu: the current cpu
+ *
+ * Determine if @sg is a busier group than the previously selected
+ * busiest group.
+ */
+static bool update_sd_pick_busiest(struct sched_domain *sd,
+				   struct sd_lb_stats *sds,
+				   struct sched_group *sg,
+				   struct sg_lb_stats *sgs,
+				   int this_cpu)
+{
+	if (sgs->avg_load <= sds->max_load)
+		return false;
+
+	if (sgs->sum_nr_running > sgs->group_capacity)
+		return true;
+
+	if (sgs->group_imb)
+		return true;
+
+	/*
+	 * ASYM_PACKING needs to move all the work to the lowest
+	 * numbered CPUs in the group, therefore mark all groups
+	 * higher than ourself as busy.
+	 */
+	if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running &&
+	    this_cpu < group_first_cpu(sg)) {
+		if (!sds->busiest)
+			return true;
+
+		if (group_first_cpu(sds->busiest) > group_first_cpu(sg))
+			return true;
+	}
+
+	return false;
 }
 
 /**
@@ -2435,7 +2507,7 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
  * @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.
+ * @sd_idle: Idle status of the sched_domain containing sg.
  * @cpus: Set of cpus considered for load balancing.
  * @balance: Should we balance.
  * @sds: variable to hold the statistics for this sched_domain.
@@ -2446,7 +2518,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 			struct sd_lb_stats *sds)
 {
 	struct sched_domain *child = sd->child;
-	struct sched_group *group = sd->groups;
+	struct sched_group *sg = sd->groups;
 	struct sg_lb_stats sgs;
 	int load_idx, prefer_sibling = 0;
 
@@ -2459,21 +2531,20 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 	do {
 		int local_group;
 
-		local_group = cpumask_test_cpu(this_cpu,
-					       sched_group_cpus(group));
+		local_group = cpumask_test_cpu(this_cpu, sched_group_cpus(sg));
 		memset(&sgs, 0, sizeof(sgs));
-		update_sg_lb_stats(sd, group, this_cpu, idle, load_idx, sd_idle,
+		update_sg_lb_stats(sd, sg, this_cpu, idle, load_idx, sd_idle,
 				local_group, cpus, balance, &sgs);
 
 		if (local_group && !(*balance))
 			return;
 
 		sds->total_load += sgs.group_load;
-		sds->total_pwr += group->cpu_power;
+		sds->total_pwr += sg->cpu_power;
 
 		/*
 		 * In case the child domain prefers tasks go to siblings
-		 * first, lower the group capacity to one so that we'll try
+		 * first, lower the sg capacity to one so that we'll try
 		 * and move all the excess tasks away.
 		 */
 		if (prefer_sibling)
@@ -2481,23 +2552,72 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 
 		if (local_group) {
 			sds->this_load = sgs.avg_load;
-			sds->this = group;
+			sds->this = sg;
 			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)) {
+		} else if (update_sd_pick_busiest(sd, sds, sg, &sgs, this_cpu)) {
 			sds->max_load = sgs.avg_load;
-			sds->busiest = group;
+			sds->busiest = sg;
 			sds->busiest_nr_running = sgs.sum_nr_running;
 			sds->busiest_group_capacity = sgs.group_capacity;
 			sds->busiest_load_per_task = sgs.sum_weighted_load;
 			sds->group_imb = sgs.group_imb;
 		}
 
-		update_sd_power_savings_stats(group, sds, local_group, &sgs);
-		group = group->next;
-	} while (group != sd->groups);
+		update_sd_power_savings_stats(sg, sds, local_group, &sgs);
+		sg = sg->next;
+	} while (sg != sd->groups);
+}
+
+int __weak arch_sd_sibling_asym_packing(void)
+{
+       return 0*SD_ASYM_PACKING;
+}
+
+/**
+ * check_asym_packing - Check to see if the group is packed into the
+ *			sched doman.
+ *
+ * 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.
+ *
+ * Returns 1 when packing is required and a task should be moved to
+ * this CPU.  The amount of the imbalance is returned in *imbalance.
+ *
+ * @sd: The sched_domain whose packing is to be checked.
+ * @sds: Statistics of the sched_domain which is to be packed
+ * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
+ * @imbalance: returns amount of imbalanced due to packing.
+ */
+static int check_asym_packing(struct sched_domain *sd,
+			      struct sd_lb_stats *sds,
+			      int this_cpu, unsigned long *imbalance)
+{
+	int busiest_cpu;
+
+	if (!(sd->flags & SD_ASYM_PACKING))
+		return 0;
+
+	if (!sds->busiest)
+		return 0;
+
+	busiest_cpu = group_first_cpu(sds->busiest);
+	if (this_cpu > busiest_cpu)
+		return 0;
+
+	*imbalance = DIV_ROUND_CLOSEST(sds->max_load * sds->busiest->cpu_power,
+				       SCHED_LOAD_SCALE);
+	return 1;
 }
 
 /**
@@ -2692,6 +2812,10 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 	if (!(*balance))
 		goto ret;
 
+	if ((idle == CPU_IDLE || idle == CPU_NEWLY_IDLE) &&
+	    check_asym_packing(sd, &sds, this_cpu, imbalance))
+		return sds.busiest;
+
 	if (!sds.busiest || sds.busiest_nr_running == 0)
 		goto out_balanced;
 
@@ -2726,8 +2850,9 @@ ret:
  * find_busiest_queue - find the busiest runqueue among the cpus in group.
  */
 static struct rq *
-find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
-		   unsigned long imbalance, const struct cpumask *cpus)
+find_busiest_queue(struct sched_domain *sd, struct sched_group *group,
+		   enum cpu_idle_type idle, unsigned long imbalance,
+		   const struct cpumask *cpus)
 {
 	struct rq *busiest = NULL, *rq;
 	unsigned long max_load = 0;
@@ -2738,6 +2863,9 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
 		unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
 		unsigned long wl;
 
+		if (!capacity)
+			capacity = fix_small_capacity(sd, group);
+
 		if (!cpumask_test_cpu(i, cpus))
 			continue;
 
@@ -2777,9 +2905,19 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
 /* Working cpumask for load_balance and load_balance_newidle. */
 static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);
 
-static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle)
+static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle,
+			       int busiest_cpu, int this_cpu)
 {
 	if (idle == CPU_NEWLY_IDLE) {
+
+		/*
+		 * ASYM_PACKING needs to force migrate tasks from busy but
+		 * higher numbered CPUs in order to pack all tasks in the
+		 * lowest numbered CPUs.
+		 */
+		if ((sd->flags & SD_ASYM_PACKING) && busiest_cpu > this_cpu)
+			return 1;
+
 		/*
 		 * The only task running in a non-idle cpu can be moved to this
 		 * cpu in an attempt to completely freeup the other CPU
@@ -2854,7 +2992,7 @@ redo:
 		goto out_balanced;
 	}
 
-	busiest = find_busiest_queue(group, idle, imbalance, cpus);
+	busiest = find_busiest_queue(sd, group, idle, imbalance, cpus);
 	if (!busiest) {
 		schedstat_inc(sd, lb_nobusyq[idle]);
 		goto out_balanced;
@@ -2898,7 +3036,8 @@ redo:
 		schedstat_inc(sd, lb_failed[idle]);
 		sd->nr_balance_failed++;
 
-		if (need_active_balance(sd, sd_idle, idle)) {
+		if (need_active_balance(sd, sd_idle, idle, cpu_of(busiest),
+					this_cpu)) {
 			raw_spin_lock_irqsave(&busiest->lock, flags);
 
 			/* don't kick the active_load_balance_cpu_stop,
@@ -3093,13 +3232,40 @@ out_unlock:
 }
 
 #ifdef CONFIG_NO_HZ
+
+static DEFINE_PER_CPU(struct call_single_data, remote_sched_softirq_cb);
+
+static void trigger_sched_softirq(void *data)
+{
+	raise_softirq_irqoff(SCHED_SOFTIRQ);
+}
+
+static inline void init_sched_softirq_csd(struct call_single_data *csd)
+{
+	csd->func = trigger_sched_softirq;
+	csd->info = NULL;
+	csd->flags = 0;
+	csd->priv = 0;
+}
+
+/*
+ * idle load balancing details
+ * - One of the idle CPUs nominates itself as idle load_balancer, while
+ *   entering idle.
+ * - This idle load balancer CPU will also go into tickless mode when
+ *   it is idle, just like all other idle CPUs
+ * - When one of the busy CPUs notice that there may be an idle rebalancing
+ *   needed, they will kick the idle load balancer, which then does idle
+ *   load balancing for all the idle CPUs.
+ */
 static struct {
 	atomic_t load_balancer;
-	cpumask_var_t cpu_mask;
-	cpumask_var_t ilb_grp_nohz_mask;
-} nohz ____cacheline_aligned = {
-	.load_balancer = ATOMIC_INIT(-1),
-};
+	atomic_t first_pick_cpu;
+	atomic_t second_pick_cpu;
+	cpumask_var_t idle_cpus_mask;
+	cpumask_var_t grp_idle_mask;
+	unsigned long next_balance;     /* in jiffy units */
+} nohz ____cacheline_aligned;
 
 int get_nohz_load_balancer(void)
 {
@@ -3153,17 +3319,17 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
  */
 static inline int is_semi_idle_group(struct sched_group *ilb_group)
 {
-	cpumask_and(nohz.ilb_grp_nohz_mask, nohz.cpu_mask,
+	cpumask_and(nohz.grp_idle_mask, nohz.idle_cpus_mask,
 					sched_group_cpus(ilb_group));
 
 	/*
 	 * A sched_group is semi-idle when it has atleast one busy cpu
 	 * and atleast one idle cpu.
 	 */
-	if (cpumask_empty(nohz.ilb_grp_nohz_mask))
+	if (cpumask_empty(nohz.grp_idle_mask))
 		return 0;
 
-	if (cpumask_equal(nohz.ilb_grp_nohz_mask, sched_group_cpus(ilb_group)))
+	if (cpumask_equal(nohz.grp_idle_mask, sched_group_cpus(ilb_group)))
 		return 0;
 
 	return 1;
@@ -3196,7 +3362,7 @@ static int find_new_ilb(int cpu)
 	 * Optimize for the case when we have no idle CPUs or only one
 	 * idle CPU. Don't walk the sched_domain hierarchy in such cases
 	 */
-	if (cpumask_weight(nohz.cpu_mask) < 2)
+	if (cpumask_weight(nohz.idle_cpus_mask) < 2)
 		goto out_done;
 
 	for_each_flag_domain(cpu, sd, SD_POWERSAVINGS_BALANCE) {
@@ -3204,7 +3370,7 @@ static int find_new_ilb(int cpu)
 
 		do {
 			if (is_semi_idle_group(ilb_group))
-				return cpumask_first(nohz.ilb_grp_nohz_mask);
+				return cpumask_first(nohz.grp_idle_mask);
 
 			ilb_group = ilb_group->next;
 
@@ -3212,98 +3378,116 @@ static int find_new_ilb(int cpu)
 	}
 
 out_done:
-	return cpumask_first(nohz.cpu_mask);
+	return nr_cpu_ids;
 }
 #else /*  (CONFIG_SCHED_MC || CONFIG_SCHED_SMT) */
 static inline int find_new_ilb(int call_cpu)
 {
-	return cpumask_first(nohz.cpu_mask);
+	return nr_cpu_ids;
 }
 #endif
 
 /*
+ * Kick a CPU to do the nohz balancing, if it is time for it. We pick the
+ * nohz_load_balancer CPU (if there is one) otherwise fallback to any idle
+ * CPU (if there is one).
+ */
+static void nohz_balancer_kick(int cpu)
+{
+	int ilb_cpu;
+
+	nohz.next_balance++;
+
+	ilb_cpu = get_nohz_load_balancer();
+
+	if (ilb_cpu >= nr_cpu_ids) {
+		ilb_cpu = cpumask_first(nohz.idle_cpus_mask);
+		if (ilb_cpu >= nr_cpu_ids)
+			return;
+	}
+
+	if (!cpu_rq(ilb_cpu)->nohz_balance_kick) {
+		struct call_single_data *cp;
+
+		cpu_rq(ilb_cpu)->nohz_balance_kick = 1;
+		cp = &per_cpu(remote_sched_softirq_cb, cpu);
+		__smp_call_function_single(ilb_cpu, cp, 0);
+	}
+	return;
+}
+
+/*
  * This routine will try to nominate the ilb (idle load balancing)
  * owner among the cpus whose ticks are stopped. ilb owner will do the idle
- * load balancing on behalf of all those cpus. If all the cpus in the system
- * go into this tickless mode, then there will be no ilb owner (as there is
- * no need for one) and all the cpus will sleep till the next wakeup event
- * arrives...
- *
- * For the ilb owner, tick is not stopped. And this tick will be used
- * for idle load balancing. ilb owner will still be part of
- * nohz.cpu_mask..
+ * load balancing on behalf of all those cpus.
  *
- * While stopping the tick, this cpu will become the ilb owner if there
- * is no other owner. And will be the owner till that cpu becomes busy
- * or if all cpus in the system stop their ticks at which point
- * there is no need for ilb owner.
+ * When the ilb owner becomes busy, we will not have new ilb owner until some
+ * idle CPU wakes up and goes back to idle or some busy CPU tries to kick
+ * idle load balancing by kicking one of the idle CPUs.
  *
- * When the ilb owner becomes busy, it nominates another owner, during the
- * next busy scheduler_tick()
+ * Ticks are stopped for the ilb owner as well, with busy CPU kicking this
+ * ilb owner CPU in future (when there is a need for idle load balancing on
+ * behalf of all idle CPUs).
  */
-int select_nohz_load_balancer(int stop_tick)
+void select_nohz_load_balancer(int stop_tick)
 {
 	int cpu = smp_processor_id();
 
 	if (stop_tick) {
-		cpu_rq(cpu)->in_nohz_recently = 1;
-
 		if (!cpu_active(cpu)) {
 			if (atomic_read(&nohz.load_balancer) != cpu)
-				return 0;
+				return;
 
 			/*
 			 * If we are going offline and still the leader,
 			 * give up!
 			 */
-			if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
+			if (atomic_cmpxchg(&nohz.load_balancer, cpu,
+					   nr_cpu_ids) != cpu)
 				BUG();
 
-			return 0;
+			return;
 		}
 
-		cpumask_set_cpu(cpu, nohz.cpu_mask);
+		cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
 
-		/* time for ilb owner also to sleep */
-		if (cpumask_weight(nohz.cpu_mask) == num_active_cpus()) {
-			if (atomic_read(&nohz.load_balancer) == cpu)
-				atomic_set(&nohz.load_balancer, -1);
-			return 0;
-		}
+		if (atomic_read(&nohz.first_pick_cpu) == cpu)
+			atomic_cmpxchg(&nohz.first_pick_cpu, cpu, nr_cpu_ids);
+		if (atomic_read(&nohz.second_pick_cpu) == cpu)
+			atomic_cmpxchg(&nohz.second_pick_cpu, cpu, nr_cpu_ids);
 
-		if (atomic_read(&nohz.load_balancer) == -1) {
-			/* make me the ilb owner */
-			if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) == -1)
-				return 1;
-		} else if (atomic_read(&nohz.load_balancer) == cpu) {
+		if (atomic_read(&nohz.load_balancer) >= nr_cpu_ids) {
 			int new_ilb;
 
-			if (!(sched_smt_power_savings ||
-						sched_mc_power_savings))
-				return 1;
+			/* make me the ilb owner */
+			if (atomic_cmpxchg(&nohz.load_balancer, nr_cpu_ids,
+					   cpu) != nr_cpu_ids)
+				return;
+
 			/*
 			 * Check to see if there is a more power-efficient
 			 * ilb.
 			 */
 			new_ilb = find_new_ilb(cpu);
 			if (new_ilb < nr_cpu_ids && new_ilb != cpu) {
-				atomic_set(&nohz.load_balancer, -1);
+				atomic_set(&nohz.load_balancer, nr_cpu_ids);
 				resched_cpu(new_ilb);
-				return 0;
+				return;
 			}
-			return 1;
+			return;
 		}
 	} else {
-		if (!cpumask_test_cpu(cpu, nohz.cpu_mask))
-			return 0;
+		if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
+			return;
 
-		cpumask_clear_cpu(cpu, nohz.cpu_mask);
+		cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
 
 		if (atomic_read(&nohz.load_balancer) == cpu)
-			if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
+			if (atomic_cmpxchg(&nohz.load_balancer, cpu,
+					   nr_cpu_ids) != cpu)
 				BUG();
 	}
-	return 0;
+	return;
 }
 #endif
 
@@ -3385,11 +3569,102 @@ out:
 		rq->next_balance = next_balance;
 }
 
+#ifdef CONFIG_NO_HZ
 /*
- * run_rebalance_domains is triggered when needed from the scheduler tick.
- * In CONFIG_NO_HZ case, the idle load balance owner will do the
+ * In CONFIG_NO_HZ case, the idle balance kickee will do the
  * rebalancing for all the cpus for whom scheduler ticks are stopped.
  */
+static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
+{
+	struct rq *this_rq = cpu_rq(this_cpu);
+	struct rq *rq;
+	int balance_cpu;
+
+	if (idle != CPU_IDLE || !this_rq->nohz_balance_kick)
+		return;
+
+	for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
+		if (balance_cpu == this_cpu)
+			continue;
+
+		/*
+		 * If this cpu gets work to do, stop the load balancing
+		 * work being done for other cpus. Next load
+		 * balancing owner will pick it up.
+		 */
+		if (need_resched()) {
+			this_rq->nohz_balance_kick = 0;
+			break;
+		}
+
+		raw_spin_lock_irq(&this_rq->lock);
+		update_rq_clock(this_rq);
+		update_cpu_load(this_rq);
+		raw_spin_unlock_irq(&this_rq->lock);
+
+		rebalance_domains(balance_cpu, CPU_IDLE);
+
+		rq = cpu_rq(balance_cpu);
+		if (time_after(this_rq->next_balance, rq->next_balance))
+			this_rq->next_balance = rq->next_balance;
+	}
+	nohz.next_balance = this_rq->next_balance;
+	this_rq->nohz_balance_kick = 0;
+}
+
+/*
+ * Current heuristic for kicking the idle load balancer
+ * - first_pick_cpu is the one of the busy CPUs. It will kick
+ *   idle load balancer when it has more than one process active. This
+ *   eliminates the need for idle load balancing altogether when we have
+ *   only one running process in the system (common case).
+ * - If there are more than one busy CPU, idle load balancer may have
+ *   to run for active_load_balance to happen (i.e., two busy CPUs are
+ *   SMT or core siblings and can run better if they move to different
+ *   physical CPUs). So, second_pick_cpu is the second of the busy CPUs
+ *   which will kick idle load balancer as soon as it has any load.
+ */
+static inline int nohz_kick_needed(struct rq *rq, int cpu)
+{
+	unsigned long now = jiffies;
+	int ret;
+	int first_pick_cpu, second_pick_cpu;
+
+	if (time_before(now, nohz.next_balance))
+		return 0;
+
+	if (!rq->nr_running)
+		return 0;
+
+	first_pick_cpu = atomic_read(&nohz.first_pick_cpu);
+	second_pick_cpu = atomic_read(&nohz.second_pick_cpu);
+
+	if (first_pick_cpu < nr_cpu_ids && first_pick_cpu != cpu &&
+	    second_pick_cpu < nr_cpu_ids && second_pick_cpu != cpu)
+		return 0;
+
+	ret = atomic_cmpxchg(&nohz.first_pick_cpu, nr_cpu_ids, cpu);
+	if (ret == nr_cpu_ids || ret == cpu) {
+		atomic_cmpxchg(&nohz.second_pick_cpu, cpu, nr_cpu_ids);
+		if (rq->nr_running > 1)
+			return 1;
+	} else {
+		ret = atomic_cmpxchg(&nohz.second_pick_cpu, nr_cpu_ids, cpu);
+		if (ret == nr_cpu_ids || ret == cpu) {
+			if (rq->nr_running)
+				return 1;
+		}
+	}
+	return 0;
+}
+#else
+static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle) { }
+#endif
+
+/*
+ * run_rebalance_domains is triggered when needed from the scheduler tick.
+ * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
+ */
 static void run_rebalance_domains(struct softirq_action *h)
 {
 	int this_cpu = smp_processor_id();
@@ -3399,37 +3674,12 @@ static void run_rebalance_domains(struct softirq_action *h)
 
 	rebalance_domains(this_cpu, idle);
 
-#ifdef CONFIG_NO_HZ
 	/*
-	 * If this cpu is the owner for idle load balancing, then do the
+	 * If this cpu has a pending nohz_balance_kick, then do the
 	 * balancing on behalf of the other idle cpus whose ticks are
 	 * stopped.
 	 */
-	if (this_rq->idle_at_tick &&
-	    atomic_read(&nohz.load_balancer) == this_cpu) {
-		struct rq *rq;
-		int balance_cpu;
-
-		for_each_cpu(balance_cpu, nohz.cpu_mask) {
-			if (balance_cpu == this_cpu)
-				continue;
-
-			/*
-			 * If this cpu gets work to do, stop the load balancing
-			 * work being done for other cpus. Next load
-			 * balancing owner will pick it up.
-			 */
-			if (need_resched())
-				break;
-
-			rebalance_domains(balance_cpu, CPU_IDLE);
-
-			rq = cpu_rq(balance_cpu);
-			if (time_after(this_rq->next_balance, rq->next_balance))
-				this_rq->next_balance = rq->next_balance;
-		}
-	}
-#endif
+	nohz_idle_balance(this_cpu, idle);
 }
 
 static inline int on_null_domain(int cpu)
@@ -3439,57 +3689,17 @@ static inline int on_null_domain(int cpu)
 
 /*
  * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
- *
- * In case of CONFIG_NO_HZ, this is the place where we nominate a new
- * idle load balancing owner or decide to stop the periodic load balancing,
- * if the whole system is idle.
  */
 static inline void trigger_load_balance(struct rq *rq, int cpu)
 {
-#ifdef CONFIG_NO_HZ
-	/*
-	 * If we were in the nohz mode recently and busy at the current
-	 * scheduler tick, then check if we need to nominate new idle
-	 * load balancer.
-	 */
-	if (rq->in_nohz_recently && !rq->idle_at_tick) {
-		rq->in_nohz_recently = 0;
-
-		if (atomic_read(&nohz.load_balancer) == cpu) {
-			cpumask_clear_cpu(cpu, nohz.cpu_mask);
-			atomic_set(&nohz.load_balancer, -1);
-		}
-
-		if (atomic_read(&nohz.load_balancer) == -1) {
-			int ilb = find_new_ilb(cpu);
-
-			if (ilb < nr_cpu_ids)
-				resched_cpu(ilb);
-		}
-	}
-
-	/*
-	 * If this cpu is idle and doing idle load balancing for all the
-	 * cpus with ticks stopped, is it time for that to stop?
-	 */
-	if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) == cpu &&
-	    cpumask_weight(nohz.cpu_mask) == num_online_cpus()) {
-		resched_cpu(cpu);
-		return;
-	}
-
-	/*
-	 * If this cpu is idle and the idle load balancing is done by
-	 * someone else, then no need raise the SCHED_SOFTIRQ
-	 */
-	if (rq->idle_at_tick && atomic_read(&nohz.load_balancer) != cpu &&
-	    cpumask_test_cpu(cpu, nohz.cpu_mask))
-		return;
-#endif
 	/* Don't need to rebalance while attached to NULL domain */
 	if (time_after_eq(jiffies, rq->next_balance) &&
 	    likely(!on_null_domain(cpu)))
 		raise_softirq(SCHED_SOFTIRQ);
+#ifdef CONFIG_NO_HZ
+	else if (nohz_kick_needed(rq, cpu) && likely(!on_null_domain(cpu)))
+		nohz_balancer_kick(cpu);
+#endif
 }
 
 static void rq_online_fair(struct rq *rq)