---

yaml
---
r: 277388
b: refs/heads/master
c: 0b005cf
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 69e1e811dcc436a6b129dbef273ad9ec22d095ce
+refs/heads/master: 0b005cf54eac170a8f22540ab096a6e07bf49e7c

trunk/kernel/sched/fair.c

@@ -4727,28 +4727,17 @@ static int active_load_balance_cpu_stop(void *data)
 #ifdef CONFIG_NO_HZ
 /*
  * 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;
-	atomic_t first_pick_cpu;
-	atomic_t second_pick_cpu;
 	cpumask_var_t idle_cpus_mask;
 	cpumask_var_t grp_idle_mask;
+	atomic_t nr_cpus;
 	unsigned long next_balance;     /* in jiffy units */
 } nohz ____cacheline_aligned;
 
-int get_nohz_load_balancer(void)
-{
-	return atomic_read(&nohz.load_balancer);
-}
-
 #if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
 /**
  * lowest_flag_domain - Return lowest sched_domain containing flag.
@@ -4825,9 +4814,9 @@ static inline int is_semi_idle_group(struct sched_group *ilb_group)
  */
 static int find_new_ilb(int cpu)
 {
+	int ilb = cpumask_first(nohz.idle_cpus_mask);
 	struct sched_domain *sd;
 	struct sched_group *ilb_group;
-	int ilb = nr_cpu_ids;
 
 	/*
 	 * Have idle load balancer selection from semi-idle packages only
@@ -4881,13 +4870,10 @@ static void nohz_balancer_kick(int cpu)
 
 	nohz.next_balance++;
 
-	ilb_cpu = get_nohz_load_balancer();
+	ilb_cpu = find_new_ilb(cpu);
 
-	if (ilb_cpu >= nr_cpu_ids) {
-		ilb_cpu = cpumask_first(nohz.idle_cpus_mask);
-		if (ilb_cpu >= nr_cpu_ids)
-			return;
-	}
+	if (ilb_cpu >= nr_cpu_ids)
+		return;
 
 	if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)))
 		return;
@@ -4932,77 +4918,20 @@ void set_cpu_sd_state_idle(void)
 }
 
 /*
- * 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.
- *
- * 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.
- *
- * 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).
+ * This routine will record that this cpu is going idle with tick stopped.
+ * This info will be used in performing idle load balancing in the future.
  */
 void select_nohz_load_balancer(int stop_tick)
 {
 	int cpu = smp_processor_id();
 
 	if (stop_tick) {
-		if (!cpu_active(cpu)) {
-			if (atomic_read(&nohz.load_balancer) != cpu)
-				return;
-
-			/*
-			 * If we are going offline and still the leader,
-			 * give up!
-			 */
-			if (atomic_cmpxchg(&nohz.load_balancer, cpu,
-					   nr_cpu_ids) != cpu)
-				BUG();
-
+		if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
 			return;
-		}
 
 		cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
-
-		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) >= nr_cpu_ids) {
-			int new_ilb;
-
-			/* 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, nr_cpu_ids);
-				resched_cpu(new_ilb);
-				return;
-			}
-			return;
-		}
-
+		atomic_inc(&nohz.nr_cpus);
 		set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
-	} else {
-		if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
-			return;
-
-		cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
-
-		if (atomic_read(&nohz.load_balancer) == cpu)
-			if (atomic_cmpxchg(&nohz.load_balancer, cpu,
-					   nr_cpu_ids) != cpu)
-				BUG();
 	}
 	return;
 }
@@ -5113,7 +5042,7 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
 		goto end;
 
 	for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
-		if (balance_cpu == this_cpu)
+		if (balance_cpu == this_cpu || !idle_cpu(this_cpu))
 			continue;
 
 		/*
@@ -5141,22 +5070,18 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
 }
 
 /*
- * 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.
+ * Current heuristic for kicking the idle load balancer in the presence
+ * of an idle cpu is the system.
+ *   - This rq has more than one task.
+ *   - At any scheduler domain level, this cpu's scheduler group has multiple
+ *     busy cpu's exceeding the group's power.
+ *   - For SD_ASYM_PACKING, if the lower numbered cpu's in the scheduler
+ *     domain span are idle.
  */
 static inline int nohz_kick_needed(struct rq *rq, int cpu)
 {
 	unsigned long now = jiffies;
-	int ret;
-	int first_pick_cpu, second_pick_cpu;
+	struct sched_domain *sd;
 
 	if (unlikely(idle_cpu(cpu)))
 		return 0;
@@ -5166,32 +5091,44 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
 	* busy tick after returning from idle, we will update the busy stats.
 	*/
 	set_cpu_sd_state_busy();
-	if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu))))
+	if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
 		clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
+		cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
+		atomic_dec(&nohz.nr_cpus);
+	}
+
+	/*
+	 * None are in tickless mode and hence no need for NOHZ idle load
+	 * balancing.
+	 */
+	if (likely(!atomic_read(&nohz.nr_cpus)))
+		return 0;
 
 	if (time_before(now, nohz.next_balance))
 		return 0;
 
-	first_pick_cpu = atomic_read(&nohz.first_pick_cpu);
-	second_pick_cpu = atomic_read(&nohz.second_pick_cpu);
+	if (rq->nr_running >= 2)
+		goto need_kick;
 
-	if (first_pick_cpu < nr_cpu_ids && first_pick_cpu != cpu &&
-	    second_pick_cpu < nr_cpu_ids && second_pick_cpu != cpu)
-		return 0;
+	for_each_domain(cpu, sd) {
+		struct sched_group *sg = sd->groups;
+		struct sched_group_power *sgp = sg->sgp;
+		int nr_busy = atomic_read(&sgp->nr_busy_cpus);
 
-	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;
-		}
+		if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1)
+			goto need_kick;
+
+		if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight
+		    && (cpumask_first_and(nohz.idle_cpus_mask,
+					  sched_domain_span(sd)) < cpu))
+			goto need_kick;
+
+		if (!(sd->flags & (SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING)))
+			break;
 	}
 	return 0;
+need_kick:
+	return 1;
 }
 #else
 static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle) { }
@@ -5652,9 +5589,6 @@ __init void init_sched_fair_class(void)
 #ifdef CONFIG_NO_HZ
 	zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
 	alloc_cpumask_var(&nohz.grp_idle_mask, GFP_NOWAIT);
-	atomic_set(&nohz.load_balancer, nr_cpu_ids);
-	atomic_set(&nohz.first_pick_cpu, nr_cpu_ids);
-	atomic_set(&nohz.second_pick_cpu, nr_cpu_ids);
 #endif
 #endif /* SMP */