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Commit 0ce90475 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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sched/fair: Add some serialization to the sched_domain load-balance walk 



Since the sched_domain walk is completely unserialized (!SD_SERIALIZE)
it is possible that multiple cpus in the group get elected to do the
next level. Avoid this by adding some serialization.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-vqh9ai6s0ewmeakjz80w4qz6@git.kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c22402a2

include/linux/sched.h

+1 −0
Original line number Original line Diff line number Diff line
@@ -927,6 +927,7 @@ struct sched_group_power { 
struct sched_group {

struct sched_group {

	struct sched_group *next;	/* Must be a circular list */

	struct sched_group *next;	/* Must be a circular list */

	atomic_t ref;

	atomic_t ref;

	int balance_cpu;





	unsigned int group_weight;

	unsigned int group_weight;

	struct sched_group_power *sgp;

	struct sched_group_power *sgp;

kernel/sched/core.c

+2 −0
Original line number Original line Diff line number Diff line
@@ -6060,6 +6060,7 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu) 




		sg->sgp = *per_cpu_ptr(sdd->sgp, cpumask_first(sg_span));

		sg->sgp = *per_cpu_ptr(sdd->sgp, cpumask_first(sg_span));

		atomic_inc(&sg->sgp->ref);

		atomic_inc(&sg->sgp->ref);

		sg->balance_cpu = -1;





		if (cpumask_test_cpu(cpu, sg_span))

		if (cpumask_test_cpu(cpu, sg_span))

			groups = sg;

			groups = sg;
@@ -6135,6 +6136,7 @@ build_sched_groups(struct sched_domain *sd, int cpu) 




		cpumask_clear(sched_group_cpus(sg));

		cpumask_clear(sched_group_cpus(sg));

		sg->sgp->power = 0;

		sg->sgp->power = 0;

		sg->balance_cpu = -1;





		for_each_cpu(j, span) {

		for_each_cpu(j, span) {

			if (get_group(j, sdd, NULL) != group)

			if (get_group(j, sdd, NULL) != group)

kernel/sched/fair.c

+7 −2
Original line number Original line Diff line number Diff line
@@ -3828,7 +3828,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd, 
	 */

	 */

	if (local_group) {

	if (local_group) {

		if (idle != CPU_NEWLY_IDLE) {

		if (idle != CPU_NEWLY_IDLE) {

			if (balance_cpu != this_cpu) {

			if (balance_cpu != this_cpu ||

			    cmpxchg(&group->balance_cpu, -1, balance_cpu) != -1) {

				*balance = 0;

				*balance = 0;

				return;

				return;

			}

			}
@@ -4929,7 +4930,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle) 
	int balance = 1;

	int balance = 1;

	struct rq *rq = cpu_rq(cpu);

	struct rq *rq = cpu_rq(cpu);

	unsigned long interval;

	unsigned long interval;

	struct sched_domain *sd;

	struct sched_domain *sd, *last = NULL;

	/* Earliest time when we have to do rebalance again */

	/* Earliest time when we have to do rebalance again */

	unsigned long next_balance = jiffies + 60*HZ;

	unsigned long next_balance = jiffies + 60*HZ;

	int update_next_balance = 0;

	int update_next_balance = 0;
@@ -4939,6 +4940,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle) 




	rcu_read_lock();

	rcu_read_lock();

	for_each_domain(cpu, sd) {

	for_each_domain(cpu, sd) {

		last = sd;

		if (!(sd->flags & SD_LOAD_BALANCE))

		if (!(sd->flags & SD_LOAD_BALANCE))

			continue;

			continue;
@@ -4983,6 +4985,9 @@ out: 
		if (!balance)

		if (!balance)

			break;

			break;

	}

	}

	for (sd = last; sd; sd = sd->child)

		(void)cmpxchg(&sd->groups->balance_cpu, cpu, -1);



	rcu_read_unlock();

	rcu_read_unlock();





	/*

	/*