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Date: Wed, 9 May 2012 07:27:21 -0700
From: tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
a.p.zijlstra@...llo.nl, tglx@...utronix.de
Subject: [tip:sched/core] sched/fair:
Add some serialization to the sched_domain load-balance walk
Commit-ID: 0ce90475dcdbe90affc218e9688c8401e468e84d
Gitweb: http://git.kernel.org/tip/0ce90475dcdbe90affc218e9688c8401e468e84d
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Wed, 25 Apr 2012 00:30:36 +0200
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 9 May 2012 15:00:53 +0200
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: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/n/tip-vqh9ai6s0ewmeakjz80w4qz6@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 2 ++
kernel/sched/fair.c | 9 +++++++--
3 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4a559bf..3cbfb55 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -927,6 +927,7 @@ struct sched_group_power {
struct sched_group {
struct sched_group *next; /* Must be a circular list */
atomic_t ref;
+ int balance_cpu;
unsigned int group_weight;
struct sched_group_power *sgp;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0533a68..6001e5c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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));
atomic_inc(&sg->sgp->ref);
+ sg->balance_cpu = -1;
if (cpumask_test_cpu(cpu, sg_span))
groups = sg;
@@ -6135,6 +6136,7 @@ build_sched_groups(struct sched_domain *sd, int cpu)
cpumask_clear(sched_group_cpus(sg));
sg->sgp->power = 0;
+ sg->balance_cpu = -1;
for_each_cpu(j, span) {
if (get_group(j, sdd, NULL) != group)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 968ffee..cf86f74 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3828,7 +3828,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
*/
if (local_group) {
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;
return;
}
@@ -4929,7 +4930,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
int balance = 1;
struct rq *rq = cpu_rq(cpu);
unsigned long interval;
- struct sched_domain *sd;
+ struct sched_domain *sd, *last = NULL;
/* Earliest time when we have to do rebalance again */
unsigned long next_balance = jiffies + 60*HZ;
int update_next_balance = 0;
@@ -4939,6 +4940,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
rcu_read_lock();
for_each_domain(cpu, sd) {
+ last = sd;
if (!(sd->flags & SD_LOAD_BALANCE))
continue;
@@ -4983,6 +4985,9 @@ out:
if (!balance)
break;
}
+ for (sd = last; sd; sd = sd->child)
+ (void)cmpxchg(&sd->groups->balance_cpu, cpu, -1);
+
rcu_read_unlock();
/*
--
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