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@chello.nl>
Link: http://lkml.kernel.org/n/tip-vqh9ai6s0ewmeakjz80w4qz6@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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 @@
*/
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 @@
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 @@
rcu_read_lock();
for_each_domain(cpu, sd) {
+ last = sd;
if (!(sd->flags & SD_LOAD_BALANCE))
continue;
@@ -4983,6 +4985,9 @@
if (!balance)
break;
}
+ for (sd = last; sd; sd = sd->child)
+ (void)cmpxchg(&sd->groups->balance_cpu, cpu, -1);
+
rcu_read_unlock();
/*