[patch] sched: skip updating rq's next_balance under null SD

Siddha, Suresh B
2007-08-16T01:11:27Z

Was playing with sched_smt_power_savings/sched_mc_power_savings and found
out that while the scheduler domains are reconstructed when sysfs settings
change, rebalance_domains() can get triggered with null domain on other cpus,
which is setting next_balance to jiffies + 60*HZ. Resulting in no idle/busy
balancing for 60 seconds.

Fix this.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---

diff --git a/kernel/sched.c b/kernel/sched.c
index 45e17b8..74565c0 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3020,6 +3020,7 @@ static inline void rebalance_domains(int cpu, enum cpu_idle_type idle)
struct sched_domain *sd;
/* Earliest time when we have to do rebalance again */
unsigned long next_balance = jiffies + 60*HZ;
+ int update_next_balance = 0;

for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
@@ -3056,8 +3057,10 @@ static inline void rebalance_domains(int cpu, enum cpu_idle_type idle)
if (sd->flags & SD_SERIALIZE)
spin_unlock(&balancing);
out:
- if (time_after(next_balance, sd->last_balance + interval))
+ if (time_after(next_balance, sd->last_balance + interval)) {
next_balance = sd->last_balance + interval;
+ update_next_balance = 1;
+ }

/*
* Stop the load balance at this level. There is another
@@ -3067,7 +3070,14 @@ out:
if (!balance)
break;
}
- rq->next_balance = next_balance;
+
+ /*
+ * next_balance will be updated only when there is a need.
+ * When the cpu is attached to null domain for ex, it will not be
+ * updated.
+ */
+ if (likely(update_next_balance))
+ rq->next_balance = next_balance;
}

/*