From: "Siddha, Suresh B" 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 Signed-off-by: Andrew Morton --- kernel/sched.c | 14 ++++++++++++-- 1 files changed, 12 insertions(+), 2 deletions(-) diff -puN kernel/sched.c~sched-skip-updating-rqs-next_balance-under-null-sd kernel/sched.c --- a/kernel/sched.c~sched-skip-updating-rqs-next_balance-under-null-sd +++ a/kernel/sched.c @@ -3020,6 +3020,7 @@ static inline void rebalance_domains(int 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 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; } /* _