sched: Fix nohz_idle_balance()

On tickless systems, one CPU runs load balance for all idle CPUs.

The cpu_load of this CPU is updated before starting the load balance
of each other idle CPUs. We should instead update the cpu_load of
the balance_cpu.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1347509486-8688-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ca4fe423528..9ae3a5b68ba4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4794,14 +4794,15 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
                 if (need_resched())
                         break;
 
-                raw_spin_lock_irq(&this_rq->lock);
-                update_rq_clock(this_rq);
-                update_idle_cpu_load(this_rq);
-                raw_spin_unlock_irq(&this_rq->lock);
+                rq = cpu_rq(balance_cpu);
+
+                raw_spin_lock_irq(&rq->lock);
+                update_rq_clock(rq);
+                update_idle_cpu_load(rq);
+                raw_spin_unlock_irq(&rq->lock);
 
                 rebalance_domains(balance_cpu, CPU_IDLE);
 
-                rq = cpu_rq(balance_cpu);
                 if (time_after(this_rq->next_balance, rq->next_balance))
                         this_rq->next_balance = rq->next_balance;
         }