sched: Move rq->idle_stamp up to the core

idle_balance() modifies the rq->idle_stamp field, making this information
shared across core.c and fair.c.

As we know if the cpu is going to idle or not with the previous patch, let's
encapsulate the rq->idle_stamp information in core.c by moving it up to the
caller.

The idle_balance() function returns true in case a balancing occured and the
cpu won't be idle, false if no balance happened and the cpu is going idle.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: alex.shi@linaro.org
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1389949444-14821-3-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 16 insertions, 11 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 74dd565c2e1b..417cf657a606 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2704,8 +2704,15 @@ need_resched:
 
         pre_schedule(rq, prev);
 
-        if (unlikely(!rq->nr_running))
-                idle_balance(rq);
+        if (unlikely(!rq->nr_running)) {
+                /*
+                 * We must set idle_stamp _before_ calling idle_balance(), such
+                 * that we measure the duration of idle_balance() as idle time.
+                 */
+                rq->idle_stamp = rq_clock(rq);
+                if (idle_balance(rq))
+                        rq->idle_stamp = 0;
+        }
 
         put_prev_task(rq, prev);
         next = pick_next_task(rq);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5ebc6817c036..04fea7744a9f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6531,7 +6531,7 @@ out:
  * idle_balance is called by schedule() if this_cpu is about to become
  * idle. Attempts to pull tasks from other CPUs.
  */
-void idle_balance(struct rq *this_rq)
+int idle_balance(struct rq *this_rq)
 {
         struct sched_domain *sd;
         int pulled_task = 0;
@@ -6539,10 +6539,8 @@ void idle_balance(struct rq *this_rq)
         u64 curr_cost = 0;
         int this_cpu = this_rq->cpu;
 
-        this_rq->idle_stamp = rq_clock(this_rq);
-
         if (this_rq->avg_idle < sysctl_sched_migration_cost)
-                return;
+                return 0;
 
         /*
          * Drop the rq->lock, but keep IRQ/preempt disabled.
@@ -6580,10 +6578,8 @@ void idle_balance(struct rq *this_rq)
                 interval = msecs_to_jiffies(sd->balance_interval);
                 if (time_after(next_balance, sd->last_balance + interval))
                         next_balance = sd->last_balance + interval;
-                if (pulled_task) {
-                        this_rq->idle_stamp = 0;
+                if (pulled_task)
                         break;
-                }
         }
         rcu_read_unlock();
 
@@ -6594,7 +6590,7 @@ void idle_balance(struct rq *this_rq)
          * A task could have be enqueued in the meantime
          */
         if (this_rq->nr_running && !pulled_task)
-                return;
+                return 1;
 
         if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
                 /*
@@ -6606,6 +6602,8 @@ void idle_balance(struct rq *this_rq)
 
         if (curr_cost > this_rq->max_idle_balance_cost)
                 this_rq->max_idle_balance_cost = curr_cost;
+
+        return pulled_task;
 }
 
 /*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 82c0e02f2a58..bb89991ee409 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1158,7 +1158,7 @@ extern const struct sched_class idle_sched_class;
 extern void update_group_power(struct sched_domain *sd, int cpu);
 
 extern void trigger_load_balance(struct rq *rq);
-extern void idle_balance(struct rq *this_rq);
+extern int idle_balance(struct rq *this_rq);
 
 extern void idle_enter_fair(struct rq *this_rq);
 extern void idle_exit_fair(struct rq *this_rq);