sched: cleanup wake_idle power saving

Hopefully a more readable version of the same.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Dinakar Guniguntala <dino@in.ibm.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Darren Hart <dvhltc@us.ibm.com>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/sched_fair.c

@@ -1040,6 +1040,41 @@ static void yield_task_fair(struct rq *rq)
 	se->vruntime = rightmost->vruntime + 1;
 }
 
+#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
+/*
+ * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
+ * are idle and this is not a kernel thread and this task's affinity
+ * allows it to be moved to preferred cpu, then just move!
+ *
+ * XXX - can generate significant overload on perferred_wakeup_cpu
+ *       with plenty of idle cpus, leading to a significant loss in
+ *       throughput.
+ *
+ * Returns: <  0 - no placement decision made
+ *          >= 0 - place on cpu
+ */
+static int wake_idle_power_save(int cpu, struct task_struct *p)
+{
+	int this_cpu = smp_processor_id();
+	int wakeup_cpu;
+
+	if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
+		return -1;
+
+	if (!idle_cpu(cpu) || !idle_cpu(this_cpu))
+		return -1;
+
+	if (!p->mm || (p->flags & PF_KTHREAD))
+		return -1;
+
+	wakeup_cpu = cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;
+
+	if (!cpu_isset(wakeup_cpu, p->cpus_allowed))
+		return -1;
+
+	return wakeup_cpu;
+}
+
 /*
  * wake_idle() will wake a task on an idle cpu if task->cpu is
  * not idle and an idle cpu is available.  The span of cpus to
@@ -1050,29 +1085,14 @@ static void yield_task_fair(struct rq *rq)
  *
  * Returns the CPU we should wake onto.
  */
-#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
 static int wake_idle(int cpu, struct task_struct *p)
 {
 	struct sched_domain *sd;
 	int i;
-	unsigned int chosen_wakeup_cpu;
-	int this_cpu;
-
-	/*
-	 * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
-	 * are idle and this is not a kernel thread and this task's affinity
-	 * allows it to be moved to preferred cpu, then just move!
-	 */
-
-	this_cpu = smp_processor_id();
-	chosen_wakeup_cpu =
-		cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;
 
-	if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP &&
-		idle_cpu(cpu) && idle_cpu(this_cpu) &&
-		p->mm && !(p->flags & PF_KTHREAD) &&
-		cpu_isset(chosen_wakeup_cpu, p->cpus_allowed))
-		return chosen_wakeup_cpu;
+	i = wake_idle_power_save(cpu, p);
+	if (i >= 0)
+		return i;
 
 	/*
 	 * If it is idle, then it is the best cpu to run this task.
@@ -1081,7 +1101,7 @@ static int wake_idle(int cpu, struct task_struct *p)
 	 * Siblings must be also busy(in most cases) as they didn't already
 	 * pickup the extra load from this cpu and hence we need not check
 	 * sibling runqueue info. This will avoid the checks and cache miss
-	 * penalities associated with that.
+	 * penalties associated with that.
 	 */
 	if (idle_cpu(cpu) || cpu_rq(cpu)->cfs.nr_running > 1)
 		return cpu;