[patch 5/7] sched: Change select_nohz_load_balancer to return void

[Suresh Siddha <suresh.b.siddha@intel.com>]

[-- Attachment #1: sched_select_nohz_load_balancer_to_return_void.patch --]
[-- Type: text/plain, Size: 3722 bytes --]

From: Venkatesh Pallipadi <venki@google.com>
Subject: sched: Change select_nohz_load_balancer to return void

select_nohz_load_balancer used to return 1 when ticks are not to be
stopped (idle_balancer), 0 otherwise. With change to nohz idle_balancer logic,
all idle cpus can go to tickless mode and be woken up by a kick from one
of the busy cpus, if and when idle balancing is required. As a result,
select_nohz_load_balancer can return void.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
---
 include/linux/sched.h    |    7 ++-----
 kernel/sched_fair.c      |   16 ++++++++--------
 kernel/time/tick-sched.c |    8 +-------
 3 files changed, 11 insertions(+), 20 deletions(-)

Index: tip/kernel/sched_fair.c
===================================================================
--- tip.orig/kernel/sched_fair.c
+++ tip/kernel/sched_fair.c
@@ -3266,14 +3266,14 @@ static void nohz_balancer_kick(int cpu)
  * ilb owner CPU in future (when there is a need for idle load balancing on
  * behalf of all idle CPUs).
  */
-int select_nohz_load_balancer(int stop_tick)
+void select_nohz_load_balancer(int stop_tick)
 {
 	int cpu = smp_processor_id();
 
 	if (stop_tick) {
 		if (!cpu_active(cpu)) {
 			if (atomic_read(&nohz.load_balancer) != cpu)
-				return 0;
+				return;
 
 			/*
 			 * If we are going offline and still the leader,
@@ -3282,7 +3282,7 @@ int select_nohz_load_balancer(int stop_t
 			if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
 				BUG();
 
-			return 0;
+			return;
 		}
 
 		cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
@@ -3297,7 +3297,7 @@ int select_nohz_load_balancer(int stop_t
 
 			/* make me the ilb owner */
 			if (atomic_cmpxchg(&nohz.load_balancer, -1, cpu) != -1)
-				return 0;
+				return;
 
 			/*
 			 * Check to see if there is a more power-efficient
@@ -3307,13 +3307,13 @@ int select_nohz_load_balancer(int stop_t
 			if (new_ilb < nr_cpu_ids && new_ilb != cpu) {
 				atomic_set(&nohz.load_balancer, -1);
 				resched_cpu(new_ilb);
-				return 0;
+				return;
 			}
-			return 0;
+			return;
 		}
 	} else {
 		if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
-			return 0;
+			return;
 
 		cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
 
@@ -3321,7 +3321,7 @@ int select_nohz_load_balancer(int stop_t
 			if (atomic_cmpxchg(&nohz.load_balancer, cpu, -1) != cpu)
 				BUG();
 	}
-	return 0;
+	return;
 }
 #endif
 
Index: tip/kernel/time/tick-sched.c
===================================================================
--- tip.orig/kernel/time/tick-sched.c
+++ tip/kernel/time/tick-sched.c
@@ -408,13 +408,7 @@ void tick_nohz_stop_sched_tick(int inidl
 		 * the scheduler tick in nohz_restart_sched_tick.
 		 */
 		if (!ts->tick_stopped) {
-			if (select_nohz_load_balancer(1)) {
-				/*
-				 * sched tick not stopped!
-				 */
-				cpumask_clear_cpu(cpu, nohz_cpu_mask);
-				goto out;
-			}
+			select_nohz_load_balancer(1);
 
 			ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
 			ts->tick_stopped = 1;
Index: tip/include/linux/sched.h
===================================================================
--- tip.orig/include/linux/sched.h
+++ tip/include/linux/sched.h
@@ -272,14 +272,11 @@ extern void task_rq_unlock_wait(struct t
 
 extern cpumask_var_t nohz_cpu_mask;
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)
-extern int select_nohz_load_balancer(int cpu);
+extern void select_nohz_load_balancer(int stop_tick);
 extern int get_nohz_load_balancer(void);
 extern int nohz_ratelimit(int cpu);
 #else
-static inline int select_nohz_load_balancer(int cpu)
-{
-	return 0;
-}
+static inline void select_nohz_load_balancer(int stop_tick) { }
 
 static inline int nohz_ratelimit(int cpu)
 {