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



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