[RFC PATCH v3 12/13] sched/fair: Allocate nohz.idle_cpus_mask during sched_init_smp()

[K Prateek Nayak]

nohz.idle_cpus_mask is not required soon after early initialization
since the boot CPU cannot go tickless idle before CPU is activated and
tick is started.

Defer allocation of nohz.idle_cpus_mask to sched_init_smp() via
init_sched_fair_class_smp(). This is preparation to convert
nohz.idle_cpus_mask to sparsebitmap (sbm) which requires architectures
to finish smp_prepare before initializing the core bits.

No functional changes intended.

Signed-off-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
---
 kernel/sched/core.c  | 2 ++
 kernel/sched/fair.c  | 8 +++++++-
 kernel/sched/sched.h | 1 +
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 977f579da410..127aed81d316 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8849,6 +8849,8 @@ int sched_cpu_dying(unsigned int cpu)
 
 void __init sched_init_smp(void)
 {
+	init_sched_fair_class_smp();
+
 	sched_init_numa(NUMA_NO_NODE);
 
 	prandom_init_once(&sched_rnd_state);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1c687c3c70f1..a0a659f4c3be 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -15645,6 +15645,13 @@ void show_numa_stats(struct task_struct *p, struct seq_file *m)
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
+__init void init_sched_fair_class_smp(void)
+{
+#ifdef CONFIG_NO_HZ_COMMON
+	zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
+#endif
+}
+
 __init void init_sched_fair_class(void)
 {
 	int i;
@@ -15666,6 +15673,5 @@ __init void init_sched_fair_class(void)
 #ifdef CONFIG_NO_HZ_COMMON
 	nohz.next_balance = jiffies;
 	nohz.next_blocked = jiffies;
-	zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
 #endif
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 7d2ec527b8a2..0726e8fb5967 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3024,6 +3024,7 @@ extern void update_max_interval(void);
 extern void init_sched_dl_class(void);
 extern void init_sched_rt_class(void);
 extern void init_sched_fair_class(void);
+extern void init_sched_fair_class_smp(void);
 
 extern void resched_curr(struct rq *rq);
 extern void resched_curr_lazy(struct rq *rq);
-- 
2.34.1