[RFC PATCH 02/18] sched/isolation: Call sched_tick_offload_init() when HK_FLAG_KERNEL_NOISE is first set

[Waiman Long]

The sched_tick_offload_init() function is called at boot time whenever
"nohz_full" is set. Now housekeeping cpumasks can be updated at run
time without the corresponding "nohz_full" kernel parameter. So we have
to be able to call sched_tick_offload_init() at run time to allow tick
offloading. Remove the __init attribute from sched_tick_offload_init()
and call it when the HK_FLAG_KERNEL_NOISE flag is first set.

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 kernel/sched/core.c      |  2 +-
 kernel/sched/isolation.c | 10 +++++++++-
 kernel/sched/sched.h     |  2 +-
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index be00629f0ba4..9f02c047e25b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5783,7 +5783,7 @@ static void sched_tick_stop(int cpu)
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
-int __init sched_tick_offload_init(void)
+int sched_tick_offload_init(void)
 {
 	tick_work_cpu = alloc_percpu(struct tick_work);
 	BUG_ON(!tick_work_cpu);
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 3fb0e8ccce26..ee396ae13719 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -33,6 +33,7 @@ struct housekeeping {
 };
 
 static struct housekeeping housekeeping;
+static bool sched_tick_offload_inited;
 
 bool housekeeping_enabled(enum hk_type type)
 {
@@ -103,8 +104,10 @@ void __init housekeeping_init(void)
 
 	static_branch_enable(&housekeeping_overridden);
 
-	if (housekeeping.flags & HK_FLAG_KERNEL_NOISE)
+	if (housekeeping.flags & HK_FLAG_KERNEL_NOISE) {
 		sched_tick_offload_init();
+		sched_tick_offload_inited = true;
+	}
 
 	for_each_set_bit(type, &housekeeping.flags, HK_TYPE_MAX) {
 		/* We need at least one CPU to handle housekeeping work */
@@ -324,5 +327,10 @@ int housekeeping_exclude_cpumask(struct cpumask *cpumask, unsigned long hk_flags
 		static_key_disable(&housekeeping_overridden.key);
 	else if (housekeeping.flags && !static_key_enabled(&housekeeping_overridden))
 		static_key_enable(&housekeeping_overridden.key);
+
+	if ((housekeeping.flags & HK_FLAG_KERNEL_NOISE) && !sched_tick_offload_inited) {
+		sched_tick_offload_init();
+		sched_tick_offload_inited = true;
+	}
 	return 0;
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index be9745d104f7..d4676305e099 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2671,7 +2671,7 @@ extern void post_init_entity_util_avg(struct task_struct *p);
 
 #ifdef CONFIG_NO_HZ_FULL
 extern bool sched_can_stop_tick(struct rq *rq);
-extern int __init sched_tick_offload_init(void);
+extern int sched_tick_offload_init(void);
 
 /*
  * Tick may be needed by tasks in the runqueue depending on their policy and
-- 
2.50.0