sched: Make set_cpu_rq_start_time() a built in hotplug state

Start distangling the maze of hotplug notifiers in the scheduler.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Cc: rt@linutronix.de
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/linux/cpuhotplug.h

@@ -8,6 +8,7 @@ enum cpuhp_state {
 	CPUHP_BRINGUP_CPU,
 	CPUHP_AP_IDLE_DEAD,
 	CPUHP_AP_OFFLINE,
+	CPUHP_AP_SCHED_STARTING,
 	CPUHP_AP_NOTIFY_STARTING,
 	CPUHP_AP_ONLINE,
 	CPUHP_TEARDOWN_CPU,

include/linux/sched.h

@@ -372,6 +372,7 @@ extern void cpu_init (void);
 extern void trap_init(void);
 extern void update_process_times(int user);
 extern void scheduler_tick(void);
+extern int sched_cpu_starting(unsigned int cpu);
 
 extern void sched_show_task(struct task_struct *p);
 

kernel/cpu.c

@@ -1236,6 +1236,12 @@ static struct cpuhp_step cpuhp_ap_states[] = {
 		.name			= "ap:offline",
 		.cant_stop		= true,
 	},
+	/* First state is scheduler control. Interrupts are disabled */
+	[CPUHP_AP_SCHED_STARTING] = {
+		.name			= "sched:starting",
+		.startup		= sched_cpu_starting,
+		.teardown		= NULL,
+	},
 	/*
 	 * Low level startup/teardown notifiers. Run with interrupts
 	 * disabled. Will be removed once the notifiers are converted to

kernel/sched/core.c

@@ -5473,10 +5473,10 @@ static struct notifier_block migration_notifier = {
 	.priority = CPU_PRI_MIGRATION,
 };
 
-static void set_cpu_rq_start_time(void)
+static void set_cpu_rq_start_time(unsigned int cpu)
 {
-	int cpu = smp_processor_id();
 	struct rq *rq = cpu_rq(cpu);
+
 	rq->age_stamp = sched_clock_cpu(cpu);
 }
 
@@ -5486,10 +5486,6 @@ static int sched_cpu_active(struct notifier_block *nfb,
 	int cpu = (long)hcpu;
 
 	switch (action & ~CPU_TASKS_FROZEN) {
-	case CPU_STARTING:
-		set_cpu_rq_start_time();
-		return NOTIFY_OK;
-
 	case CPU_DOWN_FAILED:
 		set_cpu_active(cpu, true);
 		return NOTIFY_OK;
@@ -5511,6 +5507,12 @@ static int sched_cpu_inactive(struct notifier_block *nfb,
 	}
 }
 
+int sched_cpu_starting(unsigned int cpu)
+{
+	set_cpu_rq_start_time(cpu);
+	return 0;
+}
+
 static int __init migration_init(void)
 {
 	void *cpu = (void *)(long)smp_processor_id();
@@ -7426,7 +7428,7 @@ void __init sched_init(void)
 	if (cpu_isolated_map == NULL)
 		zalloc_cpumask_var(&cpu_isolated_map, GFP_NOWAIT);
 	idle_thread_set_boot_cpu();
-	set_cpu_rq_start_time();
+	set_cpu_rq_start_time(smp_processor_id());
 #endif
 	init_sched_fair_class();