sched/headers: Move the NOHZ APIs from <linux/sched.h> to <linux/sched/nohz.h>

There's a number of NOHZ/dyntics related functionality in <linux/sched.h>,
but only a handful of timer files are making use of them.

Move them into their own header. This better documents these APIs
and unclutters <linux/sched.h>.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched.h

@@ -46,14 +46,6 @@ struct nameidata;
 struct signal_struct;
 struct sighand_struct;
 
-#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
-extern void cpu_load_update_nohz_start(void);
-extern void cpu_load_update_nohz_stop(void);
-#else
-static inline void cpu_load_update_nohz_start(void) { }
-static inline void cpu_load_update_nohz_stop(void) { }
-#endif
-
 extern void dump_cpu_task(int cpu);
 
 struct seq_file;
@@ -204,15 +196,6 @@ extern cpumask_var_t cpu_isolated_map;
 
 extern int runqueue_is_locked(int cpu);
 
-#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
-extern void nohz_balance_enter_idle(int cpu);
-extern void set_cpu_sd_state_idle(void);
-extern int get_nohz_timer_target(void);
-#else
-static inline void nohz_balance_enter_idle(int cpu) { }
-static inline void set_cpu_sd_state_idle(void) { }
-#endif
-
 /*
  * Only dump TASK_* tasks. (0 for all tasks)
  */
@@ -1535,14 +1518,6 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p,
 }
 #endif
 
-#ifdef CONFIG_NO_HZ_COMMON
-void calc_load_enter_idle(void);
-void calc_load_exit_idle(void);
-#else
-static inline void calc_load_enter_idle(void) { }
-static inline void calc_load_exit_idle(void) { }
-#endif /* CONFIG_NO_HZ_COMMON */
-
 #ifndef cpu_relax_yield
 #define cpu_relax_yield() cpu_relax()
 #endif
@@ -1563,16 +1538,6 @@ extern void idle_task_exit(void);
 static inline void idle_task_exit(void) {}
 #endif
 
-#if defined(CONFIG_NO_HZ_COMMON) && defined(CONFIG_SMP)
-extern void wake_up_nohz_cpu(int cpu);
-#else
-static inline void wake_up_nohz_cpu(int cpu) { }
-#endif
-
-#ifdef CONFIG_NO_HZ_FULL
-extern u64 scheduler_tick_max_deferment(void);
-#endif
-
 extern int yield_to(struct task_struct *p, bool preempt);
 extern void set_user_nice(struct task_struct *p, long nice);
 extern int task_prio(const struct task_struct *p);

include/linux/sched/nohz.h

@@ -3,4 +3,43 @@
 
 #include <linux/sched.h>
 
+/*
+ * This is the interface between the scheduler and nohz/dyntics:
+ */
+
+#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+extern void cpu_load_update_nohz_start(void);
+extern void cpu_load_update_nohz_stop(void);
+#else
+static inline void cpu_load_update_nohz_start(void) { }
+static inline void cpu_load_update_nohz_stop(void) { }
+#endif
+
+#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+extern void nohz_balance_enter_idle(int cpu);
+extern void set_cpu_sd_state_idle(void);
+extern int get_nohz_timer_target(void);
+#else
+static inline void nohz_balance_enter_idle(int cpu) { }
+static inline void set_cpu_sd_state_idle(void) { }
+#endif
+
+#ifdef CONFIG_NO_HZ_COMMON
+void calc_load_enter_idle(void);
+void calc_load_exit_idle(void);
+#else
+static inline void calc_load_enter_idle(void) { }
+static inline void calc_load_exit_idle(void) { }
+#endif /* CONFIG_NO_HZ_COMMON */
+
+#if defined(CONFIG_NO_HZ_COMMON) && defined(CONFIG_SMP)
+extern void wake_up_nohz_cpu(int cpu);
+#else
+static inline void wake_up_nohz_cpu(int cpu) { }
+#endif
+
+#ifdef CONFIG_NO_HZ_FULL
+extern u64 scheduler_tick_max_deferment(void);
+#endif
+
 #endif /* _LINUX_SCHED_NOHZ_H */