sched/smp: Make SMP unconditional

Simplify the scheduler by making CONFIG_SMP=y primitives and data
structures unconditional.

Introduce transitory wrappers for functionality not yet converted to SMP.

Note that this patch is pretty large, because there's no clear separation
between various aspects of the SMP scheduler, it's basically a huge block
of #ifdef CONFIG_SMP. A fair amount of it has to be switched on for it to
boot and work on UP systems.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250528080924.2273858-21-mingo@kernel.org

1 files changed, 3 insertions, 118 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 2bf804b8c89b..7a7ebc2a3675 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -443,14 +443,12 @@ struct task_group {
 	/* runqueue "owned" by this group on each CPU */
 	struct cfs_rq		**cfs_rq;
 	unsigned long		shares;
-#ifdef CONFIG_SMP
 	/*
 	 * load_avg can be heavily contended at clock tick time, so put
 	 * it in its own cache-line separated from the fields above which
 	 * will also be accessed at each tick.
 	 */
 	atomic_long_t		load_avg ____cacheline_aligned;
-#endif /* CONFIG_SMP */
 #endif /* CONFIG_FAIR_GROUP_SCHED */
 
 #ifdef CONFIG_RT_GROUP_SCHED
@@ -574,13 +572,8 @@ extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
 
 extern int sched_group_set_idle(struct task_group *tg, long idle);
 
-#ifdef CONFIG_SMP
 extern void set_task_rq_fair(struct sched_entity *se,
 			     struct cfs_rq *prev, struct cfs_rq *next);
-#else /* !CONFIG_SMP: */
-static inline void set_task_rq_fair(struct sched_entity *se,
-			     struct cfs_rq *prev, struct cfs_rq *next) { }
-#endif /* !CONFIG_SMP */
 #else /* !CONFIG_FAIR_GROUP_SCHED: */
 static inline int sched_group_set_shares(struct task_group *tg, unsigned long shares) { return 0; }
 static inline int sched_group_set_idle(struct task_group *tg, long idle) { return 0; }
@@ -668,7 +661,6 @@ struct cfs_rq {
 	struct sched_entity	*curr;
 	struct sched_entity	*next;
 
-#ifdef CONFIG_SMP
 	/*
 	 * CFS load tracking
 	 */
@@ -700,7 +692,6 @@ struct cfs_rq {
 	u64			last_h_load_update;
 	struct sched_entity	*h_load_next;
 #endif /* CONFIG_FAIR_GROUP_SCHED */
-#endif /* CONFIG_SMP */
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	struct rq		*rq;	/* CPU runqueue to which this cfs_rq is attached */
@@ -797,14 +788,10 @@ struct rt_rq {
 	struct rt_prio_array	active;
 	unsigned int		rt_nr_running;
 	unsigned int		rr_nr_running;
-#if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
 	struct {
 		int		curr; /* highest queued rt task prio */
-#ifdef CONFIG_SMP
 		int		next; /* next highest */
-#endif
 	} highest_prio;
-#endif
 #ifdef CONFIG_SMP
 	bool			overloaded;
 	struct plist_head	pushable_tasks;
@@ -840,7 +827,6 @@ struct dl_rq {
 
 	unsigned int		dl_nr_running;
 
-#ifdef CONFIG_SMP
 	/*
 	 * Deadline values of the currently executing and the
 	 * earliest ready task on this rq. Caching these facilitates
@@ -860,9 +846,7 @@ struct dl_rq {
 	 * of the leftmost (earliest deadline) element.
 	 */
 	struct rb_root_cached	pushable_dl_tasks_root;
-#else /* !CONFIG_SMP: */
-	struct dl_bw		dl_bw;
-#endif /* !CONFIG_SMP */
+
 	/*
 	 * "Active utilization" for this runqueue: increased when a
 	 * task wakes up (becomes TASK_RUNNING) and decreased when a
@@ -933,7 +917,6 @@ static inline long se_runnable(struct sched_entity *se)
 
 #endif /* !CONFIG_FAIR_GROUP_SCHED */
 
-#ifdef CONFIG_SMP
 /*
  * XXX we want to get rid of these helpers and use the full load resolution.
  */
@@ -1044,7 +1027,6 @@ static inline void set_rd_overloaded(struct root_domain *rd, int status)
 #ifdef HAVE_RT_PUSH_IPI
 extern void rto_push_irq_work_func(struct irq_work *work);
 #endif
-#endif /* CONFIG_SMP */
 
 #ifdef CONFIG_UCLAMP_TASK
 /*
@@ -1108,18 +1090,14 @@ struct rq {
 	unsigned int		numa_migrate_on;
 #endif
 #ifdef CONFIG_NO_HZ_COMMON
-#ifdef CONFIG_SMP
 	unsigned long		last_blocked_load_update_tick;
 	unsigned int		has_blocked_load;
 	call_single_data_t	nohz_csd;
-#endif /* CONFIG_SMP */
 	unsigned int		nohz_tick_stopped;
 	atomic_t		nohz_flags;
 #endif /* CONFIG_NO_HZ_COMMON */
 
-#ifdef CONFIG_SMP
 	unsigned int		ttwu_pending;
-#endif
 	u64			nr_switches;
 
 #ifdef CONFIG_UCLAMP_TASK
@@ -1184,7 +1162,6 @@ struct rq {
 	int membarrier_state;
 #endif
 
-#ifdef CONFIG_SMP
 	struct root_domain		*rd;
 	struct sched_domain __rcu	*sd;
 
@@ -1225,7 +1202,6 @@ struct rq {
 #ifdef CONFIG_HOTPLUG_CPU
 	struct rcuwait		hotplug_wait;
 #endif
-#endif /* CONFIG_SMP */
 
 #ifdef CONFIG_IRQ_TIME_ACCOUNTING
 	u64			prev_irq_time;
@@ -1272,9 +1248,7 @@ struct rq {
 	struct cpuidle_state	*idle_state;
 #endif
 
-#ifdef CONFIG_SMP
 	unsigned int		nr_pinned;
-#endif
 	unsigned int		push_busy;
 	struct cpu_stop_work	push_work;
 
@@ -1300,7 +1274,7 @@ struct rq {
 	/* Scratch cpumask to be temporarily used under rq_lock */
 	cpumask_var_t		scratch_mask;
 
-#if defined(CONFIG_CFS_BANDWIDTH) && defined(CONFIG_SMP)
+#ifdef CONFIG_CFS_BANDWIDTH
 	call_single_data_t	cfsb_csd;
 	struct list_head	cfsb_csd_list;
 #endif
@@ -1963,8 +1937,6 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
 
 #endif /* !CONFIG_NUMA_BALANCING */
 
-#ifdef CONFIG_SMP
-
 static inline void
 queue_balance_callback(struct rq *rq,
 		       struct balance_callback *head,
@@ -2130,8 +2102,6 @@ static inline const struct cpumask *task_user_cpus(struct task_struct *p)
 	return p->user_cpus_ptr;
 }
 
-#endif /* CONFIG_SMP */
-
 #ifdef CONFIG_CGROUP_SCHED
 
 /*
@@ -2418,7 +2388,6 @@ struct sched_class {
 	void (*put_prev_task)(struct rq *rq, struct task_struct *p, struct task_struct *next);
 	void (*set_next_task)(struct rq *rq, struct task_struct *p, bool first);
 
-#ifdef CONFIG_SMP
 	int  (*select_task_rq)(struct task_struct *p, int task_cpu, int flags);
 
 	void (*migrate_task_rq)(struct task_struct *p, int new_cpu);
@@ -2431,7 +2400,6 @@ struct sched_class {
 	void (*rq_offline)(struct rq *rq);
 
 	struct rq *(*find_lock_rq)(struct task_struct *p, struct rq *rq);
-#endif /* CONFIG_SMP */
 
 	void (*task_tick)(struct rq *rq, struct task_struct *p, int queued);
 	void (*task_fork)(struct task_struct *p);
@@ -2583,8 +2551,6 @@ extern struct task_struct *pick_task_idle(struct rq *rq);
 #define SCA_MIGRATE_ENABLE	0x04
 #define SCA_USER		0x08
 
-#ifdef CONFIG_SMP
-
 extern void update_group_capacity(struct sched_domain *sd, int cpu);
 
 extern void sched_balance_trigger(struct rq *rq);
@@ -2636,26 +2602,6 @@ static inline struct task_struct *get_push_task(struct rq *rq)
 
 extern int push_cpu_stop(void *arg);
 
-#else /* !CONFIG_SMP: */
-
-static inline bool task_allowed_on_cpu(struct task_struct *p, int cpu)
-{
-	return true;
-}
-
-static inline int __set_cpus_allowed_ptr(struct task_struct *p,
-					 struct affinity_context *ctx)
-{
-	return set_cpus_allowed_ptr(p, ctx->new_mask);
-}
-
-static inline cpumask_t *alloc_user_cpus_ptr(int node)
-{
-	return NULL;
-}
-
-#endif /* !CONFIG_SMP */
-
 #ifdef CONFIG_CPU_IDLE
 
 static inline void idle_set_state(struct rq *rq,
@@ -2932,8 +2878,6 @@ static inline class_##name##_t class_##name##_constructor(type *lock, type *lock
 { class_##name##_t _t = { .lock = lock, .lock2 = lock2 }, *_T = &_t;			\
   _lock; return _t; }
 
-#ifdef CONFIG_SMP
-
 static inline bool rq_order_less(struct rq *rq1, struct rq *rq2)
 {
 #ifdef CONFIG_SCHED_CORE
@@ -3093,42 +3037,6 @@ extern void set_rq_offline(struct rq *rq);
 
 extern bool sched_smp_initialized;
 
-#else /* !CONFIG_SMP: */
-
-/*
- * double_rq_lock - safely lock two runqueues
- *
- * Note this does not disable interrupts like task_rq_lock,
- * you need to do so manually before calling.
- */
-static inline void double_rq_lock(struct rq *rq1, struct rq *rq2)
-	__acquires(rq1->lock)
-	__acquires(rq2->lock)
-{
-	WARN_ON_ONCE(!irqs_disabled());
-	WARN_ON_ONCE(rq1 != rq2);
-	raw_spin_rq_lock(rq1);
-	__acquire(rq2->lock);	/* Fake it out ;) */
-	double_rq_clock_clear_update(rq1, rq2);
-}
-
-/*
- * double_rq_unlock - safely unlock two runqueues
- *
- * Note this does not restore interrupts like task_rq_unlock,
- * you need to do so manually after calling.
- */
-static inline void double_rq_unlock(struct rq *rq1, struct rq *rq2)
-	__releases(rq1->lock)
-	__releases(rq2->lock)
-{
-	WARN_ON_ONCE(rq1 != rq2);
-	raw_spin_rq_unlock(rq1);
-	__release(rq2->lock);
-}
-
-#endif /* !CONFIG_SMP */
-
 DEFINE_LOCK_GUARD_2(double_rq_lock, struct rq,
 		    double_rq_lock(_T->lock, _T->lock2),
 		    double_rq_unlock(_T->lock, _T->lock2))
@@ -3187,7 +3095,7 @@ extern void nohz_balance_exit_idle(struct rq *rq);
 static inline void nohz_balance_exit_idle(struct rq *rq) { }
 #endif /* !CONFIG_NO_HZ_COMMON */
 
-#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
+#ifdef CONFIG_NO_HZ_COMMON
 extern void nohz_run_idle_balance(int cpu);
 #else
 static inline void nohz_run_idle_balance(int cpu) { }
@@ -3313,8 +3221,6 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) { }
 # define arch_scale_freq_invariant()	false
 #endif
 
-#ifdef CONFIG_SMP
-
 unsigned long effective_cpu_util(int cpu, unsigned long util_cfs,
 				 unsigned long *min,
 				 unsigned long *max);
@@ -3358,10 +3264,6 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
 	return READ_ONCE(rq->avg_rt.util_avg);
 }
 
-#else /* !CONFIG_SMP: */
-static inline bool update_other_load_avgs(struct rq *rq) { return false; }
-#endif /* !CONFIG_SMP */
-
 #ifdef CONFIG_UCLAMP_TASK
 
 unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
@@ -3580,7 +3482,6 @@ static inline void membarrier_switch_mm(struct rq *rq,
 
 #endif /* !CONFIG_MEMBARRIER */
 
-#ifdef CONFIG_SMP
 static inline bool is_per_cpu_kthread(struct task_struct *p)
 {
 	if (!(p->flags & PF_KTHREAD))
@@ -3591,7 +3492,6 @@ static inline bool is_per_cpu_kthread(struct task_struct *p)
 
 	return true;
 }
-#endif /* CONFIG_SMP */
 
 extern void swake_up_all_locked(struct swait_queue_head *q);
 extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
@@ -3890,7 +3790,6 @@ static inline void init_sched_mm_cid(struct task_struct *t) { }
 
 extern u64 avg_vruntime(struct cfs_rq *cfs_rq);
 extern int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se);
-#ifdef CONFIG_SMP
 static inline
 void move_queued_task_locked(struct rq *src_rq, struct rq *dst_rq, struct task_struct *task)
 {
@@ -3911,7 +3810,6 @@ bool task_is_pushable(struct rq *rq, struct task_struct *p, int cpu)
 
 	return false;
 }
-#endif /* CONFIG_SMP */
 
 #ifdef CONFIG_RT_MUTEXES
 
@@ -3952,21 +3850,8 @@ extern void check_class_changed(struct rq *rq, struct task_struct *p,
 				const struct sched_class *prev_class,
 				int oldprio);
 
-#ifdef CONFIG_SMP
 extern struct balance_callback *splice_balance_callbacks(struct rq *rq);
 extern void balance_callbacks(struct rq *rq, struct balance_callback *head);
-#else /* !CONFIG_SMP: */
-
-static inline struct balance_callback *splice_balance_callbacks(struct rq *rq)
-{
-	return NULL;
-}
-
-static inline void balance_callbacks(struct rq *rq, struct balance_callback *head)
-{
-}
-
-#endif /* !CONFIG_SMP */
 
 #ifdef CONFIG_SCHED_CLASS_EXT
 /*