sched/syscalls: Split out kernel/sched/syscalls.c from kernel/sched/core.c

core.c has become rather large, move most scheduler syscall
related functionality into a separate file, syscalls.c.

This is about ~15% of core.c's raw linecount.

Move the alloc_user_cpus_ptr(), __rt_effective_prio(),
rt_effective_prio(), uclamp_none(), uclamp_se_set()
and uclamp_bucket_id() inlines to kernel/sched/sched.h.

Internally export the __sched_setscheduler(), __sched_setaffinity(),
__setscheduler_prio(), set_load_weight(), enqueue_task(), dequeue_task(),
check_class_changed(), splice_balance_callbacks() and balance_callbacks()
methods to better facilitate this.

Move the new file's build to sched_policy.c, because it fits there
semantically, but also because it's the smallest of the 4 build units
under an allmodconfig build:

  -rw-rw-r-- 1 mingo mingo 7.3M May 27 12:35 kernel/sched/core.i
  -rw-rw-r-- 1 mingo mingo 6.4M May 27 12:36 kernel/sched/build_utility.i
  -rw-rw-r-- 1 mingo mingo 6.3M May 27 12:36 kernel/sched/fair.i
  -rw-rw-r-- 1 mingo mingo 5.8M May 27 12:36 kernel/sched/build_policy.i

This better balances build time for scheduler subsystem rebuilds.

I build-tested this new file as a standalone syscalls.o file for a bit,
to make sure all the encapsulations & abstractions are robust.

Also update/add my copyright notices to these files.

Build time measurements:

 # -Before/+After:

 kepler:~/tip> perf stat -e 'cycles,instructions,duration_time' --sync --repeat 5 --pre 'rm -f kernel/sched/*.o' m kernel/sched/built-in.a >/dev/null

 Performance counter stats for 'm kernel/sched/built-in.a' (5 runs):

 -    71,938,508,607      cycles                                                                  ( +-  0.17% )
 +    71,992,916,493      cycles                                                                  ( +-  0.22% )
 -   106,214,780,964      instructions                     #    1.48  insn per cycle              ( +-  0.01% )
 +   105,450,231,154      instructions                     #    1.46  insn per cycle              ( +-  0.01% )
 -     5,878,232,620 ns   duration_time                                                           ( +-  0.38% )
 +     5,290,085,069 ns   duration_time                                                           ( +-  0.21% )

 -            5.8782 +- 0.0221 seconds time elapsed  ( +-  0.38% )
 +            5.2901 +- 0.0111 seconds time elapsed  ( +-  0.21% )

Build time improvement of -11.1% (duration_time) is expected: the
parallel build time of the scheduler subsystem is determined by the
largest, slowest to build object file, which is kernel/sched/core.o.
By moving ~15% of its complexity into another build unit, we reduced
build time by -11%.

Measured cycles spent on building is within its ~0.2% stddev noise envelope.

The -0.7% reduction in instructions spent on building the scheduler is
statistically reliable and somewhat surprising - I can only speculate:
maybe compilers aren't that efficient at building & optimizing 10+ KLOC files
(core.c), and it's an overall win to balance the linecount a bit.

Anyway, this might be a data point that suggests that reducing the linecount
of our largest files will improve not just code readability and maintainability,
but might also improve build times a bit.

Code generation got a bit worse, by 0.5kb text on an x86 defconfig build:

  # -Before/+After:

  kepler:~/tip> size vmlinux
     text	   data	    bss	    dec	    hex	filename
  -26475475	10439178	1740804	38655457	24dd5e1	vmlinux
  +26476003	10439178	1740804	38655985	24dd7f1	vmlinux

  kepler:~/tip> size kernel/sched/built-in.a
     text	   data	    bss	    dec	    hex	filename
  - 76056	  30025	    489	 106570	  1a04a	kernel/sched/core.o (ex kernel/sched/built-in.a)
  + 63452	  29453	    489	  93394	  16cd2	kernel/sched/core.o (ex kernel/sched/built-in.a)
    44299	   2181	    104	  46584	   b5f8	kernel/sched/fair.o (ex kernel/sched/built-in.a)
  - 42764	   3424	    120	  46308	   b4e4	kernel/sched/build_policy.o (ex kernel/sched/built-in.a)
  + 55651	   4044	    120	  59815	   e9a7	kernel/sched/build_policy.o (ex kernel/sched/built-in.a)
    44866	  12655	   2192	  59713	   e941	kernel/sched/build_utility.o (ex kernel/sched/built-in.a)
    44866	  12655	   2192	  59713	   e941	kernel/sched/build_utility.o (ex kernel/sched/built-in.a)

This is primarily due to the extra functions exported, and the size
gets exaggerated somewhat by __pfx CFI function padding:

	ffffffff810cc710 <__pfx_enqueue_task>:
	ffffffff810cc710:	90                   	nop
	ffffffff810cc711:	90                   	nop
	ffffffff810cc712:	90                   	nop
	ffffffff810cc713:	90                   	nop
	ffffffff810cc714:	90                   	nop
	ffffffff810cc715:	90                   	nop
	ffffffff810cc716:	90                   	nop
	ffffffff810cc717:	90                   	nop
	ffffffff810cc718:	90                   	nop
	ffffffff810cc719:	90                   	nop
	ffffffff810cc71a:	90                   	nop
	ffffffff810cc71b:	90                   	nop
	ffffffff810cc71c:	90                   	nop
	ffffffff810cc71d:	90                   	nop
	ffffffff810cc71e:	90                   	nop
	ffffffff810cc71f:	90                   	nop

AFAICS the cost is primarily not to core.o and fair.o though (which contain
most performance sensitive scheduler functions), only to syscalls.o
that get called with much lower frequency - so I think this is an acceptable
trade-off for better code separation.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Link: https://lore.kernel.org/r/20240407084319.1462211-2-mingo@kernel.org

kernel/sched/build_policy.c

@@ -52,3 +52,4 @@
 #include "cputime.c"
 #include "deadline.c"
 
+#include "syscalls.c"

kernel/sched/sched.h

@@ -2402,8 +2402,19 @@ extern void update_group_capacity(struct sched_domain *sd, int cpu);
 
 extern void sched_balance_trigger(struct rq *rq);
 
+extern int __set_cpus_allowed_ptr(struct task_struct *p, struct affinity_context *ctx);
 extern void set_cpus_allowed_common(struct task_struct *p, struct affinity_context *ctx);
 
+static inline cpumask_t *alloc_user_cpus_ptr(int node)
+{
+	/*
+	 * See do_set_cpus_allowed() above for the rcu_head usage.
+	 */
+	int size = max_t(int, cpumask_size(), sizeof(struct rcu_head));
+
+	return kmalloc_node(size, GFP_KERNEL, node);
+}
+
 static inline struct task_struct *get_push_task(struct rq *rq)
 {
 	struct task_struct *p = rq->curr;
@@ -2425,7 +2436,20 @@ static inline struct task_struct *get_push_task(struct rq *rq)
 
 extern int push_cpu_stop(void *arg);
 
-#endif
+#else /* !CONFIG_SMP: */
+
+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,
@@ -3097,6 +3121,36 @@ static inline bool uclamp_is_used(void)
 {
 	return static_branch_likely(&sched_uclamp_used);
 }
+
+#define for_each_clamp_id(clamp_id) \
+	for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++)
+
+extern unsigned int sysctl_sched_uclamp_util_min_rt_default;
+
+
+static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
+{
+	if (clamp_id == UCLAMP_MIN)
+		return 0;
+	return SCHED_CAPACITY_SCALE;
+}
+
+/* Integer rounded range for each bucket */
+#define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)
+
+static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
+{
+	return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
+}
+
+static inline void uclamp_se_set(struct uclamp_se *uc_se,
+				 unsigned int value, bool user_defined)
+{
+	uc_se->value = value;
+	uc_se->bucket_id = uclamp_bucket_id(value);
+	uc_se->user_defined = user_defined;
+}
+
 #else /* CONFIG_UCLAMP_TASK */
 static inline unsigned long uclamp_eff_value(struct task_struct *p,
 					     enum uclamp_id clamp_id)
@@ -3132,6 +3186,7 @@ static inline bool uclamp_rq_is_idle(struct rq *rq)
 {
 	return false;
 }
+
 #endif /* CONFIG_UCLAMP_TASK */
 
 #ifdef CONFIG_HAVE_SCHED_AVG_IRQ
@@ -3480,4 +3535,53 @@ 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_RT_MUTEXES
+static inline int __rt_effective_prio(struct task_struct *pi_task, int prio)
+{
+	if (pi_task)
+		prio = min(prio, pi_task->prio);
+
+	return prio;
+}
+
+static inline int rt_effective_prio(struct task_struct *p, int prio)
+{
+	struct task_struct *pi_task = rt_mutex_get_top_task(p);
+
+	return __rt_effective_prio(pi_task, prio);
+}
+#else
+static inline int rt_effective_prio(struct task_struct *p, int prio)
+{
+	return prio;
+}
+#endif
+
+extern int __sched_setscheduler(struct task_struct *p, const struct sched_attr *attr, bool user, bool pi);
+extern int __sched_setaffinity(struct task_struct *p, struct affinity_context *ctx);
+extern void __setscheduler_prio(struct task_struct *p, int prio);
+extern void set_load_weight(struct task_struct *p, bool update_load);
+extern void enqueue_task(struct rq *rq, struct task_struct *p, int flags);
+extern void dequeue_task(struct rq *rq, struct task_struct *p, int flags);
+
+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
+
+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
+
 #endif /* _KERNEL_SCHED_SCHED_H */