1// SPDX-License-Identifier: GPL-2.0
 
  2/*
  3 * stop-task scheduling class.
  4 *
  5 * The stop task is the highest priority task in the system, it preempts
  6 * everything and will be preempted by nothing.
  7 *
  8 * See kernel/stop_machine.c
  9 */
 10
 11#ifdef CONFIG_SMP
 12static int
 13select_task_rq_stop(struct task_struct *p, int cpu, int flags)
 14{
 15	return task_cpu(p); /* stop tasks as never migrate */
 16}
 17
 18static int
 19balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 20{
 21	return sched_stop_runnable(rq);
 22}
 23#endif /* CONFIG_SMP */
 24
 25static void
 26check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
 27{
 28	/* we're never preempted */
 29}
 30
 31static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
 32{
 33	stop->se.exec_start = rq_clock_task(rq);
 34}
 35
 36static struct task_struct *pick_task_stop(struct rq *rq)
 37{
 38	if (!sched_stop_runnable(rq))
 39		return NULL;
 40
 41	return rq->stop;
 42}
 43
 44static struct task_struct *pick_next_task_stop(struct rq *rq)
 45{
 46	struct task_struct *p = pick_task_stop(rq);
 47
 48	if (p)
 49		set_next_task_stop(rq, p, true);
 50
 51	return p;
 52}
 53
 54static void
 55enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 56{
 57	add_nr_running(rq, 1);
 58}
 59
 60static void
 61dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 62{
 63	sub_nr_running(rq, 1);
 64}
 65
 66static void yield_task_stop(struct rq *rq)
 67{
 68	BUG(); /* the stop task should never yield, its pointless. */
 69}
 70
 71static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 72{
 73	struct task_struct *curr = rq->curr;
 74	u64 now, delta_exec;
 75
 76	now = rq_clock_task(rq);
 77	delta_exec = now - curr->se.exec_start;
 78	if (unlikely((s64)delta_exec < 0))
 79		delta_exec = 0;
 80
 81	schedstat_set(curr->stats.exec_max,
 82		      max(curr->stats.exec_max, delta_exec));
 83
 84	update_current_exec_runtime(curr, now, delta_exec);
 85}
 86
 87/*
 88 * scheduler tick hitting a task of our scheduling class.
 89 *
 90 * NOTE: This function can be called remotely by the tick offload that
 91 * goes along full dynticks. Therefore no local assumption can be made
 92 * and everything must be accessed through the @rq and @curr passed in
 93 * parameters.
 94 */
 95static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 96{
 97}
 98
 
 
 
 
 99static void switched_to_stop(struct rq *rq, struct task_struct *p)
100{
101	BUG(); /* its impossible to change to this class */
102}
103
104static void
105prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
106{
107	BUG(); /* how!?, what priority? */
108}
109
110static void update_curr_stop(struct rq *rq)
 
111{
 
112}
113
114/*
115 * Simple, special scheduling class for the per-CPU stop tasks:
116 */
117DEFINE_SCHED_CLASS(stop) = {
 
118
119	.enqueue_task		= enqueue_task_stop,
120	.dequeue_task		= dequeue_task_stop,
121	.yield_task		= yield_task_stop,
122
123	.check_preempt_curr	= check_preempt_curr_stop,
124
125	.pick_next_task		= pick_next_task_stop,
126	.put_prev_task		= put_prev_task_stop,
127	.set_next_task          = set_next_task_stop,
128
129#ifdef CONFIG_SMP
130	.balance		= balance_stop,
131	.pick_task		= pick_task_stop,
132	.select_task_rq		= select_task_rq_stop,
133	.set_cpus_allowed	= set_cpus_allowed_common,
134#endif
135
 
136	.task_tick		= task_tick_stop,
137
 
 
138	.prio_changed		= prio_changed_stop,
139	.switched_to		= switched_to_stop,
140	.update_curr		= update_curr_stop,
141};

  1#include "sched.h"
  2
  3/*
  4 * stop-task scheduling class.
  5 *
  6 * The stop task is the highest priority task in the system, it preempts
  7 * everything and will be preempted by nothing.
  8 *
  9 * See kernel/stop_machine.c
 10 */
 11
 12#ifdef CONFIG_SMP
 13static int
 14select_task_rq_stop(struct task_struct *p, int sd_flag, int flags)
 15{
 16	return task_cpu(p); /* stop tasks as never migrate */
 17}
 
 
 
 
 
 
 18#endif /* CONFIG_SMP */
 19
 20static void
 21check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
 22{
 23	/* we're never preempted */
 24}
 25
 
 
 
 
 
 
 
 
 
 
 
 
 
 26static struct task_struct *pick_next_task_stop(struct rq *rq)
 27{
 28	struct task_struct *stop = rq->stop;
 29
 30	if (stop && stop->on_rq)
 31		return stop;
 32
 33	return NULL;
 34}
 35
 36static void
 37enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 38{
 39	inc_nr_running(rq);
 40}
 41
 42static void
 43dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 44{
 45	dec_nr_running(rq);
 46}
 47
 48static void yield_task_stop(struct rq *rq)
 49{
 50	BUG(); /* the stop task should never yield, its pointless. */
 51}
 52
 53static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 54{
 
 
 
 
 
 
 
 
 
 
 
 
 55}
 56
 
 
 
 
 
 
 
 
 57static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 58{
 59}
 60
 61static void set_curr_task_stop(struct rq *rq)
 62{
 63}
 64
 65static void switched_to_stop(struct rq *rq, struct task_struct *p)
 66{
 67	BUG(); /* its impossible to change to this class */
 68}
 69
 70static void
 71prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 72{
 73	BUG(); /* how!?, what priority? */
 74}
 75
 76static unsigned int
 77get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 78{
 79	return 0;
 80}
 81
 82/*
 83 * Simple, special scheduling class for the per-CPU stop tasks:
 84 */
 85const struct sched_class stop_sched_class = {
 86	.next			= &rt_sched_class,
 87
 88	.enqueue_task		= enqueue_task_stop,
 89	.dequeue_task		= dequeue_task_stop,
 90	.yield_task		= yield_task_stop,
 91
 92	.check_preempt_curr	= check_preempt_curr_stop,
 93
 94	.pick_next_task		= pick_next_task_stop,
 95	.put_prev_task		= put_prev_task_stop,
 
 96
 97#ifdef CONFIG_SMP
 
 
 98	.select_task_rq		= select_task_rq_stop,
 
 99#endif
100
101	.set_curr_task          = set_curr_task_stop,
102	.task_tick		= task_tick_stop,
103
104	.get_rr_interval	= get_rr_interval_stop,
105
106	.prio_changed		= prio_changed_stop,
107	.switched_to		= switched_to_stop,
 
108};