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
 26wakeup_preempt_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	update_curr_common(rq);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 74}
 75
 76/*
 77 * scheduler tick hitting a task of our scheduling class.
 78 *
 79 * NOTE: This function can be called remotely by the tick offload that
 80 * goes along full dynticks. Therefore no local assumption can be made
 81 * and everything must be accessed through the @rq and @curr passed in
 82 * parameters.
 83 */
 84static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 85{
 86}
 87
 88static void switched_to_stop(struct rq *rq, struct task_struct *p)
 89{
 90	BUG(); /* its impossible to change to this class */
 91}
 92
 93static void
 94prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 95{
 96	BUG(); /* how!?, what priority? */
 97}
 98
 99static void update_curr_stop(struct rq *rq)
100{
101}
102
103/*
104 * Simple, special scheduling class for the per-CPU stop tasks:
105 */
106DEFINE_SCHED_CLASS(stop) = {
 
107
108	.enqueue_task		= enqueue_task_stop,
109	.dequeue_task		= dequeue_task_stop,
110	.yield_task		= yield_task_stop,
111
112	.wakeup_preempt		= wakeup_preempt_stop,
113
114	.pick_next_task		= pick_next_task_stop,
115	.put_prev_task		= put_prev_task_stop,
116	.set_next_task          = set_next_task_stop,
117
118#ifdef CONFIG_SMP
119	.balance		= balance_stop,
120	.pick_task		= pick_task_stop,
121	.select_task_rq		= select_task_rq_stop,
122	.set_cpus_allowed	= set_cpus_allowed_common,
123#endif
124
125	.task_tick		= task_tick_stop,
126
127	.prio_changed		= prio_changed_stop,
128	.switched_to		= switched_to_stop,
129	.update_curr		= update_curr_stop,
130};

  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#include "sched.h"
 11
 12#ifdef CONFIG_SMP
 13static int
 14select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags)
 15{
 16	return task_cpu(p); /* stop tasks as never migrate */
 17}
 18
 19static int
 20balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 21{
 22	return sched_stop_runnable(rq);
 23}
 24#endif /* CONFIG_SMP */
 25
 26static void
 27check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
 28{
 29	/* we're never preempted */
 30}
 31
 32static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
 33{
 34	stop->se.exec_start = rq_clock_task(rq);
 35}
 36
 37static struct task_struct *pick_next_task_stop(struct rq *rq)
 38{
 39	if (!sched_stop_runnable(rq))
 40		return NULL;
 41
 42	set_next_task_stop(rq, rq->stop, true);
 43	return rq->stop;
 44}
 45
 
 
 
 
 
 
 
 
 
 
 46static void
 47enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 48{
 49	add_nr_running(rq, 1);
 50}
 51
 52static void
 53dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 54{
 55	sub_nr_running(rq, 1);
 56}
 57
 58static void yield_task_stop(struct rq *rq)
 59{
 60	BUG(); /* the stop task should never yield, its pointless. */
 61}
 62
 63static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 64{
 65	struct task_struct *curr = rq->curr;
 66	u64 delta_exec;
 67
 68	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
 69	if (unlikely((s64)delta_exec < 0))
 70		delta_exec = 0;
 71
 72	schedstat_set(curr->se.statistics.exec_max,
 73			max(curr->se.statistics.exec_max, delta_exec));
 74
 75	curr->se.sum_exec_runtime += delta_exec;
 76	account_group_exec_runtime(curr, delta_exec);
 77
 78	curr->se.exec_start = rq_clock_task(rq);
 79	cgroup_account_cputime(curr, delta_exec);
 80}
 81
 82/*
 83 * scheduler tick hitting a task of our scheduling class.
 84 *
 85 * NOTE: This function can be called remotely by the tick offload that
 86 * goes along full dynticks. Therefore no local assumption can be made
 87 * and everything must be accessed through the @rq and @curr passed in
 88 * parameters.
 89 */
 90static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 91{
 92}
 93
 94static void switched_to_stop(struct rq *rq, struct task_struct *p)
 95{
 96	BUG(); /* its impossible to change to this class */
 97}
 98
 99static void
100prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
101{
102	BUG(); /* how!?, what priority? */
103}
104
105static void update_curr_stop(struct rq *rq)
106{
107}
108
109/*
110 * Simple, special scheduling class for the per-CPU stop tasks:
111 */
112const struct sched_class stop_sched_class
113	__attribute__((section("__stop_sched_class"))) = {
114
115	.enqueue_task		= enqueue_task_stop,
116	.dequeue_task		= dequeue_task_stop,
117	.yield_task		= yield_task_stop,
118
119	.check_preempt_curr	= check_preempt_curr_stop,
120
121	.pick_next_task		= pick_next_task_stop,
122	.put_prev_task		= put_prev_task_stop,
123	.set_next_task          = set_next_task_stop,
124
125#ifdef CONFIG_SMP
126	.balance		= balance_stop,
 
127	.select_task_rq		= select_task_rq_stop,
128	.set_cpus_allowed	= set_cpus_allowed_common,
129#endif
130
131	.task_tick		= task_tick_stop,
132
133	.prio_changed		= prio_changed_stop,
134	.switched_to		= switched_to_stop,
135	.update_curr		= update_curr_stop,
136};