kernel/sched/stop_task.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * stop-task scheduling class.
0004  *
0005  * The stop task is the highest priority task in the system, it preempts
0006  * everything and will be preempted by nothing.
0007  *
0008  * See kernel/stop_machine.c
0009  */
0010
0011 #ifdef CONFIG_SMP
0012 static int
0013 select_task_rq_stop(struct task_struct *p, int cpu, int flags)
0014 {
0015     return task_cpu(p); /* stop tasks as never migrate */
0016 }
0017
0018 static int
0019 balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
0020 {
0021     return sched_stop_runnable(rq);
0022 }
0023 #endif /* CONFIG_SMP */
0024
0025 static void
0026 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
0027 {
0028     /* we're never preempted */
0029 }
0030
0031 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
0032 {
0033     stop->se.exec_start = rq_clock_task(rq);
0034 }
0035
0036 static struct task_struct *pick_task_stop(struct rq *rq)
0037 {
0038     if (!sched_stop_runnable(rq))
0039         return NULL;
0040
0041     return rq->stop;
0042 }
0043
0044 static struct task_struct *pick_next_task_stop(struct rq *rq)
0045 {
0046     struct task_struct *p = pick_task_stop(rq);
0047
0048     if (p)
0049         set_next_task_stop(rq, p, true);
0050
0051     return p;
0052 }
0053
0054 static void
0055 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
0056 {
0057     add_nr_running(rq, 1);
0058 }
0059
0060 static void
0061 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
0062 {
0063     sub_nr_running(rq, 1);
0064 }
0065
0066 static void yield_task_stop(struct rq *rq)
0067 {
0068     BUG(); /* the stop task should never yield, its pointless. */
0069 }
0070
0071 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
0072 {
0073     struct task_struct *curr = rq->curr;
0074     u64 delta_exec;
0075
0076     delta_exec = rq_clock_task(rq) - curr->se.exec_start;
0077     if (unlikely((s64)delta_exec < 0))
0078         delta_exec = 0;
0079
0080     schedstat_set(curr->stats.exec_max,
0081               max(curr->stats.exec_max, delta_exec));
0082
0083     curr->se.sum_exec_runtime += delta_exec;
0084     account_group_exec_runtime(curr, delta_exec);
0085
0086     curr->se.exec_start = rq_clock_task(rq);
0087     cgroup_account_cputime(curr, delta_exec);
0088 }
0089
0090 /*
0091  * scheduler tick hitting a task of our scheduling class.
0092  *
0093  * NOTE: This function can be called remotely by the tick offload that
0094  * goes along full dynticks. Therefore no local assumption can be made
0095  * and everything must be accessed through the @rq and @curr passed in
0096  * parameters.
0097  */
0098 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
0099 {
0100 }
0101
0102 static void switched_to_stop(struct rq *rq, struct task_struct *p)
0103 {
0104     BUG(); /* its impossible to change to this class */
0105 }
0106
0107 static void
0108 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
0109 {
0110     BUG(); /* how!?, what priority? */
0111 }
0112
0113 static void update_curr_stop(struct rq *rq)
0114 {
0115 }
0116
0117 /*
0118  * Simple, special scheduling class for the per-CPU stop tasks:
0119  */
0120 DEFINE_SCHED_CLASS(stop) = {
0121
0122     .enqueue_task       = enqueue_task_stop,
0123     .dequeue_task       = dequeue_task_stop,
0124     .yield_task     = yield_task_stop,
0125
0126     .check_preempt_curr = check_preempt_curr_stop,
0127
0128     .pick_next_task     = pick_next_task_stop,
0129     .put_prev_task      = put_prev_task_stop,
0130     .set_next_task          = set_next_task_stop,
0131
0132 #ifdef CONFIG_SMP
0133     .balance        = balance_stop,
0134     .pick_task      = pick_task_stop,
0135     .select_task_rq     = select_task_rq_stop,
0136     .set_cpus_allowed   = set_cpus_allowed_common,
0137 #endif
0138
0139     .task_tick      = task_tick_stop,
0140
0141     .prio_changed       = prio_changed_stop,
0142     .switched_to        = switched_to_stop,
0143     .update_curr        = update_curr_stop,
0144 };