// SPDX-License-Identifier: GPL-2.0
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/*
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* stop-task scheduling class.
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*
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* The stop task is the highest priority task in the system, it preempts
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* everything and will be preempted by nothing.
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*
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* See kernel/stop_machine.c
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*/
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#include "sched.h"
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#ifdef CONFIG_SMP
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static int
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select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags,
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int sibling_count_hint)
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{
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return task_cpu(p); /* stop tasks as never migrate */
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}
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#endif /* CONFIG_SMP */
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static void
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check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
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{
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/* we're never preempted */
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}
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static struct task_struct *
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pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
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{
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struct task_struct *stop = rq->stop;
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if (!stop || !task_on_rq_queued(stop))
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return NULL;
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put_prev_task(rq, prev);
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stop->se.exec_start = rq_clock_task(rq);
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return stop;
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}
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static void
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enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
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{
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add_nr_running(rq, 1);
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}
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static void
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dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
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{
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sub_nr_running(rq, 1);
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}
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static void yield_task_stop(struct rq *rq)
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{
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BUG(); /* the stop task should never yield, its pointless. */
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}
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static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
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{
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struct task_struct *curr = rq->curr;
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u64 delta_exec;
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delta_exec = rq_clock_task(rq) - curr->se.exec_start;
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if (unlikely((s64)delta_exec < 0))
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delta_exec = 0;
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schedstat_set(curr->se.statistics.exec_max,
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max(curr->se.statistics.exec_max, delta_exec));
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curr->se.sum_exec_runtime += delta_exec;
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account_group_exec_runtime(curr, delta_exec);
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curr->se.exec_start = rq_clock_task(rq);
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cgroup_account_cputime(curr, delta_exec);
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}
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/*
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* scheduler tick hitting a task of our scheduling class.
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*
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* NOTE: This function can be called remotely by the tick offload that
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* goes along full dynticks. Therefore no local assumption can be made
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* and everything must be accessed through the @rq and @curr passed in
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* parameters.
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*/
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static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
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{
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}
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static void set_curr_task_stop(struct rq *rq)
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{
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struct task_struct *stop = rq->stop;
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stop->se.exec_start = rq_clock_task(rq);
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}
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static void switched_to_stop(struct rq *rq, struct task_struct *p)
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{
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BUG(); /* its impossible to change to this class */
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}
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static void
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prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
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{
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BUG(); /* how!?, what priority? */
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}
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static unsigned int
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get_rr_interval_stop(struct rq *rq, struct task_struct *task)
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{
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return 0;
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}
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static void update_curr_stop(struct rq *rq)
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{
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}
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/*
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* Simple, special scheduling class for the per-CPU stop tasks:
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*/
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const struct sched_class stop_sched_class = {
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.next = &dl_sched_class,
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.enqueue_task = enqueue_task_stop,
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.dequeue_task = dequeue_task_stop,
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.yield_task = yield_task_stop,
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.check_preempt_curr = check_preempt_curr_stop,
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.pick_next_task = pick_next_task_stop,
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.put_prev_task = put_prev_task_stop,
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#ifdef CONFIG_SMP
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.select_task_rq = select_task_rq_stop,
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.set_cpus_allowed = set_cpus_allowed_common,
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#endif
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.set_curr_task = set_curr_task_stop,
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.task_tick = task_tick_stop,
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.get_rr_interval = get_rr_interval_stop,
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.prio_changed = prio_changed_stop,
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.switched_to = switched_to_stop,
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.update_curr = update_curr_stop,
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};
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