b2d70222db
In order to tell the previous sched_class what the next task is, add
put_prev_task(.next).
Notable SCX will use this to:
1) determine the next task will leave the SCX sched class and push
the current task to another CPU if possible.
2) statistics on how often and which other classes preempt it
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20240813224016.367421076@infradead.org
120 lines
2.6 KiB
C
120 lines
2.6 KiB
C
// 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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#ifdef CONFIG_SMP
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static int
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select_task_rq_stop(struct task_struct *p, int cpu, int flags)
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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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static int
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balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
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{
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return sched_stop_runnable(rq);
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}
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#endif /* CONFIG_SMP */
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static void
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wakeup_preempt_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 void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
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{
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stop->se.exec_start = rq_clock_task(rq);
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}
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static struct task_struct *pick_task_stop(struct rq *rq)
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{
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if (!sched_stop_runnable(rq))
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return NULL;
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return rq->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 bool
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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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return true;
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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, struct task_struct *next)
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{
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update_curr_common(rq);
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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 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 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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DEFINE_SCHED_CLASS(stop) = {
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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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.wakeup_preempt = wakeup_preempt_stop,
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.pick_task = pick_task_stop,
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.put_prev_task = put_prev_task_stop,
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.set_next_task = set_next_task_stop,
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#ifdef CONFIG_SMP
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.balance = balance_stop,
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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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.task_tick = task_tick_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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