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8f4d37ec07
Use HR-timers (when available) to deliver an accurate preemption tick. The regular scheduler tick that runs at 1/HZ can be too coarse when nice level are used. The fairness system will still keep the cpu utilisation 'fair' by then delaying the task that got an excessive amount of CPU time but try to minimize this by delivering preemption points spot-on. The average frequency of this extra interrupt is sched_latency / nr_latency. Which need not be higher than 1/HZ, its just that the distribution within the sched_latency period is important. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
130 lines
2.9 KiB
C
130 lines
2.9 KiB
C
/*
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* idle-task scheduling class.
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*
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* (NOTE: these are not related to SCHED_IDLE tasks which are
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* handled in sched_fair.c)
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*/
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#ifdef CONFIG_SMP
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static int select_task_rq_idle(struct task_struct *p, int sync)
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{
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return task_cpu(p); /* IDLE tasks as never migrated */
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}
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#endif /* CONFIG_SMP */
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/*
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* Idle tasks are unconditionally rescheduled:
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*/
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static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p)
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{
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resched_task(rq->idle);
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}
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static struct task_struct *pick_next_task_idle(struct rq *rq)
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{
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schedstat_inc(rq, sched_goidle);
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return rq->idle;
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}
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/*
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* It is not legal to sleep in the idle task - print a warning
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* message if some code attempts to do it:
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*/
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static void
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dequeue_task_idle(struct rq *rq, struct task_struct *p, int sleep)
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{
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spin_unlock_irq(&rq->lock);
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printk(KERN_ERR "bad: scheduling from the idle thread!\n");
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dump_stack();
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spin_lock_irq(&rq->lock);
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}
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static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
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{
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}
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#ifdef CONFIG_SMP
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static unsigned long
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load_balance_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
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unsigned long max_load_move,
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struct sched_domain *sd, enum cpu_idle_type idle,
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int *all_pinned, int *this_best_prio)
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{
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return 0;
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}
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static int
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move_one_task_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
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struct sched_domain *sd, enum cpu_idle_type idle)
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{
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return 0;
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}
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#endif
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static void task_tick_idle(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_idle(struct rq *rq)
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{
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}
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static void switched_to_idle(struct rq *rq, struct task_struct *p,
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int running)
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{
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/* Can this actually happen?? */
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if (running)
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resched_task(rq->curr);
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else
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check_preempt_curr(rq, p);
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}
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static void prio_changed_idle(struct rq *rq, struct task_struct *p,
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int oldprio, int running)
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{
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/* This can happen for hot plug CPUS */
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/*
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* Reschedule if we are currently running on this runqueue and
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* our priority decreased, or if we are not currently running on
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* this runqueue and our priority is higher than the current's
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*/
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if (running) {
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if (p->prio > oldprio)
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resched_task(rq->curr);
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} else
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check_preempt_curr(rq, p);
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}
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/*
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* Simple, special scheduling class for the per-CPU idle tasks:
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*/
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const struct sched_class idle_sched_class = {
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/* .next is NULL */
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/* no enqueue/yield_task for idle tasks */
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/* dequeue is not valid, we print a debug message there: */
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.dequeue_task = dequeue_task_idle,
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#ifdef CONFIG_SMP
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.select_task_rq = select_task_rq_idle,
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#endif /* CONFIG_SMP */
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.check_preempt_curr = check_preempt_curr_idle,
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.pick_next_task = pick_next_task_idle,
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.put_prev_task = put_prev_task_idle,
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#ifdef CONFIG_SMP
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.load_balance = load_balance_idle,
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.move_one_task = move_one_task_idle,
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#endif
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.set_curr_task = set_curr_task_idle,
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.task_tick = task_tick_idle,
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.prio_changed = prio_changed_idle,
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.switched_to = switched_to_idle,
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/* no .task_new for idle tasks */
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};
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