5167e8d541
Thanks to Charles Wang for spotting the defects in the current code: - If we go idle during the sample window -- after sampling, we get a negative bias because we can negate our own sample. - If we wake up during the sample window we get a positive bias because we push the sample to a known active period. So rewrite the entire nohz load-avg muck once again, now adding copious documentation to the code. Reported-and-tested-by: Doug Smythies <dsmythies@telus.net> Reported-and-tested-by: Charles Wang <muming.wq@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: stable@kernel.org Link: http://lkml.kernel.org/r/1340373782.18025.74.camel@twins [ minor edits ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
99 lines
2.1 KiB
C
99 lines
2.1 KiB
C
#include "sched.h"
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/*
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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
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select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
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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, int flags)
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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 flags)
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{
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raw_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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raw_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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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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{
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BUG();
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}
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static void
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prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
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{
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BUG();
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}
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static unsigned int get_rr_interval_idle(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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/*
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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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.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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.select_task_rq = select_task_rq_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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.get_rr_interval = get_rr_interval_idle,
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.prio_changed = prio_changed_idle,
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.switched_to = switched_to_idle,
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};
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