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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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dce48a84ad
Dimitri Sivanich noticed that xtime_lock is held write locked across calc_load() which iterates over all online CPUs. That can cause long latencies for xtime_lock readers on large SMP systems. The load average calculation is an rough estimate anyway so there is no real need to protect the readers vs. the update. It's not a problem when the avenrun array is updated while a reader copies the values. Instead of iterating over all online CPUs let the scheduler_tick code update the number of active tasks shortly before the avenrun update happens. The avenrun update itself is handled by the CPU which calls do_timer(). [ Impact: reduce xtime_lock write locked section ] Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra <peterz@infradead.org>
130 lines
3.0 KiB
C
130 lines
3.0 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, int sync)
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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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/* adjust the active tasks as we might go into a long sleep */
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calc_load_account_active(rq);
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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, 0);
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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, 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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static 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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.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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