Re: [PATCH 04/14] sched: SCHED_DEADLINE SMP-related data structures& logic.
From: Juri Lelli
Date: Thu Nov 21 2013 - 11:17:05 EST
On 11/21/2013 05:08 PM, Paul E. McKenney wrote:
> On Thu, Nov 21, 2013 at 03:13:28PM +0100, Juri Lelli wrote:
>> On 11/20/2013 07:51 PM, Steven Rostedt wrote:
>>> On Thu, 7 Nov 2013 14:43:38 +0100
>>> Juri Lelli <juri.lelli@xxxxxxxxx> wrote:
>>>
>>>
>>>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>>>> index cb93f2e..18a73b4 100644
>>>> --- a/kernel/sched/deadline.c
>>>> +++ b/kernel/sched/deadline.c
>>>> @@ -10,6 +10,7 @@
>>>> * miss some of their deadlines), and won't affect any other task.
>>>> *
>>>> * Copyright (C) 2012 Dario Faggioli <raistlin@xxxxxxxx>,
>>>> + * Juri Lelli <juri.lelli@xxxxxxxxx>,
>>>> * Michael Trimarchi <michael@xxxxxxxxxxxxxxxxxxxx>,
>>>> * Fabio Checconi <fchecconi@xxxxxxxxx>
>>>> */
>>>> @@ -20,6 +21,15 @@ static inline int dl_time_before(u64 a, u64 b)
>>>> return (s64)(a - b) < 0;
>>>> }
>>>>
>>>> +/*
>>>> + * Tells if entity @a should preempt entity @b.
>>>> + */
>>>> +static inline
>>>> +int dl_entity_preempt(struct sched_dl_entity *a, struct sched_dl_entity *b)
>>>> +{
>>>> + return dl_time_before(a->deadline, b->deadline);
>>>> +}
>>>> +
>>>> static inline struct task_struct *dl_task_of(struct sched_dl_entity *dl_se)
>>>> {
>>>> return container_of(dl_se, struct task_struct, dl);
>>>> @@ -53,8 +63,168 @@ static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
>>>> void init_dl_rq(struct dl_rq *dl_rq, struct rq *rq)
>>>> {
>>>> dl_rq->rb_root = RB_ROOT;
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> + /* zero means no -deadline tasks */
>>>
>>> I'm curious to why you add the '-' to -deadline.
>>>
>>
>> I guess "deadline tasks" is too much generic; "SCHED_DEADLINE tasks" too long;
>> "DL" or "-dl" can be associated to "download". Nothing special in the end, just
>> tought it was a reasonable abbreviation.
>
> My guess was that "-deadline" was an abbreviation for tasks that had
> missed their deadline, just so you know. ;-)
>
Argh! ;)
Actually, thinking about it twice: if we call "-rt tasks" things that are
governed by code that resides in sched/rt.c, we could agree on "-deadline
tasks" for things that pass through sched/deadline.c.
Thanks,
- Juri
>>>> + dl_rq->earliest_dl.curr = dl_rq->earliest_dl.next = 0;
>>>> +
>>>> + dl_rq->dl_nr_migratory = 0;
>>>> + dl_rq->overloaded = 0;
>>>> + dl_rq->pushable_dl_tasks_root = RB_ROOT;
>>>> +#endif
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> +
>>>> +static inline int dl_overloaded(struct rq *rq)
>>>> +{
>>>> + return atomic_read(&rq->rd->dlo_count);
>>>> +}
>>>> +
>>>> +static inline void dl_set_overload(struct rq *rq)
>>>> +{
>>>> + if (!rq->online)
>>>> + return;
>>>> +
>>>> + cpumask_set_cpu(rq->cpu, rq->rd->dlo_mask);
>>>> + /*
>>>> + * Must be visible before the overload count is
>>>> + * set (as in sched_rt.c).
>>>> + *
>>>> + * Matched by the barrier in pull_dl_task().
>>>> + */
>>>> + smp_wmb();
>>>> + atomic_inc(&rq->rd->dlo_count);
>>>> +}
>>>> +
>>>> +static inline void dl_clear_overload(struct rq *rq)
>>>> +{
>>>> + if (!rq->online)
>>>> + return;
>>>> +
>>>> + atomic_dec(&rq->rd->dlo_count);
>>>> + cpumask_clear_cpu(rq->cpu, rq->rd->dlo_mask);
>>>> +}
>>>> +
>>>> +static void update_dl_migration(struct dl_rq *dl_rq)
>>>> +{
>>>> + if (dl_rq->dl_nr_migratory && dl_rq->dl_nr_total > 1) {
>>>> + if (!dl_rq->overloaded) {
>>>> + dl_set_overload(rq_of_dl_rq(dl_rq));
>>>> + dl_rq->overloaded = 1;
>>>> + }
>>>> + } else if (dl_rq->overloaded) {
>>>> + dl_clear_overload(rq_of_dl_rq(dl_rq));
>>>> + dl_rq->overloaded = 0;
>>>> + }
>>>> +}
>>>> +
>>>> +static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>>> +{
>>>> + struct task_struct *p = dl_task_of(dl_se);
>>>> + dl_rq = &rq_of_dl_rq(dl_rq)->dl;
>>>> +
>>>> + dl_rq->dl_nr_total++;
>>>> + if (p->nr_cpus_allowed > 1)
>>>> + dl_rq->dl_nr_migratory++;
>>>> +
>>>> + update_dl_migration(dl_rq);
>>>> +}
>>>> +
>>>> +static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>>> +{
>>>> + struct task_struct *p = dl_task_of(dl_se);
>>>> + dl_rq = &rq_of_dl_rq(dl_rq)->dl;
>>>> +
>>>> + dl_rq->dl_nr_total--;
>>>> + if (p->nr_cpus_allowed > 1)
>>>> + dl_rq->dl_nr_migratory--;
>>>> +
>>>> + update_dl_migration(dl_rq);
>>>> +}
>>>> +
>>>> +/*
>>>> + * The list of pushable -deadline task is not a plist, like in
>>>> + * sched_rt.c, it is an rb-tree with tasks ordered by deadline.
>>>> + */
>>>> +static void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
>>>> +{
>>>> + struct dl_rq *dl_rq = &rq->dl;
>>>> + struct rb_node **link = &dl_rq->pushable_dl_tasks_root.rb_node;
>>>> + struct rb_node *parent = NULL;
>>>> + struct task_struct *entry;
>>>> + int leftmost = 1;
>>>> +
>>>> + BUG_ON(!RB_EMPTY_NODE(&p->pushable_dl_tasks));
>>>> +
>>>> + while (*link) {
>>>> + parent = *link;
>>>> + entry = rb_entry(parent, struct task_struct,
>>>> + pushable_dl_tasks);
>>>> + if (dl_entity_preempt(&p->dl, &entry->dl))
>>>> + link = &parent->rb_left;
>>>> + else {
>>>> + link = &parent->rb_right;
>>>> + leftmost = 0;
>>>> + }
>>>> + }
>>>> +
>>>> + if (leftmost)
>>>> + dl_rq->pushable_dl_tasks_leftmost = &p->pushable_dl_tasks;
>>>> +
>>>> + rb_link_node(&p->pushable_dl_tasks, parent, link);
>>>> + rb_insert_color(&p->pushable_dl_tasks, &dl_rq->pushable_dl_tasks_root);
>>>> +}
>>>> +
>>>> +static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
>>>> +{
>>>> + struct dl_rq *dl_rq = &rq->dl;
>>>> +
>>>> + if (RB_EMPTY_NODE(&p->pushable_dl_tasks))
>>>> + return;
>>>> +
>>>> + if (dl_rq->pushable_dl_tasks_leftmost == &p->pushable_dl_tasks) {
>>>> + struct rb_node *next_node;
>>>> +
>>>> + next_node = rb_next(&p->pushable_dl_tasks);
>>>> + dl_rq->pushable_dl_tasks_leftmost = next_node;
>>>> + }
>>>> +
>>>> + rb_erase(&p->pushable_dl_tasks, &dl_rq->pushable_dl_tasks_root);
>>>> + RB_CLEAR_NODE(&p->pushable_dl_tasks);
>>>> +}
>>>> +
>>>> +static inline int has_pushable_dl_tasks(struct rq *rq)
>>>> +{
>>>> + return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root);
>>>> +}
>>>> +
>>>> +static int push_dl_task(struct rq *rq);
>>>> +
>>>> +#else
>>>> +
>>>> +static inline
>>>> +void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
>>>> +{
>>>> +}
>>>> +
>>>> +static inline
>>>> +void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
>>>> +{
>>>> +}
>>>> +
>>>> +static inline
>>>> +void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>>> +{
>>>> +}
>>>> +
>>>> +static inline
>>>> +void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>>> +{
>>>> }
>>>>
>>>> +#endif /* CONFIG_SMP */
>>>> +
>>>> static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags);
>>>> static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags);
>>>> static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
>>>> @@ -307,6 +477,14 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
>>>> check_preempt_curr_dl(rq, p, 0);
>>>> else
>>>> resched_task(rq->curr);
>>>> +#ifdef CONFIG_SMP
>>>> + /*
>>>> + * Queueing this task back might have overloaded rq,
>>>> + * check if we need to kick someone away.
>>>> + */
>>>> + if (has_pushable_dl_tasks(rq))
>>>> + push_dl_task(rq);
>>>> +#endif
>>>> }
>>>> unlock:
>>>> raw_spin_unlock(&rq->lock);
>>>> @@ -397,6 +575,100 @@ static void update_curr_dl(struct rq *rq)
>>>> }
>>>> }
>>>>
>>>> +#ifdef CONFIG_SMP
>>>> +
>>>> +static struct task_struct *pick_next_earliest_dl_task(struct rq *rq, int cpu);
>>>> +
>>>> +static inline u64 next_deadline(struct rq *rq)
>>>> +{
>>>> + struct task_struct *next = pick_next_earliest_dl_task(rq, rq->cpu);
>>>> +
>>>> + if (next && dl_prio(next->prio))
>>>> + return next->dl.deadline;
>>>> + else
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
>>>> +{
>>>> + struct rq *rq = rq_of_dl_rq(dl_rq);
>>>> +
>>>> + if (dl_rq->earliest_dl.curr == 0 ||
>>>> + dl_time_before(deadline, dl_rq->earliest_dl.curr)) {
>>>> + /*
>>>> + * If the dl_rq had no -deadline tasks, or if the new task
>>>> + * has shorter deadline than the current one on dl_rq, we
>>>> + * know that the previous earliest becomes our next earliest,
>>>> + * as the new task becomes the earliest itself.
>>>> + */
>>>> + dl_rq->earliest_dl.next = dl_rq->earliest_dl.curr;
>>>> + dl_rq->earliest_dl.curr = deadline;
>>>> + } else if (dl_rq->earliest_dl.next == 0 ||
>>>> + dl_time_before(deadline, dl_rq->earliest_dl.next)) {
>>>> + /*
>>>> + * On the other hand, if the new -deadline task has a
>>>> + * a later deadline than the earliest one on dl_rq, but
>>>> + * it is earlier than the next (if any), we must
>>>> + * recompute the next-earliest.
>>>> + */
>>>> + dl_rq->earliest_dl.next = next_deadline(rq);
>>>> + }
>>>> +}
>>>> +
>>>> +static void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline)
>>>> +{
>>>> + struct rq *rq = rq_of_dl_rq(dl_rq);
>>>> +
>>>> + /*
>>>> + * Since we may have removed our earliest (and/or next earliest)
>>>> + * task we must recompute them.
>>>> + */
>>>> + if (!dl_rq->dl_nr_running) {
>>>> + dl_rq->earliest_dl.curr = 0;
>>>> + dl_rq->earliest_dl.next = 0;
>>>> + } else {
>>>> + struct rb_node *leftmost = dl_rq->rb_leftmost;
>>>> + struct sched_dl_entity *entry;
>>>> +
>>>> + entry = rb_entry(leftmost, struct sched_dl_entity, rb_node);
>>>> + dl_rq->earliest_dl.curr = entry->deadline;
>>>> + dl_rq->earliest_dl.next = next_deadline(rq);
>>>> + }
>>>> +}
>>>> +
>>>> +#else
>>>> +
>>>> +static inline void inc_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}
>>>> +static inline void dec_dl_deadline(struct dl_rq *dl_rq, u64 deadline) {}
>>>> +
>>>> +#endif /* CONFIG_SMP */
>>>> +
>>>> +static inline
>>>> +void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>>> +{
>>>> + int prio = dl_task_of(dl_se)->prio;
>>>> + u64 deadline = dl_se->deadline;
>>>> +
>>>> + WARN_ON(!dl_prio(prio));
>>>> + dl_rq->dl_nr_running++;
>>>> +
>>>> + inc_dl_deadline(dl_rq, deadline);
>>>> + inc_dl_migration(dl_se, dl_rq);
>>>> +}
>>>> +
>>>> +static inline
>>>> +void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
>>>> +{
>>>> + int prio = dl_task_of(dl_se)->prio;
>>>> +
>>>> + WARN_ON(!dl_prio(prio));
>>>> + WARN_ON(!dl_rq->dl_nr_running);
>>>> + dl_rq->dl_nr_running--;
>>>> +
>>>> + dec_dl_deadline(dl_rq, dl_se->deadline);
>>>> + dec_dl_migration(dl_se, dl_rq);
>>>> +}
>>>> +
>>>> static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
>>>> {
>>>> struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
>>>> @@ -424,7 +696,7 @@ static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
>>>> rb_link_node(&dl_se->rb_node, parent, link);
>>>> rb_insert_color(&dl_se->rb_node, &dl_rq->rb_root);
>>>>
>>>> - dl_rq->dl_nr_running++;
>>>> + inc_dl_tasks(dl_se, dl_rq);
>>>> }
>>>>
>>>> static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
>>>> @@ -444,7 +716,7 @@ static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
>>>> rb_erase(&dl_se->rb_node, &dl_rq->rb_root);
>>>> RB_CLEAR_NODE(&dl_se->rb_node);
>>>>
>>>> - dl_rq->dl_nr_running--;
>>>> + dec_dl_tasks(dl_se, dl_rq);
>>>> }
>>>>
>>>> static void
>>>> @@ -482,12 +754,17 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
>>>> return;
>>>>
>>>> enqueue_dl_entity(&p->dl, flags);
>>>> +
>>>> + if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
>>>> + enqueue_pushable_dl_task(rq, p);
>>>> +
>>>> inc_nr_running(rq);
>>>> }
>>>>
>>>> static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
>>>> {
>>>> dequeue_dl_entity(&p->dl);
>>>> + dequeue_pushable_dl_task(rq, p);
>>>> }
>>>>
>>>> static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
>>>> @@ -525,6 +802,77 @@ static void yield_task_dl(struct rq *rq)
>>>> update_curr_dl(rq);
>>>> }
>>>>
>>>> +#ifdef CONFIG_SMP
>>>> +
>>>> +static int find_later_rq(struct task_struct *task);
>>>> +static int latest_cpu_find(struct cpumask *span,
>>>> + struct task_struct *task,
>>>> + struct cpumask *later_mask);
>>>> +
>>>> +static int
>>>> +select_task_rq_dl(struct task_struct *p, int sd_flag, int flags)
>>>> +{
>>>> + struct task_struct *curr;
>>>> + struct rq *rq;
>>>> + int cpu;
>>>> +
>>>> + cpu = task_cpu(p);
>>>> +
>>>> + if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK)
>>>> + goto out;
>>>> +
>>>> + rq = cpu_rq(cpu);
>>>> +
>>>> + rcu_read_lock();
>>>> + curr = ACCESS_ONCE(rq->curr); /* unlocked access */
>>>> +
>>>> + /*
>>>> + * If we are dealing with a -deadline task, we must
>>>> + * decide where to wake it up.
>>>> + * If it has a later deadline and the current task
>>>> + * on this rq can't move (provided the waking task
>>>> + * can!) we prefer to send it somewhere else. On the
>>>> + * other hand, if it has a shorter deadline, we
>>>> + * try to make it stay here, it might be important.
>>>> + */
>>>> + if (unlikely(dl_task(curr)) &&
>>>> + (curr->nr_cpus_allowed < 2 ||
>>>> + !dl_entity_preempt(&p->dl, &curr->dl)) &&
>>>> + (p->nr_cpus_allowed > 1)) {
>>>> + int target = find_later_rq(p);
>>>> +
>>>> + if (target != -1)
>>>> + cpu = target;
>>>> + }
>>>> + rcu_read_unlock();
>>>> +
>>>> +out:
>>>> + return cpu;
>>>> +}
>>>> +
>>>> +static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
>>>> +{
>>>> + /*
>>>> + * Current can't be migrated, useless to reschedule,
>>>> + * let's hope p can move out.
>>>> + */
>>>> + if (rq->curr->nr_cpus_allowed == 1 ||
>>>> + latest_cpu_find(rq->rd->span, rq->curr, NULL) == -1)
>>>> + return;
>>>> +
>>>> + /*
>>>> + * p is migratable, so let's not schedule it and
>>>> + * see if it is pushed or pulled somewhere else.
>>>> + */
>>>> + if (p->nr_cpus_allowed != 1 &&
>>>> + latest_cpu_find(rq->rd->span, p, NULL) != -1)
>>>> + return;
>>>> +
>>>> + resched_task(rq->curr);
>>>> +}
>>>> +
>>>> +#endif /* CONFIG_SMP */
>>>> +
>>>> /*
>>>> * Only called when both the current and waking task are -deadline
>>>> * tasks.
>>>> @@ -532,8 +880,20 @@ static void yield_task_dl(struct rq *rq)
>>>> static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
>>>> int flags)
>>>> {
>>>> - if (dl_time_before(p->dl.deadline, rq->curr->dl.deadline))
>>>> + if (dl_entity_preempt(&p->dl, &rq->curr->dl)) {
>>>> resched_task(rq->curr);
>>>> + return;
>>>> + }
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> + /*
>>>> + * In the unlikely case current and p have the same deadline
>>>> + * let us try to decide what's the best thing to do...
>>>> + */
>>>> + if ((s64)(p->dl.deadline - rq->curr->dl.deadline) == 0 &&
>>>> + !need_resched())
>>>> + check_preempt_equal_dl(rq, p);
>>>> +#endif /* CONFIG_SMP */
>>>> }
>>>>
>>>> #ifdef CONFIG_SCHED_HRTICK
>>>> @@ -573,16 +933,29 @@ struct task_struct *pick_next_task_dl(struct rq *rq)
>>>>
>>>> p = dl_task_of(dl_se);
>>>> p->se.exec_start = rq_clock_task(rq);
>>>> +
>>>> + /* Running task will never be pushed. */
>>>> + if (p)
>>>> + dequeue_pushable_dl_task(rq, p);
>>>> +
>>>> #ifdef CONFIG_SCHED_HRTICK
>>>> if (hrtick_enabled(rq))
>>>> start_hrtick_dl(rq, p);
>>>> #endif
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> + rq->post_schedule = has_pushable_dl_tasks(rq);
>>>> +#endif /* CONFIG_SMP */
>>>> +
>>>> return p;
>>>> }
>>>>
>>>> static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
>>>> {
>>>> update_curr_dl(rq);
>>>> +
>>>> + if (on_dl_rq(&p->dl) && p->nr_cpus_allowed > 1)
>>>> + enqueue_pushable_dl_task(rq, p);
>>>> }
>>>>
>>>> static void task_tick_dl(struct rq *rq, struct task_struct *p, int queued)
>>>> @@ -616,16 +989,517 @@ static void set_curr_task_dl(struct rq *rq)
>>>> struct task_struct *p = rq->curr;
>>>>
>>>> p->se.exec_start = rq_clock_task(rq);
>>>> +
>>>> + /* You can't push away the running task */
>>>> + dequeue_pushable_dl_task(rq, p);
>>>> +}
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> +
>>>> +/* Only try algorithms three times */
>>>> +#define DL_MAX_TRIES 3
>>>> +
>>>> +static int pick_dl_task(struct rq *rq, struct task_struct *p, int cpu)
>>>> +{
>>>> + if (!task_running(rq, p) &&
>>>> + (cpu < 0 || cpumask_test_cpu(cpu, &p->cpus_allowed)) &&
>>>> + (p->nr_cpus_allowed > 1))
>>>> + return 1;
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +/* Returns the second earliest -deadline task, NULL otherwise */
>>>> +static struct task_struct *pick_next_earliest_dl_task(struct rq *rq, int cpu)
>>>> +{
>>>> + struct rb_node *next_node = rq->dl.rb_leftmost;
>>>> + struct sched_dl_entity *dl_se;
>>>> + struct task_struct *p = NULL;
>>>> +
>>>> +next_node:
>>>> + next_node = rb_next(next_node);
>>>> + if (next_node) {
>>>> + dl_se = rb_entry(next_node, struct sched_dl_entity, rb_node);
>>>> + p = dl_task_of(dl_se);
>>>> +
>>>> + if (pick_dl_task(rq, p, cpu))
>>>> + return p;
>>>> +
>>>> + goto next_node;
>>>> + }
>>>> +
>>>> + return NULL;
>>>> +}
>>>> +
>>>> +static int latest_cpu_find(struct cpumask *span,
>>>> + struct task_struct *task,
>>>> + struct cpumask *later_mask)
>>>> +{
>>>> + const struct sched_dl_entity *dl_se = &task->dl;
>>>> + int cpu, found = -1, best = 0;
>>>> + u64 max_dl = 0;
>>>> +
>>>> + for_each_cpu(cpu, span) {
>>>> + struct rq *rq = cpu_rq(cpu);
>>>> + struct dl_rq *dl_rq = &rq->dl;
>>>> +
>>>> + if (cpumask_test_cpu(cpu, &task->cpus_allowed) &&
>>>> + (!dl_rq->dl_nr_running || dl_time_before(dl_se->deadline,
>>>> + dl_rq->earliest_dl.curr))) {
>>>> + if (later_mask)
>>>> + cpumask_set_cpu(cpu, later_mask);
>>>> + if (!best && !dl_rq->dl_nr_running) {
>>>> + best = 1;
>>>> + found = cpu;
>>>> + } else if (!best &&
>>>> + dl_time_before(max_dl,
>>>> + dl_rq->earliest_dl.curr)) {
>>>
>>> Ug, the above is hard to read. What about:
>>>
>>> if (!best) {
>>> if (!dl_rq->dl_nr_running) {
>>> best = 1;
>>> found = cpu;
>>> } elsif (dl_time_before(...)) {
>>> ...
>>> }
>>> }
>>>
>>
>> This is completely removed in 13/14. I don't like it either, but since we end
>> up removing this mess, do you think we still have to fix this here?
>>
>>> Also, I would think dl should be nice to rt as well. There may be a
>>> idle CPU or a non rt task, and this could pick a CPU running an RT
>>> task. Worse yet, that RT task may be pinned to that CPU.
>>>
>>
>> Well, in 13/14 we introduce a free_cpus mask. A CPU is considered free if it
>> doesn't have any -deadline task running. We can modify that excluding also CPUs
>> running RT tasks, but I have to think a bit if we can do this also from -rt code.
>>
>>> We should be able to incorporate cpuprio_find() to be dl aware too.
>>> That is, work for both -rt and -dl.
>>>
>>
>> Like checking if a -dl task is running on the cpu chosen for pushing an -rt
>> task, and continue searching in that case.
>>
>>>
>>>
>>>> + max_dl = dl_rq->earliest_dl.curr;
>>>> + found = cpu;
>>>> + }
>>>> + } else if (later_mask)
>>>> + cpumask_clear_cpu(cpu, later_mask);
>>>> + }
>>>> +
>>>> + return found;
>>>> +}
>>>> +
>>>> +static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
>>>> +
>>>> +static int find_later_rq(struct task_struct *task)
>>>> +{
>>>> + struct sched_domain *sd;
>>>> + struct cpumask *later_mask = __get_cpu_var(local_cpu_mask_dl);
>>>> + int this_cpu = smp_processor_id();
>>>> + int best_cpu, cpu = task_cpu(task);
>>>> +
>>>> + /* Make sure the mask is initialized first */
>>>> + if (unlikely(!later_mask))
>>>> + return -1;
>>>> +
>>>> + if (task->nr_cpus_allowed == 1)
>>>> + return -1;
>>>> +
>>>> + best_cpu = latest_cpu_find(task_rq(task)->rd->span, task, later_mask);
>>>> + if (best_cpu == -1)
>>>> + return -1;
>>>> +
>>>> + /*
>>>> + * If we are here, some target has been found,
>>>> + * the most suitable of which is cached in best_cpu.
>>>> + * This is, among the runqueues where the current tasks
>>>> + * have later deadlines than the task's one, the rq
>>>> + * with the latest possible one.
>>>> + *
>>>> + * Now we check how well this matches with task's
>>>> + * affinity and system topology.
>>>> + *
>>>> + * The last cpu where the task run is our first
>>>> + * guess, since it is most likely cache-hot there.
>>>> + */
>>>> + if (cpumask_test_cpu(cpu, later_mask))
>>>> + return cpu;
>>>> + /*
>>>> + * Check if this_cpu is to be skipped (i.e., it is
>>>> + * not in the mask) or not.
>>>> + */
>>>> + if (!cpumask_test_cpu(this_cpu, later_mask))
>>>> + this_cpu = -1;
>>>> +
>>>> + rcu_read_lock();
>>>> + for_each_domain(cpu, sd) {
>>>> + if (sd->flags & SD_WAKE_AFFINE) {
>>>> +
>>>> + /*
>>>> + * If possible, preempting this_cpu is
>>>> + * cheaper than migrating.
>>>> + */
>>>> + if (this_cpu != -1 &&
>>>> + cpumask_test_cpu(this_cpu, sched_domain_span(sd))) {
>>>> + rcu_read_unlock();
>>>> + return this_cpu;
>>>> + }
>>>> +
>>>> + /*
>>>> + * Last chance: if best_cpu is valid and is
>>>> + * in the mask, that becomes our choice.
>>>> + */
>>>> + if (best_cpu < nr_cpu_ids &&
>>>> + cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {
>>>> + rcu_read_unlock();
>>>> + return best_cpu;
>>>> + }
>>>> + }
>>>> + }
>>>> + rcu_read_unlock();
>>>> +
>>>> + /*
>>>> + * At this point, all our guesses failed, we just return
>>>> + * 'something', and let the caller sort the things out.
>>>> + */
>>>> + if (this_cpu != -1)
>>>> + return this_cpu;
>>>> +
>>>> + cpu = cpumask_any(later_mask);
>>>> + if (cpu < nr_cpu_ids)
>>>> + return cpu;
>>>> +
>>>> + return -1;
>>>> +}
>>>> +
>>>> +/* Locks the rq it finds */
>>>> +static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
>>>> +{
>>>> + struct rq *later_rq = NULL;
>>>> + int tries;
>>>> + int cpu;
>>>> +
>>>> + for (tries = 0; tries < DL_MAX_TRIES; tries++) {
>>>> + cpu = find_later_rq(task);
>>>> +
>>>> + if ((cpu == -1) || (cpu == rq->cpu))
>>>> + break;
>>>> +
>>>> + later_rq = cpu_rq(cpu);
>>>> +
>>>> + /* Retry if something changed. */
>>>> + if (double_lock_balance(rq, later_rq)) {
>>>> + if (unlikely(task_rq(task) != rq ||
>>>> + !cpumask_test_cpu(later_rq->cpu,
>>>> + &task->cpus_allowed) ||
>>>> + task_running(rq, task) || !task->on_rq)) {
>>>> + double_unlock_balance(rq, later_rq);
>>>> + later_rq = NULL;
>>>> + break;
>>>> + }
>>>> + }
>>>> +
>>>> + /*
>>>> + * If the rq we found has no -deadline task, or
>>>> + * its earliest one has a later deadline than our
>>>> + * task, the rq is a good one.
>>>> + */
>>>> + if (!later_rq->dl.dl_nr_running ||
>>>> + dl_time_before(task->dl.deadline,
>>>> + later_rq->dl.earliest_dl.curr))
>>>> + break;
>>>> +
>>>> + /* Otherwise we try again. */
>>>> + double_unlock_balance(rq, later_rq);
>>>> + later_rq = NULL;
>>>> + }
>>>> +
>>>> + return later_rq;
>>>> }
>>>>
>>>> +static struct task_struct *pick_next_pushable_dl_task(struct rq *rq)
>>>> +{
>>>> + struct task_struct *p;
>>>> +
>>>> + if (!has_pushable_dl_tasks(rq))
>>>> + return NULL;
>>>> +
>>>> + p = rb_entry(rq->dl.pushable_dl_tasks_leftmost,
>>>> + struct task_struct, pushable_dl_tasks);
>>>> +
>>>> + BUG_ON(rq->cpu != task_cpu(p));
>>>> + BUG_ON(task_current(rq, p));
>>>> + BUG_ON(p->nr_cpus_allowed <= 1);
>>>> +
>>>> + BUG_ON(!p->se.on_rq);
>>>> + BUG_ON(!dl_task(p));
>>>> +
>>>> + return p;
>>>> +}
>>>> +
>>>> +/*
>>>> + * See if the non running -deadline tasks on this rq
>>>> + * can be sent to some other CPU where they can preempt
>>>> + * and start executing.
>>>> + */
>>>> +static int push_dl_task(struct rq *rq)
>>>> +{
>>>> + struct task_struct *next_task;
>>>> + struct rq *later_rq;
>>>> +
>>>> + if (!rq->dl.overloaded)
>>>> + return 0;
>>>> +
>>>> + next_task = pick_next_pushable_dl_task(rq);
>>>> + if (!next_task)
>>>> + return 0;
>>>> +
>>>> +retry:
>>>> + if (unlikely(next_task == rq->curr)) {
>>>> + WARN_ON(1);
>>>> + return 0;
>>>> + }
>>>> +
>>>> + /*
>>>> + * If next_task preempts rq->curr, and rq->curr
>>>> + * can move away, it makes sense to just reschedule
>>>> + * without going further in pushing next_task.
>>>> + */
>>>> + if (dl_task(rq->curr) &&
>>>> + dl_time_before(next_task->dl.deadline, rq->curr->dl.deadline) &&
>>>> + rq->curr->nr_cpus_allowed > 1) {
>>>> + resched_task(rq->curr);
>>>> + return 0;
>>>> + }
>>>> +
>>>> + /* We might release rq lock */
>>>> + get_task_struct(next_task);
>>>> +
>>>> + /* Will lock the rq it'll find */
>>>> + later_rq = find_lock_later_rq(next_task, rq);
>>>> + if (!later_rq) {
>>>> + struct task_struct *task;
>>>> +
>>>> + /*
>>>> + * We must check all this again, since
>>>> + * find_lock_later_rq releases rq->lock and it is
>>>> + * then possible that next_task has migrated.
>>>> + */
>>>> + task = pick_next_pushable_dl_task(rq);
>>>> + if (task_cpu(next_task) == rq->cpu && task == next_task) {
>>>> + /*
>>>> + * The task is still there. We don't try
>>>> + * again, some other cpu will pull it when ready.
>>>> + */
>>>> + dequeue_pushable_dl_task(rq, next_task);
>>>> + goto out;
>>>> + }
>>>> +
>>>> + if (!task)
>>>> + /* No more tasks */
>>>> + goto out;
>>>> +
>>>> + put_task_struct(next_task);
>>>> + next_task = task;
>>>> + goto retry;
>>>> + }
>>>> +
>>>> + deactivate_task(rq, next_task, 0);
>>>> + set_task_cpu(next_task, later_rq->cpu);
>>>> + activate_task(later_rq, next_task, 0);
>>>> +
>>>> + resched_task(later_rq->curr);
>>>> +
>>>> + double_unlock_balance(rq, later_rq);
>>>> +
>>>> +out:
>>>> + put_task_struct(next_task);
>>>> +
>>>> + return 1;
>>>> +}
>>>> +
>>>> +static void push_dl_tasks(struct rq *rq)
>>>> +{
>>>> + /* Terminates as it moves a -deadline task */
>>>> + while (push_dl_task(rq))
>>>> + ;
>>>> +}
>>>> +
>>>> +static int pull_dl_task(struct rq *this_rq)
>>>> +{
>>>> + int this_cpu = this_rq->cpu, ret = 0, cpu;
>>>> + struct task_struct *p;
>>>> + struct rq *src_rq;
>>>> + u64 dmin = LONG_MAX;
>>>> +
>>>> + if (likely(!dl_overloaded(this_rq)))
>>>> + return 0;
>>>> +
>>>> + /*
>>>> + * Match the barrier from dl_set_overloaded; this guarantees that if we
>>>> + * see overloaded we must also see the dlo_mask bit.
>>>> + */
>>>> + smp_rmb();
>>>> +
>>>> + for_each_cpu(cpu, this_rq->rd->dlo_mask) {
>>>> + if (this_cpu == cpu)
>>>> + continue;
>>>> +
>>>> + src_rq = cpu_rq(cpu);
>>>> +
>>>> + /*
>>>> + * It looks racy, abd it is! However, as in sched_rt.c,
>>>
>>> abd it is?
>>>
>>
>> Oops!
>>
>> Thanks,
>>
>> - Juri
>>
>>>
>>>> + * we are fine with this.
>>>> + */
>>>> + if (this_rq->dl.dl_nr_running &&
>>>> + dl_time_before(this_rq->dl.earliest_dl.curr,
>>>> + src_rq->dl.earliest_dl.next))
>>>> + continue;
>>>> +
>>>> + /* Might drop this_rq->lock */
>>>> + double_lock_balance(this_rq, src_rq);
>>>> +
>>>> + /*
>>>> + * If there are no more pullable tasks on the
>>>> + * rq, we're done with it.
>>>> + */
>>>> + if (src_rq->dl.dl_nr_running <= 1)
>>>> + goto skip;
>>>> +
>>>> + p = pick_next_earliest_dl_task(src_rq, this_cpu);
>>>> +
>>>> + /*
>>>> + * We found a task to be pulled if:
>>>> + * - it preempts our current (if there's one),
>>>> + * - it will preempt the last one we pulled (if any).
>>>> + */
>>>> + if (p && dl_time_before(p->dl.deadline, dmin) &&
>>>> + (!this_rq->dl.dl_nr_running ||
>>>> + dl_time_before(p->dl.deadline,
>>>> + this_rq->dl.earliest_dl.curr))) {
>>>> + WARN_ON(p == src_rq->curr);
>>>> + WARN_ON(!p->se.on_rq);
>>>> +
>>>> + /*
>>>> + * Then we pull iff p has actually an earlier
>>>> + * deadline than the current task of its runqueue.
>>>> + */
>>>> + if (dl_time_before(p->dl.deadline,
>>>> + src_rq->curr->dl.deadline))
>>>> + goto skip;
>>>> +
>>>> + ret = 1;
>>>> +
>>>> + deactivate_task(src_rq, p, 0);
>>>> + set_task_cpu(p, this_cpu);
>>>> + activate_task(this_rq, p, 0);
>>>> + dmin = p->dl.deadline;
>>>> +
>>>> + /* Is there any other task even earlier? */
>>>> + }
>>>> +skip:
>>>> + double_unlock_balance(this_rq, src_rq);
>>>> + }
>>>> +
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static void pre_schedule_dl(struct rq *rq, struct task_struct *prev)
>>>> +{
>>>> + /* Try to pull other tasks here */
>>>> + if (dl_task(prev))
>>>> + pull_dl_task(rq);
>>>> +}
>>>> +
>>>> +static void post_schedule_dl(struct rq *rq)
>>>> +{
>>>> + push_dl_tasks(rq);
>>>> +}
>>>> +
>>>> +/*
>>>> + * Since the task is not running and a reschedule is not going to happen
>>>> + * anytime soon on its runqueue, we try pushing it away now.
>>>> + */
>>>> +static void task_woken_dl(struct rq *rq, struct task_struct *p)
>>>> +{
>>>> + if (!task_running(rq, p) &&
>>>> + !test_tsk_need_resched(rq->curr) &&
>>>> + has_pushable_dl_tasks(rq) &&
>>>> + p->nr_cpus_allowed > 1 &&
>>>> + dl_task(rq->curr) &&
>>>> + (rq->curr->nr_cpus_allowed < 2 ||
>>>> + dl_entity_preempt(&rq->curr->dl, &p->dl))) {
>>>> + push_dl_tasks(rq);
>>>> + }
>>>> +}
>>>> +
>>>> +static void set_cpus_allowed_dl(struct task_struct *p,
>>>> + const struct cpumask *new_mask)
>>>> +{
>>>> + struct rq *rq;
>>>> + int weight;
>>>> +
>>>> + BUG_ON(!dl_task(p));
>>>> +
>>>> + /*
>>>> + * Update only if the task is actually running (i.e.,
>>>> + * it is on the rq AND it is not throttled).
>>>> + */
>>>> + if (!on_dl_rq(&p->dl))
>>>> + return;
>>>> +
>>>> + weight = cpumask_weight(new_mask);
>>>> +
>>>> + /*
>>>> + * Only update if the process changes its state from whether it
>>>> + * can migrate or not.
>>>> + */
>>>> + if ((p->nr_cpus_allowed > 1) == (weight > 1))
>>>> + return;
>>>> +
>>>> + rq = task_rq(p);
>>>> +
>>>> + /*
>>>> + * The process used to be able to migrate OR it can now migrate
>>>> + */
>>>> + if (weight <= 1) {
>>>> + if (!task_current(rq, p))
>>>> + dequeue_pushable_dl_task(rq, p);
>>>> + BUG_ON(!rq->dl.dl_nr_migratory);
>>>> + rq->dl.dl_nr_migratory--;
>>>> + } else {
>>>> + if (!task_current(rq, p))
>>>> + enqueue_pushable_dl_task(rq, p);
>>>> + rq->dl.dl_nr_migratory++;
>>>> + }
>>>> +
>>>> + update_dl_migration(&rq->dl);
>>>> +}
>>>> +
>>>> +/* Assumes rq->lock is held */
>>>> +static void rq_online_dl(struct rq *rq)
>>>> +{
>>>> + if (rq->dl.overloaded)
>>>> + dl_set_overload(rq);
>>>> +}
>>>> +
>>>> +/* Assumes rq->lock is held */
>>>> +static void rq_offline_dl(struct rq *rq)
>>>> +{
>>>> + if (rq->dl.overloaded)
>>>> + dl_clear_overload(rq);
>>>> +}
>>>> +
>>>> +void init_sched_dl_class(void)
>>>> +{
>>>> + unsigned int i;
>>>> +
>>>> + for_each_possible_cpu(i)
>>>> + zalloc_cpumask_var_node(&per_cpu(local_cpu_mask_dl, i),
>>>> + GFP_KERNEL, cpu_to_node(i));
>>>> +}
>>>> +
>>>> +#endif /* CONFIG_SMP */
>>>> +
>>>> static void switched_from_dl(struct rq *rq, struct task_struct *p)
>>>> {
>>>> - if (hrtimer_active(&p->dl.dl_timer))
>>>> + if (hrtimer_active(&p->dl.dl_timer) && !dl_policy(p->policy))
>>>> hrtimer_try_to_cancel(&p->dl.dl_timer);
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> + /*
>>>> + * Since this might be the only -deadline task on the rq,
>>>> + * this is the right place to try to pull some other one
>>>> + * from an overloaded cpu, if any.
>>>> + */
>>>> + if (!rq->dl.dl_nr_running)
>>>> + pull_dl_task(rq);
>>>> +#endif
>>>> }
>>>>
>>>> +/*
>>>> + * When switching to -deadline, we may overload the rq, then
>>>> + * we try to push someone off, if possible.
>>>> + */
>>>> static void switched_to_dl(struct rq *rq, struct task_struct *p)
>>>> {
>>>> + int check_resched = 1;
>>>> +
>>>> /*
>>>> * If p is throttled, don't consider the possibility
>>>> * of preempting rq->curr, the check will be done right
>>>> @@ -635,26 +1509,53 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
>>>> return;
>>>>
>>>> if (!p->on_rq || rq->curr != p) {
>>>> - if (task_has_dl_policy(rq->curr))
>>>> +#ifdef CONFIG_SMP
>>>> + if (rq->dl.overloaded && push_dl_task(rq) && rq != task_rq(p))
>>>> + /* Only reschedule if pushing failed */
>>>> + check_resched = 0;
>>>> +#endif /* CONFIG_SMP */
>>>> + if (check_resched && task_has_dl_policy(rq->curr))
>>>> check_preempt_curr_dl(rq, p, 0);
>>>> - else
>>>> - resched_task(rq->curr);
>>>> }
>>>> }
>>>>
>>>> +/*
>>>> + * If the scheduling parameters of a -deadline task changed,
>>>> + * a push or pull operation might be needed.
>>>> + */
>>>> static void prio_changed_dl(struct rq *rq, struct task_struct *p,
>>>> int oldprio)
>>>> {
>>>> - switched_to_dl(rq, p);
>>>> -}
>>>> -
>>>> + if (p->on_rq || rq->curr == p) {
>>>> #ifdef CONFIG_SMP
>>>> -static int
>>>> -select_task_rq_dl(struct task_struct *p, int sd_flag, int flags)
>>>> -{
>>>> - return task_cpu(p);
>>>> + /*
>>>> + * This might be too much, but unfortunately
>>>> + * we don't have the old deadline value, and
>>>> + * we can't argue if the task is increasing
>>>> + * or lowering its prio, so...
>>>> + */
>>>> + if (!rq->dl.overloaded)
>>>> + pull_dl_task(rq);
>>>> +
>>>> + /*
>>>> + * If we now have a earlier deadline task than p,
>>>> + * then reschedule, provided p is still on this
>>>> + * runqueue.
>>>> + */
>>>> + if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
>>>> + rq->curr == p)
>>>> + resched_task(p);
>>>> +#else
>>>> + /*
>>>> + * Again, we don't know if p has a earlier
>>>> + * or later deadline, so let's blindly set a
>>>> + * (maybe not needed) rescheduling point.
>>>> + */
>>>> + resched_task(p);
>>>> +#endif /* CONFIG_SMP */
>>>> + } else
>>>> + switched_to_dl(rq, p);
>>>> }
>>>> -#endif
>>>>
>>>> const struct sched_class dl_sched_class = {
>>>> .next = &rt_sched_class,
>>>> @@ -669,6 +1570,12 @@ const struct sched_class dl_sched_class = {
>>>>
>>>> #ifdef CONFIG_SMP
>>>> .select_task_rq = select_task_rq_dl,
>>>> + .set_cpus_allowed = set_cpus_allowed_dl,
>>>> + .rq_online = rq_online_dl,
>>>> + .rq_offline = rq_offline_dl,
>>>> + .pre_schedule = pre_schedule_dl,
>>>> + .post_schedule = post_schedule_dl,
>>>> + .task_woken = task_woken_dl,
>>>> #endif
>>>>
>>>> .set_curr_task = set_curr_task_dl,
>>>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>>>> index 01970c8..f7c4881 100644
>>>> --- a/kernel/sched/rt.c
>>>> +++ b/kernel/sched/rt.c
>>>> @@ -1720,7 +1720,7 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
>>>> !test_tsk_need_resched(rq->curr) &&
>>>> has_pushable_tasks(rq) &&
>>>> p->nr_cpus_allowed > 1 &&
>>>> - rt_task(rq->curr) &&
>>>> + (dl_task(rq->curr) || rt_task(rq->curr)) &&
>>>> (rq->curr->nr_cpus_allowed < 2 ||
>>>> rq->curr->prio <= p->prio))
>>>> push_rt_tasks(rq);
>>>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>>>> index ba97476..70d0030 100644
>>>> --- a/kernel/sched/sched.h
>>>> +++ b/kernel/sched/sched.h
>>>> @@ -383,6 +383,31 @@ struct dl_rq {
>>>> struct rb_node *rb_leftmost;
>>>>
>>>> unsigned long dl_nr_running;
>>>> +
>>>> +#ifdef CONFIG_SMP
>>>> + /*
>>>> + * Deadline values of the currently executing and the
>>>> + * earliest ready task on this rq. Caching these facilitates
>>>> + * the decision wether or not a ready but not running task
>>>> + * should migrate somewhere else.
>>>> + */
>>>> + struct {
>>>> + u64 curr;
>>>> + u64 next;
>>>> + } earliest_dl;
>>>> +
>>>> + unsigned long dl_nr_migratory;
>>>> + unsigned long dl_nr_total;
>>>> + int overloaded;
>>>> +
>>>> + /*
>>>> + * Tasks on this rq that can be pushed away. They are kept in
>>>> + * an rb-tree, ordered by tasks' deadlines, with caching
>>>> + * of the leftmost (earliest deadline) element.
>>>> + */
>>>> + struct rb_root pushable_dl_tasks_root;
>>>> + struct rb_node *pushable_dl_tasks_leftmost;
>>>> +#endif
>>>> };
>>>>
>>>> #ifdef CONFIG_SMP
>>>> @@ -403,6 +428,13 @@ struct root_domain {
>>>> cpumask_var_t online;
>>>>
>>>> /*
>>>> + * The bit corresponding to a CPU gets set here if such CPU has more
>>>> + * than one runnable -deadline task (as it is below for RT tasks).
>>>> + */
>>>> + cpumask_var_t dlo_mask;
>>>> + atomic_t dlo_count;
>>>> +
>>>> + /*
>>>> * The "RT overload" flag: it gets set if a CPU has more than
>>>> * one runnable RT task.
>>>> */
>>>> @@ -1063,6 +1095,8 @@ static inline void idle_balance(int cpu, struct rq *rq)
>>>> extern void sysrq_sched_debug_show(void);
>>>> extern void sched_init_granularity(void);
>>>> extern void update_max_interval(void);
>>>> +
>>>> +extern void init_sched_dl_class(void);
>>>> extern void init_sched_rt_class(void);
>>>> extern void init_sched_fair_class(void);
>>>>
>>>
>>
>>
>
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