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    SubjectRe: [PATCH 04/14] sched: SCHED_DEADLINE SMP-related data structures & logic.
    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@gmail.com> 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@linux.it>,
    > >> + * Juri Lelli <juri.lelli@gmail.com>,
    > >> * Michael Trimarchi <michael@amarulasolutions.com>,
    > >> * Fabio Checconi <fchecconi@gmail.com>
    > >> */
    > >> @@ -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. ;-)

    Thanx, Paul

    > >> + 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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