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Message-ID: <528E1508.7060305@gmail.com>
Date: Thu, 21 Nov 2013 15:13:28 +0100
From: Juri Lelli <juri.lelli@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
CC: peterz@...radead.org, tglx@...utronix.de, mingo@...hat.com,
oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
johan.eker@...csson.com, p.faure@...tech.ch,
linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
michael@...rulasolutions.com, fchecconi@...il.com,
tommaso.cucinotta@...up.it, nicola.manica@...i.unitn.it,
luca.abeni@...tn.it, dhaval.giani@...il.com, hgu1972@...il.com,
paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
insop.song@...il.com, liming.wang@...driver.com, jkacur@...hat.com,
harald.gustafsson@...csson.com, vincent.guittot@...aro.org,
bruce.ashfield@...driver.com
Subject: Re: [PATCH 04/14] sched: SCHED_DEADLINE SMP-related data structures
& logic.
On 11/20/2013 07:51 PM, Steven Rostedt wrote:
> On Thu, 7 Nov 2013 14:43:38 +0100
> Juri Lelli <juri.lelli@...il.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@...ux.it>,
>> + * Juri Lelli <juri.lelli@...il.com>,
>> * Michael Trimarchi <michael@...rulasolutions.com>,
>> * Fabio Checconi <fchecconi@...il.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.
>
>> + 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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