Re: [PATCH 01/18] sched: Replace post_schedule with a balance callback list

Kirill Tkhai
2015-06-11T15:32:22Z

A just came thought

В Чт, 11/06/2015 в 14:46 +0200, Peter Zijlstra пишет:
> Generalize the post_schedule() stuff into a balance callback list.
> This allows us to more easily use it outside of schedule() and cross
> sched_class.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/sched/core.c | 36 ++++++++++++++++++++++++------------
> kernel/sched/deadline.c | 21 +++++++++++----------
> kernel/sched/rt.c | 25 +++++++++++--------------
> kernel/sched/sched.h | 19 +++++++++++++++++--
> 4 files changed, 63 insertions(+), 38 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2277,23 +2277,35 @@ static struct rq *finish_task_switch(str
> #ifdef CONFIG_SMP
>
> /* rq->lock is NOT held, but preemption is disabled */
> -static inline void post_schedule(struct rq *rq)
> +static void __balance_callback(struct rq *rq)
> {
> - if (rq->post_schedule) {
> - unsigned long flags;
> + struct callback_head *head, *next;
> + void (*func)(struct rq *rq);
> + unsigned long flags;
>
> - raw_spin_lock_irqsave(&rq->lock, flags);
> - if (rq->curr->sched_class->post_schedule)
> - rq->curr->sched_class->post_schedule(rq);
> - raw_spin_unlock_irqrestore(&rq->lock, flags);
> + raw_spin_lock_irqsave(&rq->lock, flags);
> + head = rq->balance_callback;
> + rq->balance_callback = NULL;
> + while (head) {
> + func = (void (*)(struct rq *))head->func;
> + next = head->next;
> + head->next = NULL;
> + head = next;
>
> - rq->post_schedule = 0;
> + func(rq);
> }
> + raw_spin_unlock_irqrestore(&rq->lock, flags);
> +}
> +
> +static inline void balance_callback(struct rq *rq)
> +{
> + if (unlikely(rq->balance_callback))
> + __balance_callback(rq);
> }
>
> #else
>
> -static inline void post_schedule(struct rq *rq)
> +static inline void balance_callback(struct rq *rq)
> {
> }
>
> @@ -2311,7 +2323,7 @@ asmlinkage __visible void schedule_tail(
> /* finish_task_switch() drops rq->lock and enables preemtion */
> preempt_disable();
> rq = finish_task_switch(prev);
> - post_schedule(rq);
> + balance_callback(rq);
> preempt_enable();
>
> if (current->set_child_tid)
> @@ -2822,7 +2834,7 @@ static void __sched __schedule(void)
> } else
> raw_spin_unlock_irq(&rq->lock);
>
> - post_schedule(rq);
> + balance_callback(rq);
> }
>
> static inline void sched_submit_work(struct task_struct *tsk)
> @@ -7216,7 +7228,7 @@ void __init sched_init(void)
> rq->sd = NULL;
> rq->rd = NULL;
> rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE;
> - rq->post_schedule = 0;
> + rq->balance_callback = NULL;
> rq->active_balance = 0;
> rq->next_balance = jiffies;
> rq->push_cpu = 0;
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -213,9 +213,16 @@ static inline bool need_pull_dl_task(str
> return dl_task(prev);
> }
>
> -static inline void set_post_schedule(struct rq *rq)
> +static DEFINE_PER_CPU(struct callback_head, dl_balance_head);
> +
> +static void push_dl_tasks(struct rq *);
> +
> +static inline void queue_push_tasks(struct rq *rq)
> {
> - rq->post_schedule = has_pushable_dl_tasks(rq);
> + if (!has_pushable_dl_tasks(rq))
> + return;
> +
> + queue_balance_callback(rq, &per_cpu(dl_balance_head, rq->cpu), push_dl_tasks);
> }
>
> static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq);
> @@ -296,7 +303,7 @@ static inline int pull_dl_task(struct rq
> return 0;
> }
>
> -static inline void set_post_schedule(struct rq *rq)
> +static inline void queue_push_tasks(struct rq *rq)
> {
> }
> #endif /* CONFIG_SMP */
> @@ -1126,7 +1133,7 @@ struct task_struct *pick_next_task_dl(st
> if (hrtick_enabled(rq))
> start_hrtick_dl(rq, p);
>
> - set_post_schedule(rq);
> + queue_push_tasks(rq);
>
> return p;
> }
> @@ -1544,11 +1551,6 @@ static int pull_dl_task(struct rq *this_
> return ret;
> }
>
> -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.
> @@ -1784,7 +1786,6 @@ const struct sched_class dl_sched_class
> .set_cpus_allowed = set_cpus_allowed_dl,
> .rq_online = rq_online_dl,
> .rq_offline = rq_offline_dl,
> - .post_schedule = post_schedule_dl,
> .task_woken = task_woken_dl,
> #endif
>
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -354,13 +354,16 @@ static inline int has_pushable_tasks(str
> return !plist_head_empty(&rq->rt.pushable_tasks);
> }
>
> -static inline void set_post_schedule(struct rq *rq)
> +static DEFINE_PER_CPU(struct callback_head, rt_balance_head);
> +
> +static void push_rt_tasks(struct rq *);
> +
> +static inline void queue_push_tasks(struct rq *rq)
> {
> - /*
> - * We detect this state here so that we can avoid taking the RQ
> - * lock again later if there is no need to push
> - */
> - rq->post_schedule = has_pushable_tasks(rq);
> + if (!has_pushable_tasks(rq))
> + return;
> +
> + queue_balance_callback(rq, &per_cpu(rt_balance_head, rq->cpu), push_rt_tasks);
> }
>
> static void enqueue_pushable_task(struct rq *rq, struct task_struct *p)
> @@ -417,7 +420,7 @@ static inline int pull_rt_task(struct rq
> return 0;
> }
>
> -static inline void set_post_schedule(struct rq *rq)
> +static inline void queue_push_tasks(struct rq *rq)
> {
> }
> #endif /* CONFIG_SMP */
> @@ -1497,7 +1500,7 @@ pick_next_task_rt(struct rq *rq, struct
> /* The running task is never eligible for pushing */
> dequeue_pushable_task(rq, p);
>
> - set_post_schedule(rq);
> + queue_push_tasks(rq);
>
> return p;
> }
> @@ -2042,11 +2045,6 @@ static int pull_rt_task(struct rq *this_
> return ret;
> }
>
> -static void post_schedule_rt(struct rq *rq)
> -{
> - push_rt_tasks(rq);
> -}
> -
> /*
> * If we are not running and we are not going to reschedule soon, we should
> * try to push tasks away now
> @@ -2318,7 +2316,6 @@ const struct sched_class rt_sched_class
> .set_cpus_allowed = set_cpus_allowed_rt,
> .rq_online = rq_online_rt,
> .rq_offline = rq_offline_rt,
> - .post_schedule = post_schedule_rt,
> .task_woken = task_woken_rt,
> .switched_from = switched_from_rt,
> #endif
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -624,9 +624,10 @@ struct rq {
> unsigned long cpu_capacity;
> unsigned long cpu_capacity_orig;
>
> + struct callback_head *balance_callback;
> +
> unsigned char idle_balance;
> /* For active balancing */
> - int post_schedule;
> int active_balance;
> int push_cpu;
> struct cpu_stop_work active_balance_work;
> @@ -767,6 +768,21 @@ extern int migrate_swap(struct task_stru
>
> #ifdef CONFIG_SMP
>
> +static inline void
> +queue_balance_callback(struct rq *rq,
> + struct callback_head *head,
> + void (*func)(struct rq *rq))
> +{
> + lockdep_assert_held(&rq->lock);
> +
> + if (unlikely(head->next))
> + return;
> +
> + head->func = (void (*)(struct callback_head *))func;
> + head->next = rq->balance_callback;
> + rq->balance_callback = head;
> +}

Maybe, we should queue a higher priority callback at the head?
And set aside a callback, which class's priority lower rq->curr's.

> +
> extern void sched_ttwu_pending(void);
>
> #define rcu_dereference_check_sched_domain(p) \
> @@ -1192,7 +1208,6 @@ struct sched_class {
> int (*select_task_rq)(struct task_struct *p, int task_cpu, int sd_flag, int flags);
> void (*migrate_task_rq)(struct task_struct *p, int next_cpu);
>
> - void (*post_schedule) (struct rq *this_rq);
> void (*task_waking) (struct task_struct *task);
> void (*task_woken) (struct rq *this_rq, struct task_struct *task);
>
>
>