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Commit a64692a3 authored by Mike Galbraith's avatar Mike Galbraith Committed by Ingo Molnar
Browse files

sched: Cleanup/optimize clock updates 



Now that we no longer depend on the clock being updated prior to enqueueing
on migratory wakeup, we can clean up a bit, placing calls to update_rq_clock()
exactly where they are needed, ie on enqueue, dequeue and schedule events.

In the case of a freshly enqueued task immediately preempting, we can skip the
update during preemption, as the clock was just updated by the enqueue event.
We also save an unneeded call during a migratory wakeup by not updating the
previous runqueue, where update_curr() won't be invoked.

Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1268301199.6785.32.camel@marge.simson.net>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent e12f31d3

kernel/sched.c

+16 −16
Original line number Diff line number Diff line
@@ -495,6 +495,8 @@ struct rq { 
	u64 nohz_stamp;

	unsigned char in_nohz_recently;

#endif

	unsigned int skip_clock_update;



	/* capture load from *all* tasks on this cpu: */

	struct load_weight load;

	unsigned long nr_load_updates;
@@ -592,6 +594,13 @@ static inline 
void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)

{

	rq->curr->sched_class->check_preempt_curr(rq, p, flags);



	/*

	 * A queue event has occurred, and we're going to schedule.  In

	 * this case, we can save a useless back to back clock update.

	 */

	if (test_tsk_need_resched(p))

		rq->skip_clock_update = 1;

}



static inline int cpu_of(struct rq *rq)
@@ -626,6 +635,7 @@ static inline int cpu_of(struct rq *rq) 


inline void update_rq_clock(struct rq *rq)

{

	if (!rq->skip_clock_update)

		rq->clock = sched_clock_cpu(cpu_of(rq));

}
@@ -1782,8 +1792,6 @@ static void double_rq_lock(struct rq *rq1, struct rq *rq2) 
			raw_spin_lock_nested(&rq1->lock, SINGLE_DEPTH_NESTING);

		}

	}

	update_rq_clock(rq1);

	update_rq_clock(rq2);

}



/*
@@ -1880,6 +1888,7 @@ static void update_avg(u64 *avg, u64 sample) 
static void

enqueue_task(struct rq *rq, struct task_struct *p, int wakeup, bool head)

{

	update_rq_clock(rq);

	sched_info_queued(p);

	p->sched_class->enqueue_task(rq, p, wakeup, head);

	p->se.on_rq = 1;
@@ -1887,6 +1896,7 @@ enqueue_task(struct rq *rq, struct task_struct *p, int wakeup, bool head) 


static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)

{

	update_rq_clock(rq);

	sched_info_dequeued(p);

	p->sched_class->dequeue_task(rq, p, sleep);

	p->se.on_rq = 0;
@@ -2366,7 +2376,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, 


	smp_wmb();

	rq = task_rq_lock(p, &flags);

	update_rq_clock(rq);

	if (!(p->state & state))

		goto out;
@@ -2407,7 +2416,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, 


	rq = cpu_rq(cpu);

	raw_spin_lock(&rq->lock);

	update_rq_clock(rq);



	/*

	 * We migrated the task without holding either rq->lock, however
@@ -2624,7 +2632,6 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags) 


	BUG_ON(p->state != TASK_WAKING);

	p->state = TASK_RUNNING;

	update_rq_clock(rq);

	activate_task(rq, p, 0);

	trace_sched_wakeup_new(rq, p, 1);

	check_preempt_curr(rq, p, WF_FORK);
@@ -3578,6 +3585,9 @@ static inline void schedule_debug(struct task_struct *prev) 


static void put_prev_task(struct rq *rq, struct task_struct *prev)

{

	if (prev->se.on_rq)

		update_rq_clock(rq);

	rq->skip_clock_update = 0;

	prev->sched_class->put_prev_task(rq, prev);

}
@@ -3640,7 +3650,6 @@ need_resched_nonpreemptible: 
		hrtick_clear(rq);



	raw_spin_lock_irq(&rq->lock);

	update_rq_clock(rq);

	clear_tsk_need_resched(prev);



	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
@@ -4197,7 +4206,6 @@ void rt_mutex_setprio(struct task_struct *p, int prio) 
	BUG_ON(prio < 0 || prio > MAX_PRIO);



	rq = task_rq_lock(p, &flags);

	update_rq_clock(rq);



	oldprio = p->prio;

	prev_class = p->sched_class;
@@ -4240,7 +4248,6 @@ void set_user_nice(struct task_struct *p, long nice) 
	 * the task might be in the middle of scheduling on another CPU.

	 */

	rq = task_rq_lock(p, &flags);

	update_rq_clock(rq);

	/*

	 * The RT priorities are set via sched_setscheduler(), but we still

	 * allow the 'normal' nice value to be set - but as expected
@@ -4523,7 +4530,6 @@ recheck: 
		raw_spin_unlock_irqrestore(&p->pi_lock, flags);

		goto recheck;

	}

	update_rq_clock(rq);

	on_rq = p->se.on_rq;

	running = task_current(rq, p);

	if (on_rq)
@@ -5530,7 +5536,6 @@ void sched_idle_next(void) 


	__setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);



	update_rq_clock(rq);

	activate_task(rq, p, 0);



	raw_spin_unlock_irqrestore(&rq->lock, flags);
@@ -5585,7 +5590,6 @@ static void migrate_dead_tasks(unsigned int dead_cpu) 
	for ( ; ; ) {

		if (!rq->nr_running)

			break;

		update_rq_clock(rq);

		next = pick_next_task(rq);

		if (!next)

			break;
@@ -5869,7 +5873,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) 
		rq->migration_thread = NULL;

		/* Idle task back to normal (off runqueue, low prio) */

		raw_spin_lock_irq(&rq->lock);

		update_rq_clock(rq);

		deactivate_task(rq, rq->idle, 0);

		__setscheduler(rq, rq->idle, SCHED_NORMAL, 0);

		rq->idle->sched_class = &idle_sched_class;
@@ -7815,7 +7818,6 @@ static void normalize_task(struct rq *rq, struct task_struct *p) 
{

	int on_rq;



	update_rq_clock(rq);

	on_rq = p->se.on_rq;

	if (on_rq)

		deactivate_task(rq, p, 0);
@@ -8177,8 +8179,6 @@ void sched_move_task(struct task_struct *tsk) 


	rq = task_rq_lock(tsk, &flags);



	update_rq_clock(rq);



	running = task_current(rq, tsk);

	on_rq = tsk->se.on_rq;

kernel/sched_fair.c

+0 −2
Original line number Diff line number Diff line
@@ -3064,8 +3064,6 @@ static void active_load_balance(struct rq *busiest_rq, int busiest_cpu) 


	/* move a task from busiest_rq to target_rq */

	double_lock_balance(busiest_rq, target_rq);

	update_rq_clock(busiest_rq);

	update_rq_clock(target_rq);



	/* Search for an sd spanning us and the target CPU. */

	for_each_domain(target_cpu, sd) {