Commit 2a2f5d4e authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/fair: Rewrite cfs_rq->removed_*avg 



Since on wakeup migration we don't hold the rq->lock for the old CPU
we cannot update its state. Instead we add the removed 'load' to an
atomic variable and have the next update on that CPU collect and
process it.

Currently we have 2 atomic variables; which already have the issue
that they can be read out-of-sync. Also, two atomic ops on a single
cacheline is already more expensive than an uncontended lock.

Since we want to add more, convert the thing over to an explicit
cacheline with a lock in.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9059393e

kernel/sched/debug.c

+4 −4
Original line number Diff line number Diff line
@@ -564,10 +564,10 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) 
			cfs_rq->runnable_load_avg);

	SEQ_printf(m, "  .%-30s: %lu\n", "util_avg",

			cfs_rq->avg.util_avg);

	SEQ_printf(m, "  .%-30s: %ld\n", "removed_load_avg",

			atomic_long_read(&cfs_rq->removed_load_avg));

	SEQ_printf(m, "  .%-30s: %ld\n", "removed_util_avg",

			atomic_long_read(&cfs_rq->removed_util_avg));

	SEQ_printf(m, "  .%-30s: %ld\n", "removed.load_avg",

			cfs_rq->removed.load_avg);

	SEQ_printf(m, "  .%-30s: %ld\n", "removed.util_avg",

			cfs_rq->removed.util_avg);

#ifdef CONFIG_FAIR_GROUP_SCHED

	SEQ_printf(m, "  .%-30s: %lu\n", "tg_load_avg_contrib",

			cfs_rq->tg_load_avg_contrib);

kernel/sched/fair.c

+35 −16
Original line number Diff line number Diff line
@@ -3501,36 +3501,47 @@ static inline void set_tg_cfs_propagate(struct cfs_rq *cfs_rq) {} 
static inline int

update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)

{

	unsigned long removed_load = 0, removed_util = 0;

	struct sched_avg *sa = &cfs_rq->avg;

	int decayed, removed_load = 0, removed_util = 0;

	int decayed = 0;



	if (atomic_long_read(&cfs_rq->removed_load_avg)) {

		s64 r = atomic_long_xchg(&cfs_rq->removed_load_avg, 0);

	if (cfs_rq->removed.nr) {

		unsigned long r;



		raw_spin_lock(&cfs_rq->removed.lock);

		swap(cfs_rq->removed.util_avg, removed_util);

		swap(cfs_rq->removed.load_avg, removed_load);

		cfs_rq->removed.nr = 0;

		raw_spin_unlock(&cfs_rq->removed.lock);



		/*

		 * The LOAD_AVG_MAX for _sum is a slight over-estimate,

		 * which is safe due to sub_positive() clipping at 0.

		 */

		r = removed_load;

		sub_positive(&sa->load_avg, r);

		sub_positive(&sa->load_sum, r * LOAD_AVG_MAX);

		removed_load = 1;

		set_tg_cfs_propagate(cfs_rq);

	}



	if (atomic_long_read(&cfs_rq->removed_util_avg)) {

		long r = atomic_long_xchg(&cfs_rq->removed_util_avg, 0);

		r = removed_util;

		sub_positive(&sa->util_avg, r);

		sub_positive(&sa->util_sum, r * LOAD_AVG_MAX);

		removed_util = 1;



		set_tg_cfs_propagate(cfs_rq);



		decayed = 1;

	}



	decayed = __update_load_avg_cfs_rq(now, cpu_of(rq_of(cfs_rq)), cfs_rq);

	decayed |= __update_load_avg_cfs_rq(now, cpu_of(rq_of(cfs_rq)), cfs_rq);



#ifndef CONFIG_64BIT

	smp_wmb();

	cfs_rq->load_last_update_time_copy = sa->last_update_time;

#endif



	if (decayed || removed_util)

	if (decayed)

		cfs_rq_util_change(cfs_rq);



	return decayed || removed_load;

	return decayed;

}



/**
@@ -3645,6 +3656,7 @@ void sync_entity_load_avg(struct sched_entity *se) 
void remove_entity_load_avg(struct sched_entity *se)

{

	struct cfs_rq *cfs_rq = cfs_rq_of(se);

	unsigned long flags;



	/*

	 * tasks cannot exit without having gone through wake_up_new_task() ->
@@ -3654,11 +3666,19 @@ void remove_entity_load_avg(struct sched_entity *se) 
	 * Similarly for groups, they will have passed through

	 * post_init_entity_util_avg() before unregister_sched_fair_group()

	 * calls this.

	 *

	 * XXX in case entity_is_task(se) && task_of(se)->on_rq == MIGRATING

	 * we could actually get the right time, since we're called with

	 * rq->lock held, see detach_task().

	 */



	sync_entity_load_avg(se);

	atomic_long_add(se->avg.load_avg, &cfs_rq->removed_load_avg);

	atomic_long_add(se->avg.util_avg, &cfs_rq->removed_util_avg);



	raw_spin_lock_irqsave(&cfs_rq->removed.lock, flags);

	++cfs_rq->removed.nr;

	cfs_rq->removed.util_avg	+= se->avg.util_avg;

	cfs_rq->removed.load_avg	+= se->avg.load_avg;

	raw_spin_unlock_irqrestore(&cfs_rq->removed.lock, flags);

}



static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq)
@@ -9449,8 +9469,7 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) 
#ifdef CONFIG_FAIR_GROUP_SCHED

	cfs_rq->propagate_avg = 0;

#endif

	atomic_long_set(&cfs_rq->removed_load_avg, 0);

	atomic_long_set(&cfs_rq->removed_util_avg, 0);

	raw_spin_lock_init(&cfs_rq->removed.lock);

#endif

}

kernel/sched/sched.h

+9 −4
Original line number Diff line number Diff line
@@ -445,14 +445,19 @@ struct cfs_rq { 
	struct sched_avg avg;

	u64 runnable_load_sum;

	unsigned long runnable_load_avg;

#ifndef CONFIG_64BIT

	u64 load_last_update_time_copy;

#endif

#ifdef CONFIG_FAIR_GROUP_SCHED

	unsigned long tg_load_avg_contrib;

	unsigned long propagate_avg;

#endif

	atomic_long_t removed_load_avg, removed_util_avg;

#ifndef CONFIG_64BIT

	u64 load_last_update_time_copy;

#endif

	struct {

		raw_spinlock_t	lock ____cacheline_aligned;

		int		nr;

		unsigned long	load_avg;

		unsigned long	util_avg;

	} removed;



#ifdef CONFIG_FAIR_GROUP_SCHED

	/*

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