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Commit 9ee474f5 authored by Paul Turner's avatar Paul Turner Committed by Ingo Molnar
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sched: Maintain the load contribution of blocked entities 



We are currently maintaining:

  runnable_load(cfs_rq) = \Sum task_load(t)

For all running children t of cfs_rq.  While this can be naturally updated for
tasks in a runnable state (as they are scheduled); this does not account for
the load contributed by blocked task entities.

This can be solved by introducing a separate accounting for blocked load:

  blocked_load(cfs_rq) = \Sum runnable(b) * weight(b)

Obviously we do not want to iterate over all blocked entities to account for
their decay, we instead observe that:

  runnable_load(t) = \Sum p_i*y^i

and that to account for an additional idle period we only need to compute:

  y*runnable_load(t).

This means that we can compute all blocked entities at once by evaluating:

  blocked_load(cfs_rq)` = y * blocked_load(cfs_rq)

Finally we maintain a decay counter so that when a sleeping entity re-awakens
we can determine how much of its load should be removed from the blocked sum.

Signed-off-by: default avatarPaul Turner <pjt@google.com>
Reviewed-by: default avatarBen Segall <bsegall@google.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120823141506.585389902@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 2dac754e

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1103,6 +1103,7 @@ struct sched_avg { 
	 */

	u32 runnable_avg_sum, runnable_avg_period;

	u64 last_runnable_update;

	s64 decay_count;

	unsigned long load_avg_contrib;

};

kernel/sched/core.c

+0 −1
Original line number Diff line number Diff line
@@ -1528,7 +1528,6 @@ static void __sched_fork(struct task_struct *p) 
	p->se.avg.runnable_avg_period = 0;

	p->se.avg.runnable_avg_sum = 0;

#endif



#ifdef CONFIG_SCHEDSTATS

	memset(&p->se.statistics, 0, sizeof(p->se.statistics));

#endif

kernel/sched/debug.c

+3 −0
Original line number Diff line number Diff line
@@ -95,6 +95,7 @@ static void print_cfs_group_stats(struct seq_file *m, int cpu, struct task_group 
	P(se->avg.runnable_avg_sum);

	P(se->avg.runnable_avg_period);

	P(se->avg.load_avg_contrib);

	P(se->avg.decay_count);

#endif

#undef PN

#undef P
@@ -227,6 +228,8 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) 
			atomic_read(&cfs_rq->tg->load_weight));

	SEQ_printf(m, "  .%-30s: %lld\n", "runnable_load_avg",

			cfs_rq->runnable_load_avg);

	SEQ_printf(m, "  .%-30s: %lld\n", "blocked_load_avg",

			cfs_rq->blocked_load_avg);

#endif



	print_cfs_group_stats(m, cpu, cfs_rq->tg);

kernel/sched/fair.c

+115 −13
Original line number Diff line number Diff line
@@ -259,6 +259,8 @@ static inline struct cfs_rq *group_cfs_rq(struct sched_entity *grp) 
	return grp->my_q;

}



static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq);



static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq)

{

	if (!cfs_rq->on_list) {
@@ -278,6 +280,8 @@ static inline void list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq) 
		}



		cfs_rq->on_list = 1;

		/* We should have no load, but we need to update last_decay. */

		update_cfs_rq_blocked_load(cfs_rq);

	}

}
@@ -1081,6 +1085,20 @@ static __always_inline int __update_entity_runnable_avg(u64 now, 
	return decayed;

}



/* Synchronize an entity's decay with its parenting cfs_rq.*/

static inline void __synchronize_entity_decay(struct sched_entity *se)

{

	struct cfs_rq *cfs_rq = cfs_rq_of(se);

	u64 decays = atomic64_read(&cfs_rq->decay_counter);



	decays -= se->avg.decay_count;

	if (!decays)

		return;



	se->avg.load_avg_contrib = decay_load(se->avg.load_avg_contrib, decays);

	se->avg.decay_count = 0;

}



/* Compute the current contribution to load_avg by se, return any delta */

static long __update_entity_load_avg_contrib(struct sched_entity *se)

{
@@ -1096,8 +1114,18 @@ static long __update_entity_load_avg_contrib(struct sched_entity *se) 
	return se->avg.load_avg_contrib - old_contrib;

}



static inline void subtract_blocked_load_contrib(struct cfs_rq *cfs_rq,

						 long load_contrib)

{

	if (likely(load_contrib < cfs_rq->blocked_load_avg))

		cfs_rq->blocked_load_avg -= load_contrib;

	else

		cfs_rq->blocked_load_avg = 0;

}



/* Update a sched_entity's runnable average */

static inline void update_entity_load_avg(struct sched_entity *se)

static inline void update_entity_load_avg(struct sched_entity *se,

					  int update_cfs_rq)

{

	struct cfs_rq *cfs_rq = cfs_rq_of(se);

	long contrib_delta;
@@ -1107,8 +1135,34 @@ static inline void update_entity_load_avg(struct sched_entity *se) 
		return;



	contrib_delta = __update_entity_load_avg_contrib(se);



	if (!update_cfs_rq)

		return;



	if (se->on_rq)

		cfs_rq->runnable_load_avg += contrib_delta;

	else

		subtract_blocked_load_contrib(cfs_rq, -contrib_delta);

}



/*

 * Decay the load contributed by all blocked children and account this so that

 * their contribution may appropriately discounted when they wake up.

 */

static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq)

{

	u64 now = rq_of(cfs_rq)->clock_task >> 20;

	u64 decays;



	decays = now - cfs_rq->last_decay;

	if (!decays)

		return;



	cfs_rq->blocked_load_avg = decay_load(cfs_rq->blocked_load_avg,

					      decays);

	atomic64_add(decays, &cfs_rq->decay_counter);



	cfs_rq->last_decay = now;

}



static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
@@ -1118,26 +1172,53 @@ static inline void update_rq_runnable_avg(struct rq *rq, int runnable) 


/* Add the load generated by se into cfs_rq's child load-average */

static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,

						  struct sched_entity *se)

						  struct sched_entity *se,

						  int wakeup)

{

	update_entity_load_avg(se);

	/* we track migrations using entity decay_count == 0 */

	if (unlikely(!se->avg.decay_count)) {

		se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task;

		wakeup = 0;

	} else {

		__synchronize_entity_decay(se);

	}



	if (wakeup)

		subtract_blocked_load_contrib(cfs_rq, se->avg.load_avg_contrib);



	update_entity_load_avg(se, 0);

	cfs_rq->runnable_load_avg += se->avg.load_avg_contrib;

	update_cfs_rq_blocked_load(cfs_rq);

}



/* Remove se's load from this cfs_rq child load-average */

/*

 * Remove se's load from this cfs_rq child load-average, if the entity is

 * transitioning to a blocked state we track its projected decay using

 * blocked_load_avg.

 */

static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,

						  struct sched_entity *se)

						  struct sched_entity *se,

						  int sleep)

{

	update_entity_load_avg(se);

	update_entity_load_avg(se, 1);



	cfs_rq->runnable_load_avg -= se->avg.load_avg_contrib;

	if (sleep) {

		cfs_rq->blocked_load_avg += se->avg.load_avg_contrib;

		se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);

	} /* migrations, e.g. sleep=0 leave decay_count == 0 */

}

#else

static inline void update_entity_load_avg(struct sched_entity *se) {}

static inline void update_entity_load_avg(struct sched_entity *se,

					  int update_cfs_rq) {}

static inline void update_rq_runnable_avg(struct rq *rq, int runnable) {}

static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,

						  struct sched_entity *se) {}

					   struct sched_entity *se,

					   int wakeup) {}

static inline void dequeue_entity_load_avg(struct cfs_rq *cfs_rq,

						  struct sched_entity *se) {}

					   struct sched_entity *se,

					   int sleep) {}

static inline void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq) {}

#endif



static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -1266,7 +1347,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 
	 */

	update_curr(cfs_rq);

	update_cfs_load(cfs_rq, 0);

	enqueue_entity_load_avg(cfs_rq, se);

	enqueue_entity_load_avg(cfs_rq, se, flags & ENQUEUE_WAKEUP);

	account_entity_enqueue(cfs_rq, se);

	update_cfs_shares(cfs_rq);
@@ -1341,7 +1422,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 
	 * Update run-time statistics of the 'current'.

	 */

	update_curr(cfs_rq);

	dequeue_entity_load_avg(cfs_rq, se);

	dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);



	update_stats_dequeue(cfs_rq, se);

	if (flags & DEQUEUE_SLEEP) {
@@ -1512,7 +1593,7 @@ static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev) 
		/* Put 'current' back into the tree. */

		__enqueue_entity(cfs_rq, prev);

		/* in !on_rq case, update occurred at dequeue */

		update_entity_load_avg(prev);

		update_entity_load_avg(prev, 1);

	}

	cfs_rq->curr = NULL;

}
@@ -1528,7 +1609,8 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued) 
	/*

	 * Ensure that runnable average is periodically updated.

	 */

	update_entity_load_avg(curr);

	update_entity_load_avg(curr, 1);

	update_cfs_rq_blocked_load(cfs_rq);



	/*

	 * Update share accounting for long-running entities.
@@ -2387,6 +2469,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) 


		update_cfs_load(cfs_rq, 0);

		update_cfs_shares(cfs_rq);

		update_entity_load_avg(se, 1);

	}



	if (!se) {
@@ -2448,6 +2531,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) 


		update_cfs_load(cfs_rq, 0);

		update_cfs_shares(cfs_rq);

		update_entity_load_avg(se, 1);

	}



	if (!se) {
@@ -3498,6 +3582,7 @@ static int update_shares_cpu(struct task_group *tg, int cpu) 


	update_rq_clock(rq);

	update_cfs_load(cfs_rq, 1);

	update_cfs_rq_blocked_load(cfs_rq);



	/*

	 * We need to update shares after updating tg->load_weight in
@@ -5232,6 +5317,20 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p) 
		place_entity(cfs_rq, se, 0);

		se->vruntime -= cfs_rq->min_vruntime;

	}



#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)

	/*

	* Remove our load from contribution when we leave sched_fair

	* and ensure we don't carry in an old decay_count if we

	* switch back.

	*/

	if (p->se.avg.decay_count) {

		struct cfs_rq *cfs_rq = cfs_rq_of(&p->se);

		__synchronize_entity_decay(&p->se);

		subtract_blocked_load_contrib(cfs_rq,

				p->se.avg.load_avg_contrib);

	}

#endif

}



/*
@@ -5278,6 +5377,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) 
#ifndef CONFIG_64BIT

	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;

#endif

#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)

	atomic64_set(&cfs_rq->decay_counter, 1);

#endif

}



#ifdef CONFIG_FAIR_GROUP_SCHED

kernel/sched/sched.h

+3 −1
Original line number Diff line number Diff line
@@ -229,7 +229,9 @@ struct cfs_rq { 
	 * This allows for the description of both thread and group usage (in

	 * the FAIR_GROUP_SCHED case).

	 */

	u64 runnable_load_avg;

	u64 runnable_load_avg, blocked_load_avg;

	atomic64_t decay_counter;

	u64 last_decay;

#endif

#ifdef CONFIG_FAIR_GROUP_SCHED

	struct rq *rq;	/* cpu runqueue to which this cfs_rq is attached */