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Commit e33078ba authored by Paul Turner's avatar Paul Turner Committed by Ingo Molnar
Browse files

sched: Fix update_cfs_load() synchronization 



Using cfs_rq->nr_running is not sufficient to synchronize update_cfs_load with
the put path since nr_running accounting occurs at deactivation.

It's also not safe to make the removal decision based on load_avg as this fails
with both high periods and low shares.  Resolve this by clipping history after
4 periods without activity.

Note: the above will always occur from update_shares() since in the
last-task-sleep-case that task will still be cfs_rq->curr when update_cfs_load
is called.

Signed-off-by: default avatarPaul Turner <pjt@google.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20101115234937.933428187@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent f0d7442a

kernel/sched.c

+1 −1
Original line number Diff line number Diff line
@@ -355,7 +355,7 @@ struct cfs_rq { 


	u64 load_avg;

	u64 load_period;

	u64 load_stamp;

	u64 load_stamp, load_last;



	unsigned long load_contribution;

#endif

kernel/sched_fair.c

+21 −12
Original line number Diff line number Diff line
@@ -674,10 +674,11 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se) 
}



#if defined CONFIG_SMP && defined CONFIG_FAIR_GROUP_SCHED

static void update_cfs_load(struct cfs_rq *cfs_rq, int lb)

static void update_cfs_load(struct cfs_rq *cfs_rq)

{

	u64 period = sched_avg_period();

	u64 now, delta;

	unsigned long load = cfs_rq->load.weight;



	if (!cfs_rq)

		return;
@@ -685,9 +686,19 @@ static void update_cfs_load(struct cfs_rq *cfs_rq, int lb) 
	now = rq_of(cfs_rq)->clock;

	delta = now - cfs_rq->load_stamp;



	/* truncate load history at 4 idle periods */

	if (cfs_rq->load_stamp > cfs_rq->load_last &&

	    now - cfs_rq->load_last > 4 * period) {

		cfs_rq->load_period = 0;

		cfs_rq->load_avg = 0;

	}



	cfs_rq->load_stamp = now;

	cfs_rq->load_period += delta;

	cfs_rq->load_avg += delta * cfs_rq->load.weight;

	if (load) {

		cfs_rq->load_last = now;

		cfs_rq->load_avg += delta * load;

	}



	while (cfs_rq->load_period > period) {

		/*
@@ -700,11 +711,9 @@ static void update_cfs_load(struct cfs_rq *cfs_rq, int lb) 
		cfs_rq->load_avg /= 2;

	}



	if (lb && !cfs_rq->nr_running) {

		if (cfs_rq->load_avg < (period / 8))

	if (!cfs_rq->curr && !cfs_rq->nr_running && !cfs_rq->load_avg)

		list_del_leaf_cfs_rq(cfs_rq);

}

}



static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,

			    unsigned long weight)
@@ -750,7 +759,7 @@ static void update_cfs_shares(struct cfs_rq *cfs_rq, long weight_delta) 
	reweight_entity(cfs_rq_of(se), se, shares);

}

#else /* CONFIG_FAIR_GROUP_SCHED */

static inline void update_cfs_load(struct cfs_rq *cfs_rq, int lb)

static inline void update_cfs_load(struct cfs_rq *cfs_rq)

{

}
@@ -880,7 +889,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 
	 * Update run-time statistics of the 'current'.

	 */

	update_curr(cfs_rq);

	update_cfs_load(cfs_rq, 0);

	update_cfs_load(cfs_rq);

	update_cfs_shares(cfs_rq, se->load.weight);

	account_entity_enqueue(cfs_rq, se);
@@ -941,7 +950,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) 
	if (se != cfs_rq->curr)

		__dequeue_entity(cfs_rq, se);

	se->on_rq = 0;

	update_cfs_load(cfs_rq, 0);

	update_cfs_load(cfs_rq);

	account_entity_dequeue(cfs_rq, se);

	update_min_vruntime(cfs_rq);

	update_cfs_shares(cfs_rq, 0);
@@ -1176,7 +1185,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) 
	for_each_sched_entity(se) {

		struct cfs_rq *cfs_rq = cfs_rq_of(se);



		update_cfs_load(cfs_rq, 0);

		update_cfs_load(cfs_rq);

		update_cfs_shares(cfs_rq, 0);

	}
@@ -1206,7 +1215,7 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) 
	for_each_sched_entity(se) {

		struct cfs_rq *cfs_rq = cfs_rq_of(se);



		update_cfs_load(cfs_rq, 0);

		update_cfs_load(cfs_rq);

		update_cfs_shares(cfs_rq, 0);

	}
@@ -2023,7 +2032,7 @@ static int tg_shares_up(struct task_group *tg, int cpu) 
	raw_spin_lock_irqsave(&rq->lock, flags);



	update_rq_clock(rq);

	update_cfs_load(cfs_rq, 1);

	update_cfs_load(cfs_rq);



	load_avg = div64_u64(cfs_rq->load_avg, cfs_rq->load_period+1);

	load_avg -= cfs_rq->load_contribution;