Commit 09a43ace authored by Vincent Guittot's avatar Vincent Guittot Committed by Ingo Molnar
Browse files

sched/fair: Propagate load during synchronous attach/detach 



When a task moves from/to a cfs_rq, we set a flag which is then used to
propagate the change at parent level (sched_entity and cfs_rq) during
next update. If the cfs_rq is throttled, the flag will stay pending until
the cfs_rq is unthrottled.

For propagating the utilization, we copy the utilization of group cfs_rq to
the sched_entity.

For propagating the load, we have to take into account the load of the
whole task group in order to evaluate the load of the sched_entity.
Similarly to what was done before the rewrite of PELT, we add a correction
factor in case the task group's load is greater than its share so it will
contribute the same load of a task of equal weight.

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Cc: kernellwp@gmail.com
Cc: pjt@google.com
Cc: yuyang.du@intel.com
Link: http://lkml.kernel.org/r/1478598827-32372-5-git-send-email-vincent.guittot@linaro.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d31b1a66

kernel/sched/fair.c

+187 −1
Original line number Diff line number Diff line
@@ -2918,6 +2918,26 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, 
	return decayed;

}



/*

 * Signed add and clamp on underflow.

 *

 * Explicitly do a load-store to ensure the intermediate value never hits

 * memory. This allows lockless observations without ever seeing the negative

 * values.

 */

#define add_positive(_ptr, _val) do {                           \

	typeof(_ptr) ptr = (_ptr);                              \

	typeof(_val) val = (_val);                              \

	typeof(*ptr) res, var = READ_ONCE(*ptr);                \

								\

	res = var + val;                                        \

								\

	if (val < 0 && res > var)                               \

		res = 0;                                        \

								\

	WRITE_ONCE(*ptr, res);                                  \

} while (0)



#ifdef CONFIG_FAIR_GROUP_SCHED

/**

 * update_tg_load_avg - update the tg's load avg
@@ -2997,8 +3017,138 @@ void set_task_rq_fair(struct sched_entity *se, 
		se->avg.last_update_time = n_last_update_time;

	}

}



/* Take into account change of utilization of a child task group */

static inline void

update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se)

{

	struct cfs_rq *gcfs_rq = group_cfs_rq(se);

	long delta = gcfs_rq->avg.util_avg - se->avg.util_avg;



	/* Nothing to update */

	if (!delta)

		return;



	/* Set new sched_entity's utilization */

	se->avg.util_avg = gcfs_rq->avg.util_avg;

	se->avg.util_sum = se->avg.util_avg * LOAD_AVG_MAX;



	/* Update parent cfs_rq utilization */

	add_positive(&cfs_rq->avg.util_avg, delta);

	cfs_rq->avg.util_sum = cfs_rq->avg.util_avg * LOAD_AVG_MAX;

}



/* Take into account change of load of a child task group */

static inline void

update_tg_cfs_load(struct cfs_rq *cfs_rq, struct sched_entity *se)

{

	struct cfs_rq *gcfs_rq = group_cfs_rq(se);

	long delta, load = gcfs_rq->avg.load_avg;



	/*

	 * If the load of group cfs_rq is null, the load of the

	 * sched_entity will also be null so we can skip the formula

	 */

	if (load) {

		long tg_load;



		/* Get tg's load and ensure tg_load > 0 */

		tg_load = atomic_long_read(&gcfs_rq->tg->load_avg) + 1;



		/* Ensure tg_load >= load and updated with current load*/

		tg_load -= gcfs_rq->tg_load_avg_contrib;

		tg_load += load;



		/*

		 * We need to compute a correction term in the case that the

		 * task group is consuming more CPU than a task of equal

		 * weight. A task with a weight equals to tg->shares will have

		 * a load less or equal to scale_load_down(tg->shares).

		 * Similarly, the sched_entities that represent the task group

		 * at parent level, can't have a load higher than

		 * scale_load_down(tg->shares). And the Sum of sched_entities'

		 * load must be <= scale_load_down(tg->shares).

		 */

		if (tg_load > scale_load_down(gcfs_rq->tg->shares)) {

			/* scale gcfs_rq's load into tg's shares*/

			load *= scale_load_down(gcfs_rq->tg->shares);

			load /= tg_load;

		}

	}



	delta = load - se->avg.load_avg;



	/* Nothing to update */

	if (!delta)

		return;



	/* Set new sched_entity's load */

	se->avg.load_avg = load;

	se->avg.load_sum = se->avg.load_avg * LOAD_AVG_MAX;



	/* Update parent cfs_rq load */

	add_positive(&cfs_rq->avg.load_avg, delta);

	cfs_rq->avg.load_sum = cfs_rq->avg.load_avg * LOAD_AVG_MAX;



	/*

	 * If the sched_entity is already enqueued, we also have to update the

	 * runnable load avg.

	 */

	if (se->on_rq) {

		/* Update parent cfs_rq runnable_load_avg */

		add_positive(&cfs_rq->runnable_load_avg, delta);

		cfs_rq->runnable_load_sum = cfs_rq->runnable_load_avg * LOAD_AVG_MAX;

	}

}



static inline void set_tg_cfs_propagate(struct cfs_rq *cfs_rq)

{

	cfs_rq->propagate_avg = 1;

}



static inline int test_and_clear_tg_cfs_propagate(struct sched_entity *se)

{

	struct cfs_rq *cfs_rq = group_cfs_rq(se);



	if (!cfs_rq->propagate_avg)

		return 0;



	cfs_rq->propagate_avg = 0;

	return 1;

}



/* Update task and its cfs_rq load average */

static inline int propagate_entity_load_avg(struct sched_entity *se)

{

	struct cfs_rq *cfs_rq;



	if (entity_is_task(se))

		return 0;



	if (!test_and_clear_tg_cfs_propagate(se))

		return 0;



	cfs_rq = cfs_rq_of(se);



	set_tg_cfs_propagate(cfs_rq);



	update_tg_cfs_util(cfs_rq, se);

	update_tg_cfs_load(cfs_rq, se);



	return 1;

}



#else /* CONFIG_FAIR_GROUP_SCHED */



static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force) {}



static inline int propagate_entity_load_avg(struct sched_entity *se)

{

	return 0;

}



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



#endif /* CONFIG_FAIR_GROUP_SCHED */



static inline void cfs_rq_util_change(struct cfs_rq *cfs_rq)
@@ -3105,6 +3255,7 @@ static inline void update_load_avg(struct sched_entity *se, int flags) 
	u64 now = cfs_rq_clock_task(cfs_rq);

	struct rq *rq = rq_of(cfs_rq);

	int cpu = cpu_of(rq);

	int decayed;



	/*

	 * Track task load average for carrying it to new CPU after migrated, and
@@ -3116,7 +3267,10 @@ static inline void update_load_avg(struct sched_entity *se, int flags) 
			  cfs_rq->curr == se, NULL);

	}



	if (update_cfs_rq_load_avg(now, cfs_rq, true) && (flags & UPDATE_TG))

	decayed  = update_cfs_rq_load_avg(now, cfs_rq, true);

	decayed |= propagate_entity_load_avg(se);



	if (decayed && (flags & UPDATE_TG))

		update_tg_load_avg(cfs_rq, 0);

}
@@ -3135,6 +3289,7 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s 
	cfs_rq->avg.load_sum += se->avg.load_sum;

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

	cfs_rq->avg.util_sum += se->avg.util_sum;

	set_tg_cfs_propagate(cfs_rq);



	cfs_rq_util_change(cfs_rq);

}
@@ -3154,6 +3309,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s 
	sub_positive(&cfs_rq->avg.load_sum, se->avg.load_sum);

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

	sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);

	set_tg_cfs_propagate(cfs_rq);



	cfs_rq_util_change(cfs_rq);

}
@@ -8794,6 +8950,31 @@ static inline bool vruntime_normalized(struct task_struct *p) 
	return false;

}



#ifdef CONFIG_FAIR_GROUP_SCHED

/*

 * Propagate the changes of the sched_entity across the tg tree to make it

 * visible to the root

 */

static void propagate_entity_cfs_rq(struct sched_entity *se)

{

	struct cfs_rq *cfs_rq;



	/* Start to propagate at parent */

	se = se->parent;



	for_each_sched_entity(se) {

		cfs_rq = cfs_rq_of(se);



		if (cfs_rq_throttled(cfs_rq))

			break;



		update_load_avg(se, UPDATE_TG);

	}

}

#else

static void propagate_entity_cfs_rq(struct sched_entity *se) { }

#endif



static void detach_entity_cfs_rq(struct sched_entity *se)

{

	struct cfs_rq *cfs_rq = cfs_rq_of(se);
@@ -8802,6 +8983,7 @@ static void detach_entity_cfs_rq(struct sched_entity *se) 
	update_load_avg(se, 0);

	detach_entity_load_avg(cfs_rq, se);

	update_tg_load_avg(cfs_rq, false);

	propagate_entity_cfs_rq(se);

}



static void attach_entity_cfs_rq(struct sched_entity *se)
@@ -8820,6 +9002,7 @@ static void attach_entity_cfs_rq(struct sched_entity *se) 
	update_load_avg(se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);

	attach_entity_load_avg(cfs_rq, se);

	update_tg_load_avg(cfs_rq, false);

	propagate_entity_cfs_rq(se);

}



static void detach_task_cfs_rq(struct task_struct *p)
@@ -8898,6 +9081,9 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) 
	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;

#endif

#ifdef CONFIG_SMP

#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);

#endif

kernel/sched/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -404,6 +404,7 @@ struct cfs_rq { 
	unsigned long runnable_load_avg;

#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

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