Commit 6d4d2246 authored by Vincent Guittot's avatar Vincent Guittot Committed by Ingo Molnar
Browse files

sched/fair: Reorder enqueue/dequeue_task_fair path 



The walk through the cgroup hierarchy during the enqueue/dequeue of a task
is split in 2 distinct parts for throttled cfs_rq without any added value
but making code less readable.

Change the code ordering such that everything related to a cfs_rq
(throttled or not) will be done in the same loop.

In addition, the same steps ordering is used when updating a cfs_rq:

 - update_load_avg
 - update_cfs_group
 - update *h_nr_running

This reordering enables the use of h_nr_running in PELT algorithm.

No functional and performance changes are expected and have been noticed
during tests.

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatar"Dietmar Eggemann <dietmar.eggemann@arm.com&gt;">
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Hillf Danton <hdanton@sina.com>
Link: https://lore.kernel.org/r/20200224095223.13361-5-mgorman@techsingularity.net
parent b2b2042b

kernel/sched/fair.c

+20 −22
Original line number Diff line number Diff line
@@ -5260,32 +5260,31 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) 
		cfs_rq = cfs_rq_of(se);

		enqueue_entity(cfs_rq, se, flags);



		/*

		 * end evaluation on encountering a throttled cfs_rq

		 *

		 * note: in the case of encountering a throttled cfs_rq we will

		 * post the final h_nr_running increment below.

		 */

		if (cfs_rq_throttled(cfs_rq))

			break;

		cfs_rq->h_nr_running++;

		cfs_rq->idle_h_nr_running += idle_h_nr_running;



		/* end evaluation on encountering a throttled cfs_rq */

		if (cfs_rq_throttled(cfs_rq))

			goto enqueue_throttle;



		flags = ENQUEUE_WAKEUP;

	}



	for_each_sched_entity(se) {

		cfs_rq = cfs_rq_of(se);

		cfs_rq->h_nr_running++;

		cfs_rq->idle_h_nr_running += idle_h_nr_running;



		/* end evaluation on encountering a throttled cfs_rq */

		if (cfs_rq_throttled(cfs_rq))

			break;

			goto enqueue_throttle;



		update_load_avg(cfs_rq, se, UPDATE_TG);

		update_cfs_group(se);



		cfs_rq->h_nr_running++;

		cfs_rq->idle_h_nr_running += idle_h_nr_running;

	}



enqueue_throttle:

	if (!se) {

		add_nr_running(rq, 1);

		/*
@@ -5346,17 +5345,13 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) 
		cfs_rq = cfs_rq_of(se);

		dequeue_entity(cfs_rq, se, flags);



		/*

		 * end evaluation on encountering a throttled cfs_rq

		 *

		 * note: in the case of encountering a throttled cfs_rq we will

		 * post the final h_nr_running decrement below.

		*/

		if (cfs_rq_throttled(cfs_rq))

			break;

		cfs_rq->h_nr_running--;

		cfs_rq->idle_h_nr_running -= idle_h_nr_running;



		/* end evaluation on encountering a throttled cfs_rq */

		if (cfs_rq_throttled(cfs_rq))

			goto dequeue_throttle;



		/* Don't dequeue parent if it has other entities besides us */

		if (cfs_rq->load.weight) {

			/* Avoid re-evaluating load for this entity: */
@@ -5374,16 +5369,19 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) 


	for_each_sched_entity(se) {

		cfs_rq = cfs_rq_of(se);

		cfs_rq->h_nr_running--;

		cfs_rq->idle_h_nr_running -= idle_h_nr_running;



		/* end evaluation on encountering a throttled cfs_rq */

		if (cfs_rq_throttled(cfs_rq))

			break;

			goto dequeue_throttle;



		update_load_avg(cfs_rq, se, UPDATE_TG);

		update_cfs_group(se);



		cfs_rq->h_nr_running--;

		cfs_rq->idle_h_nr_running -= idle_h_nr_running;

	}



dequeue_throttle:

	if (!se)

		sub_nr_running(rq, 1);

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