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Subject[PATCH 04/12] sched/fair: reorder enqueue/dequeue_task_fair path
Date
From: Vincent Guittot <vincent.guittot@linaro.org>

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

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

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
kernel/sched/fair.c | 42 ++++++++++++++++++++----------------------
1 file changed, 20 insertions(+), 22 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6c866fb2129c..4395951b1530 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5261,32 +5261,31 @@ 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);
/*
@@ -5347,17 +5346,13 @@ 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: */
@@ -5375,16 +5370,19 @@ 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);

--
2.16.4
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