[PATCH v4 5/5] sched: add two functions for att(det)aching a task to(from) a cfs_rq

byungchul.park
2015-08-20T11:22:44Z

From: Byungchul Park <byungchul.park@lge.com>

this patch introduces two functions for adjusting a task's vruntime
and the target cfs_rq's average load so that redundancy code doing
same things can be simplified. and it provides better readability.
switched_from_fair, switched_to_fair and task_move_group_fair can
use introduced functions and get simplified.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/sched/fair.c | 137 ++++++++++++++++++++++-----------------------------
1 file changed, 60 insertions(+), 77 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af6ad5f..53d0e30 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7918,21 +7918,47 @@ prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
check_preempt_curr(rq, p, 0);
}

-static void switched_from_fair(struct rq *rq, struct task_struct *p)
+static inline bool vruntime_normalized(struct task_struct *p)
{
+ int queued = task_on_rq_queued(p);
struct sched_entity *se = &p->se;
- struct cfs_rq *cfs_rq = cfs_rq_of(se);

/*
- * Ensure the task's vruntime is normalized, so that when it's
- * switched back to the fair class the enqueue_entity(.flags=0) will
- * do the right thing.
- *
* If it's queued, then the dequeue_entity(.flags=0) will already
- * have normalized the vruntime, if it's !queued, then only when
- * the task is sleeping will it still have non-normalized vruntime.
+ * have normalized the vruntime.
+ */
+ if (queued)
+ return true;
+
+ /*
+ * When !queued, vruntime of the task has usually NOT been normalized.
+ * But there are some cases where it has already been normalized:
+ *
+ * - A forked child which is waiting for being woken up by
+ * wake_up_new_task().
+ * - A task which has been woken up by try_to_wake_up() and
+ * waiting for actually being woken up by sched_ttwu_pending().
*/
- if (!task_on_rq_queued(p) && p->state != TASK_RUNNING) {
+ if (!se->sum_exec_runtime || p->state == TASK_WAKING)
+ return true;
+
+ /*
+ * If it's !queued, then only when the task is sleeping it has a
+ * non-normalized vruntime, that is, when the task is being migrated
+ * it has a normailized vruntime.
+ */
+ if (p->state == TASK_RUNNING)
+ return true;
+
+ return false;
+}
+
+static void detach_task_cfs_rq(struct task_struct *p)
+{
+ struct sched_entity *se = &p->se;
+ struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+ if (!vruntime_normalized(p)) {
/*
* Fix up our vruntime so that the current sleep doesn't
* cause 'unlimited' sleep bonus.
@@ -7945,9 +7971,10 @@ static void switched_from_fair(struct rq *rq, struct task_struct *p)
detach_entity_load_avg(cfs_rq, se);
}

-static void switched_to_fair(struct rq *rq, struct task_struct *p)
+static void attach_task_cfs_rq(struct task_struct *p)
{
struct sched_entity *se = &p->se;
+ struct cfs_rq *cfs_rq = cfs_rq_of(se);

#ifdef CONFIG_FAIR_GROUP_SCHED
/*
@@ -7958,33 +7985,32 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
#endif

/* Synchronize task with its cfs_rq */
- attach_entity_load_avg(cfs_rq_of(&p->se), &p->se);
+ attach_entity_load_avg(cfs_rq, se);

- if (!task_on_rq_queued(p)) {
+ if (!vruntime_normalized(p))
+ se->vruntime += cfs_rq->min_vruntime;
+}

+static void switched_from_fair(struct rq *rq, struct task_struct *p)
+{
+ detach_task_cfs_rq(p);
+}
+
+static void switched_to_fair(struct rq *rq, struct task_struct *p)
+{
+ attach_task_cfs_rq(p);
+
+ if (task_on_rq_queued(p)) {
/*
- * Ensure the task has a non-normalized vruntime when it is switched
- * back to the fair class with !queued, so that enqueue_entity() at
- * wake-up time will do the right thing.
- *
- * If it's queued, then the enqueue_entity(.flags=0) makes the task
- * has non-normalized vruntime, if it's !queued, then it still has
- * normalized vruntime.
+ * We were most likely switched from sched_rt, so
+ * kick off the schedule if running, otherwise just see
+ * if we can still preempt the current task.
*/
- if (p->state != TASK_RUNNING)
- se->vruntime += cfs_rq_of(se)->min_vruntime;
- return;
+ if (rq->curr == p)
+ resched_curr(rq);
+ else
+ check_preempt_curr(rq, p, 0);
}
-
- /*
- * We were most likely switched from sched_rt, so
- * kick off the schedule if running, otherwise just see
- * if we can still preempt the current task.
- */
- if (rq->curr == p)
- resched_curr(rq);
- else
- check_preempt_curr(rq, p, 0);
}

/* Account for a task changing its policy or group.
@@ -8021,55 +8047,12 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
#ifdef CONFIG_FAIR_GROUP_SCHED
static void task_move_group_fair(struct task_struct *p, int queued)
{
- struct sched_entity *se = &p->se;
- struct cfs_rq *cfs_rq;
-
- /*
- * If the task was not on the rq at the time of this cgroup movement
- * it must have been asleep, sleeping tasks keep their ->vruntime
- * absolute on their old rq until wakeup (needed for the fair sleeper
- * bonus in place_entity()).
- *
- * If it was on the rq, we've just 'preempted' it, which does convert
- * ->vruntime to a relative base.
- *
- * Make sure both cases convert their relative position when migrating
- * to another cgroup's rq. This does somewhat interfere with the
- * fair sleeper stuff for the first placement, but who cares.
- */
- /*
- * When !queued, vruntime of the task has usually NOT been normalized.
- * But there are some cases where it has already been normalized:
- *
- * - Moving a forked child which is waiting for being woken up by
- * wake_up_new_task().
- * - Moving a task which has been woken up by try_to_wake_up() and
- * waiting for actually being woken up by sched_ttwu_pending().
- *
- * To prevent boost or penalty in the new cfs_rq caused by delta
- * min_vruntime between the two cfs_rqs, we skip vruntime adjustment.
- */
- if (!queued && (!se->sum_exec_runtime || p->state == TASK_WAKING))
- queued = 1;
-
- cfs_rq = cfs_rq_of(se);
- if (!queued)
- se->vruntime -= cfs_rq->min_vruntime;
-
- /* Synchronize task with its prev cfs_rq */
- detach_entity_load_avg(cfs_rq, se);
+ detach_task_cfs_rq(p);
set_task_rq(p, task_cpu(p));

/* Tell se's cfs_rq has been changed -- migrated */
p->se.avg.last_update_time = 0;
-
- se->depth = se->parent ? se->parent->depth + 1 : 0;
- cfs_rq = cfs_rq_of(se);
- if (!queued)
- se->vruntime += cfs_rq->min_vruntime;
-
- /* Virtually synchronize task with its new cfs_rq */
- attach_entity_load_avg(cfs_rq, se);
+ attach_task_cfs_rq(p);
}

void free_fair_sched_group(struct task_group *tg)
--
1.7.9.5