[PATCH v3 4/5] sched: sync a se with its cfs_rq when switching sched class to fair class
From: byungchul . park
Date: Wed Aug 19 2015 - 02:48:11 EST
From: Byungchul Park <byungchul.park@xxxxxxx>
we have to sync a se with its cfs_rq, when switching sched class to
fair class.
current code does not sync it because the se average load won't be
valid any more if it has been detached for a long time. however the
se's average load would be valid just after being detached from cfs_rq,
so we need to sync it in that case, e.g. priority inheritance.
to solve the problem that a se average load becomes more useless over
time, this patch decays its average load even for the duration that
the se has been detached, when it gets attached to the cfs_rq.
Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
kernel/sched/fair.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1be042a..3419f6c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2711,6 +2711,17 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
+ /*
+ * in case of migration and cgroup-change, more care should be taken
+ * because se's cfs_rq was changed, that means calling __update_load_avg
+ * with new cfs_rq->avg.last_update_time is meaningless. so we skip the
+ * update here. we have to update it with prev cfs_rq just before changing
+ * se's cfs_rq, and get here soon.
+ */
+ if (se->avg.last_update_time)
+ __update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
+ &se->avg, 0, 0, NULL);
+
se->avg.last_update_time = cfs_rq->avg.last_update_time;
cfs_rq->avg.load_avg += se->avg.load_avg;
cfs_rq->avg.load_sum += se->avg.load_sum;
@@ -7948,6 +7959,11 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
se->depth = se->parent ? se->parent->depth + 1 : 0;
#endif
+#ifdef CONFIG_SMP
+ /* synchronize task with its cfs_rq */
+ attach_entity_load_avg(cfs_rq_of(&p->se), &p->se);
+#endif
+
if (!task_on_rq_queued(p)) {
/*
@@ -8049,6 +8065,10 @@ static void task_move_group_fair(struct task_struct *p, int queued)
detach_entity_load_avg(cfs_rq, se);
#endif
set_task_rq(p, task_cpu(p));
+
+ /* tell se's cfs_rq has been changed */
+ p->se.avg.last_update_time = 0;
+
se->depth = se->parent ? se->parent->depth + 1 : 0;
cfs_rq = cfs_rq_of(se);
if (!queued)
--
1.7.9.5
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