[PATCH v4 2/6] sched: set initial value of runnable avg for new forked task

Alex Shi
2013-04-27T05:27:24Z

We need initialize the se.avg.{decay_count, load_avg_contrib} for a
new forked task.
Otherwise random values of above variables cause mess when do new task
enqueue:
enqueue_task_fair
enqueue_entity
enqueue_entity_load_avg

and make forking balancing imbalance since incorrect load_avg_contrib.

set avg.decay_count = 0, and avg.load_avg_contrib = se->load.weight to
resolve such issues.

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
kernel/sched/core.c | 6 ++++++
kernel/sched/fair.c | 4 ++++
2 files changed, 10 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 86e87f1..e0c003a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1564,6 +1564,7 @@ static void __sched_fork(struct task_struct *p)
#ifdef CONFIG_SMP
p->se.avg.runnable_avg_period = 0;
p->se.avg.runnable_avg_sum = 0;
+ p->se.avg.decay_count = 0;
#endif
#ifdef CONFIG_SCHEDSTATS
memset(&p->se.statistics, 0, sizeof(p->se.statistics));
@@ -1651,6 +1652,11 @@ void sched_fork(struct task_struct *p)
p->sched_reset_on_fork = 0;
}

+ /* New forked task assumed with full utilization */
+#if defined(CONFIG_SMP)
+ p->se.avg.load_avg_contrib = p->se.load.weight;
+#endif
+
if (!rt_prio(p->prio))
p->sched_class = &fair_sched_class;

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9bcb7f3..85ff367 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1509,6 +1509,10 @@ static inline void enqueue_entity_load_avg(struct cfs_rq *cfs_rq,
* We track migrations using entity decay_count <= 0, on a wake-up
* migration we use a negative decay count to track the remote decays
* accumulated while sleeping.
+ *
+ * When enqueue a new forked task, the se->avg.decay_count == 0, so
+ * we bypass update_entity_load_avg(), use avg.load_avg_contrib initial
+ * value: se->load.weight.
*/
if (unlikely(se->avg.decay_count <= 0)) {
se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task;
--
1.7.12