[PATCH 02/15] sched: set initial load avg of new forked task

[Alex Shi]

New task has no runnable sum at its first runnable time, so its
runnable load is zero. That makes burst forking balancing just select
few idle cpus to assign tasks if we engage runnable load in balancing.

Set initial load avg of new forked task as its load weight to resolve
this issue.

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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1743746..93a7590 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1648,6 +1648,8 @@ void sched_fork(struct task_struct *p)
 		p->sched_reset_on_fork = 0;
 	}
 
+	p->se.avg.load_avg_contrib = p->se.load.weight;
+
 	if (!rt_prio(p->prio))
 		p->sched_class = &fair_sched_class;
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 81fa536..cae5134 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

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