[PATCH] sched: Initialize the vruntime of a new task when it is first enqueued

[Zhang Qiao]

When create a new task, we initialize vruntime of the new task
at sched_cgroup_fork(). However, the timing of executing this
action is too early and may not be accurate.

Because it use current cpu to init the vruntime, but the new
task actually runs on the cpu which be assigned at wake_up_new_task().

To optimize this case, we pass ENQUEUE_INITIAL flag to
activate_task() in wake_up_new_task(), in this way,
when place_entity is called in enqueue_entity(), the
vruntime of the new task will be initialized. At the same
time, place_entity in task_fork_fair() is useless, remove it.

Signed-off-by: Zhang Qiao <zhangqiao22@xxxxxxxxxx>
---
 kernel/sched/core.c |  2 +-
 kernel/sched/fair.c | 16 ----------------
 2 files changed, 1 insertion(+), 17 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bcf2c4cc0522..b4ff595a2dc8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4897,7 +4897,7 @@ void wake_up_new_task(struct task_struct *p)
 	update_rq_clock(rq);
 	post_init_entity_util_avg(p);
 
-	activate_task(rq, p, ENQUEUE_NOCLOCK);
+	activate_task(rq, p, ENQUEUE_NOCLOCK | ENQUEUE_INITIAL);
 	trace_sched_wakeup_new(p);
 	wakeup_preempt(rq, p, WF_FORK);
 #ifdef CONFIG_SMP
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index efce2d36a783..bb5f376fd51e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12702,23 +12702,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
  */
 static void task_fork_fair(struct task_struct *p)
 {
-	struct sched_entity *se = &p->se, *curr;
-	struct cfs_rq *cfs_rq;
-	struct rq *rq = this_rq();
-	struct rq_flags rf;
-
-	rq_lock(rq, &rf);
-
 	set_task_max_allowed_capacity(p);
-
-	cfs_rq = task_cfs_rq(current);
-	curr = cfs_rq->curr;
-	if (curr) {
-		update_rq_clock(rq);
-		update_curr(cfs_rq);
-	}
-	place_entity(cfs_rq, se, ENQUEUE_INITIAL);
-	rq_unlock(rq, &rf);
 }
 
 /*
-- 
2.18.0.huawei.25