Vincent reported that when a new task is moved into a new cgroup it
gets attached twice to the load tracking.
sched_move_task()
task_move_group_fair()
detach_task_cfs_rq()
set_task_rq()
attach_task_cfs_rq()
attach_entity_load_avg()
se->avg.last_load_update = cfs_rq->avg.last_load_update // == 0
enqueue_entity()
enqueue_entity_load_avg()
update_cfs_rq_load_avg()
now = clock()
__update_load_avg(&cfs_rq->avg)
cfs_rq->avg.last_load_update = now
// ages load/util for: now - 0, load/util -> 0
if (migrated)
attach_entity_load_avg()
se->avg.last_load_update = cfs_rq->avg.last_load_update; // now != 0
The problem is that we don't update cfs_rq load_avg before all
entity attach/detach operations. Only enqueue and migrate_task do
this.
By fixing this, the above will not happen, because the
sched_move_task() attach will have updated cfs_rq's last_load_update
time before attach, and in turn the attach will have set the entity's
last_load_update stamp.
Note that there is a further problem with sched_move_task() calling
detach on a task that hasn't yet been attached; this will be taken
care of in a subsequent patch.
Cc: Yuyang Du <[email protected]>
Reported-by: Vincent Guittot <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
kernel/sched/fair.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8366,6 +8366,7 @@ static void detach_task_cfs_rq(struct ta
{
struct sched_entity *se = &p->se;
struct cfs_rq *cfs_rq = cfs_rq_of(se);
+ u64 now = cfs_rq_clock_task(cfs_rq);
if (!vruntime_normalized(p)) {
/*
@@ -8377,6 +8378,7 @@ static void detach_task_cfs_rq(struct ta
}
/* Catch up with the cfs_rq and remove our load when we leave */
+ update_cfs_rq_load_avg(now, cfs_rq, false);
detach_entity_load_avg(cfs_rq, se);
}
@@ -8384,6 +8386,7 @@ static void attach_task_cfs_rq(struct ta
{
struct sched_entity *se = &p->se;
struct cfs_rq *cfs_rq = cfs_rq_of(se);
+ u64 now = cfs_rq_clock_task(cfs_rq);
#ifdef CONFIG_FAIR_GROUP_SCHED
/*
@@ -8394,6 +8397,7 @@ static void attach_task_cfs_rq(struct ta
#endif
/* Synchronize task with its cfs_rq */
+ update_cfs_rq_load_avg(now, cfs_rq, false);
attach_entity_load_avg(cfs_rq, se);
if (!vruntime_normalized(p))
