[PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method
Kuyo Chang
kuyo.chang at mediatek.com
Wed Apr 13 18:59:36 PDT 2022
From: kuyo chang <kuyo.chang at mediatek.com>
I meet the warning message at cfs_rq_is_decayed at below code.
SCHED_WARN_ON(cfs_rq->avg.load_avg ||
cfs_rq->avg.util_avg ||
cfs_rq->avg.runnable_avg)
Following is the calltrace.
Call trace:
__update_blocked_fair
update_blocked_averages
newidle_balance
pick_next_task_fair
__schedule
schedule
pipe_read
vfs_read
ksys_read
After code analyzing and some debug messages, I found it exits a corner
case at attach_entity_load_avg which will cause load_sum is null but
load_avg is not.
Consider se_weight is 88761 according by sched_prio_to_weight table.
And assume the get_pelt_divider() is 47742, se->avg.load_avg is 1.
By the calculating for se->avg.load_sum as following will become zero
as following.
se->avg.load_sum =
div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
se->avg.load_sum = 1*47742/88761 = 0.
After enqueue_load_avg code as below.
cfs_rq->avg.load_avg += se->avg.load_avg;
cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
Then the load_sum for cfs_rq will be 1 while the load_sum for cfs_rq is 0.
So it will hit the warning message.
In order to fix the corner case, make sure the se->load_avg|sum is correct
before enqueue_load_avg.
After long time testing, the kernel warning was gone and the system runs
as well as before.
Signed-off-by: kuyo chang <kuyo.chang at mediatek.com>
---
v1->v2:
(1)Thanks for suggestion from Peter Zijlstra & Vincent Guittot.
(2)By suggestion from Vincent Guittot,
rework the se->load_sum calculation method for fix the corner case,
make sure the se->load_avg|sum is correct before enqueue_load_avg.
(3)Rework changlog.
kernel/sched/fair.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4bd299d67ab..159274482c4e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3829,10 +3829,12 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
se->avg.runnable_sum = se->avg.runnable_avg * divider;
- se->avg.load_sum = divider;
- if (se_weight(se)) {
+ se->avg.load_sum = se->avg.load_avg * divider;
+ if (se_weight(se) < se->avg.load_sum) {
se->avg.load_sum =
- div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se));
+ div_u64(se->avg.load_sum, se_weight(se));
+ } else {
+ se->avg.load_sum = 1;
}
enqueue_load_avg(cfs_rq, se);
--
2.18.0
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