From: Kuyo Chang <kuyo.chang@mediatek.com>
To: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, "Mel Gorman" <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Matthias Brugger <matthias.bgg@gmail.com>
Cc: <wsd_upstream@mediatek.com>, kuyo chang <kuyo.chang@mediatek.com>,
"Ingo Molnar" <mingo@kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-mediatek@lists.infradead.org>
Subject: [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method
Date: Thu, 14 Apr 2022 17:02:20 +0800 [thread overview]
Message-ID: <20220414090229.342-1-kuyo.chang@mediatek.com> (raw)
From: kuyo chang <kuyo.chang@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.
Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq and its se")
Signed-off-by: kuyo chang <kuyo.chang@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.
v2->v3:
(1)Rename Subject.
(1)Add fix tag.
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
next reply other threads:[~2022-04-14 9:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 9:02 Kuyo Chang [this message]
2022-04-14 14:44 ` [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method Peter Zijlstra
2022-04-15 3:56 ` Kuyo Chang
2022-04-19 19:35 ` [tip: sched/urgent] sched/pelt: Fix attach_entity_load_avg() corner case tip-bot2 for kuyo chang
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