From: "tip-bot2 for kuyo chang" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: kuyo chang <kuyo.chang@mediatek.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: sched/urgent] sched/pelt: Fix attach_entity_load_avg() corner case
Date: Tue, 19 Apr 2022 19:35:00 -0000 [thread overview]
Message-ID: <165039690015.4207.4030717443778774474.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20220414090229.342-1-kuyo.chang@mediatek.com>
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 40f5aa4c5eaebfeaca4566217cb9c468e28ed682
Gitweb: https://git.kernel.org/tip/40f5aa4c5eaebfeaca4566217cb9c468e28ed682
Author: kuyo chang <kuyo.chang@mediatek.com>
AuthorDate: Thu, 14 Apr 2022 17:02:20 +08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 19 Apr 2022 21:15:41 +02:00
sched/pelt: Fix attach_entity_load_avg() corner case
The warning in cfs_rq_is_decayed() triggered:
SCHED_WARN_ON(cfs_rq->avg.load_avg ||
cfs_rq->avg.util_avg ||
cfs_rq->avg.runnable_avg)
There exists a corner case in attach_entity_load_avg() which will
cause load_sum to be zero while load_avg will not be.
Consider se_weight is 88761 as per the sched_prio_to_weight[] table.
Further assume the get_pelt_divider() is 47742, this gives:
se->avg.load_avg is 1.
However, calculating load_sum:
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.
Then enqueue_load_avg() adds this to the cfs_rq totals:
cfs_rq->avg.load_avg += se->avg.load_avg;
cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
Resulting in load_avg being 1 with load_sum is 0, which will trigger
the WARN.
Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq and its se")
Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
[peterz: massage changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lkml.kernel.org/r/20220414090229.342-1-kuyo.chang@mediatek.com
---
kernel/sched/fair.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4bd299..a68482d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3829,11 +3829,11 @@ 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 =
- div_u64(se->avg.load_avg * se->avg.load_sum, 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_sum, se_weight(se));
+ else
+ se->avg.load_sum = 1;
enqueue_load_avg(cfs_rq, se);
cfs_rq->avg.util_avg += se->avg.util_avg;
prev parent reply other threads:[~2022-04-19 19:35 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-14 9:02 [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method Kuyo Chang
2022-04-14 14:44 ` Peter Zijlstra
2022-04-15 3:56 ` Kuyo Chang
2022-04-19 19:35 ` tip-bot2 for kuyo chang [this message]
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