* [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method
@ 2022-04-14 9:02 Kuyo Chang
2022-04-14 14:44 ` Peter Zijlstra
2022-04-19 19:35 ` [tip: sched/urgent] sched/pelt: Fix attach_entity_load_avg() corner case tip-bot2 for kuyo chang
0 siblings, 2 replies; 4+ messages in thread
From: Kuyo Chang @ 2022-04-14 9:02 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot,
Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger
Cc: wsd_upstream, kuyo chang, Ingo Molnar, linux-kernel,
linux-arm-kernel, linux-mediatek
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
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method
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: sched/urgent] sched/pelt: Fix attach_entity_load_avg() corner case tip-bot2 for kuyo chang
1 sibling, 1 reply; 4+ messages in thread
From: Peter Zijlstra @ 2022-04-14 14:44 UTC (permalink / raw)
To: Kuyo Chang
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger, wsd_upstream,
Ingo Molnar, linux-kernel, linux-arm-kernel, linux-mediatek
I've taken the liberty of carrying over the tags from v2 and reworked
the Changelog a little.
---
Subject: sched/pelt: Fix attach_entity_load_avg() corner case
From: kuyo chang <kuyo.chang@mediatek.com>
Date: Thu, 14 Apr 2022 17:02:20 +0800
From: kuyo chang <kuyo.chang@mediatek.com>
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 results in 0:
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(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3829,11 +3829,11 @@ static void attach_entity_load_avg(struc
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;
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH 1/1] [PATCH v3]sched/pelt: Fix the attach_entity_load_avg calculate method
2022-04-14 14:44 ` Peter Zijlstra
@ 2022-04-15 3:56 ` Kuyo Chang
0 siblings, 0 replies; 4+ messages in thread
From: Kuyo Chang @ 2022-04-15 3:56 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger, wsd_upstream,
Ingo Molnar, linux-kernel, linux-arm-kernel, linux-mediatek
On Thu, 2022-04-14 at 16:44 +0200, Peter Zijlstra wrote:
> I've taken the liberty of carrying over the tags from v2 and reworked
> the Changelog a little.
Thank you for all your assistance.
> ---
> Subject: sched/pelt: Fix attach_entity_load_avg() corner case
> From: kuyo chang <kuyo.chang@mediatek.com>
> Date: Thu, 14 Apr 2022 17:02:20 +0800
>
> From: kuyo chang <kuyo.chang@mediatek.com>
>
> 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 results in 0:
>
> 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://urldefense.com/v3/__https://lkml.kernel.org/r/20220414090229.342-1-kuyo.chang@mediatek.com__;!!CTRNKA9wMg0ARbw!35Im02xxIuUZdLYpPng37Yk7oVNJVJ1tfbu4XRzlq-6VhH3K29Por0gJCFlslT_CMgA$
>
> ---
> kernel/sched/fair.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3829,11 +3829,11 @@ static void attach_entity_load_avg(struc
>
> 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;
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip: sched/urgent] sched/pelt: Fix attach_entity_load_avg() corner case
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
@ 2022-04-19 19:35 ` tip-bot2 for kuyo chang
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot2 for kuyo chang @ 2022-04-19 19:35 UTC (permalink / raw)
To: linux-tip-commits
Cc: kuyo chang, Peter Zijlstra (Intel),
Vincent Guittot, Dietmar Eggemann, x86, linux-kernel
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;
^ permalink raw reply related [flat|nested] 4+ messages in thread
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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: sched/urgent] sched/pelt: Fix attach_entity_load_avg() corner case tip-bot2 for kuyo chang
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