* [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method
@ 2022-04-14 1:59 Kuyo Chang
2022-04-14 7:37 ` Vincent Guittot
2022-04-14 9:02 ` Dietmar Eggemann
0 siblings, 2 replies; 5+ messages in thread
From: Kuyo Chang @ 2022-04-14 1:59 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, 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.
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.
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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^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method
2022-04-14 1:59 [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method Kuyo Chang
@ 2022-04-14 7:37 ` Vincent Guittot
2022-04-14 8:25 ` Kuyo Chang
2022-04-14 9:02 ` Dietmar Eggemann
1 sibling, 1 reply; 5+ messages in thread
From: Vincent Guittot @ 2022-04-14 7:37 UTC (permalink / raw)
To: Kuyo Chang
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger, wsd_upstream,
linux-kernel, linux-arm-kernel, linux-mediatek
On Thu, 14 Apr 2022 at 03:59, Kuyo Chang <kuyo.chang@mediatek.com> wrote:
>
> 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.
This needs a fix tag:
Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq and its se")
>
> Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
>
> 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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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method
2022-04-14 7:37 ` Vincent Guittot
@ 2022-04-14 8:25 ` Kuyo Chang
0 siblings, 0 replies; 5+ messages in thread
From: Kuyo Chang @ 2022-04-14 8:25 UTC (permalink / raw)
To: Vincent Guittot
Cc: Ingo Molnar, Peter Zijlstra, Juri Lelli, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger, wsd_upstream,
linux-kernel, linux-arm-kernel, linux-mediatek
On Thu, 2022-04-14 at 09:37 +0200, Vincent Guittot wrote:
> On Thu, 14 Apr 2022 at 03:59, Kuyo Chang <kuyo.chang@mediatek.com>
> wrote:
> >
> > 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.
>
> This needs a fix tag:
> Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq
> and its se")
Thanks for your friendly reminder.
> >
> > Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
>
> > ---
> >
> > 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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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method
2022-04-14 1:59 [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method Kuyo Chang
2022-04-14 7:37 ` Vincent Guittot
@ 2022-04-14 9:02 ` Dietmar Eggemann
2022-04-14 9:29 ` Kuyo Chang
1 sibling, 1 reply; 5+ messages in thread
From: Dietmar Eggemann @ 2022-04-14 9:02 UTC (permalink / raw)
To: Kuyo Chang, Ingo Molnar, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger
Cc: wsd_upstream, linux-kernel, linux-arm-kernel, linux-mediatek
On 14/04/2022 03:59, Kuyo Chang wrote:
> From: kuyo chang <kuyo.chang@mediatek.com>
[...]
> 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));
Seems that this will fit on one line now. No braces needed then.
> + } else {
> + se->avg.load_sum = 1;
> }
>
> enqueue_load_avg(cfs_rq, se);
Looks like taskgroups are not affected since they get always online
with cpu.shares/weight = 1024 (cgroup v1):
cpu_cgroup_css_online() -> online_fair_sched_group() ->
attach_entity_cfs_rq() -> attach_entity_load_avg()
And reweight_entity() does not have this issue.
Tested with `qemu-system-x86_64 ... cores=64 ... -enable-kvm` and
weight=88761 for nice=0 tasks plus forcing se->avg.load_avg = 1 before
the div_u64() in attach_entity_load_avg().
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method
2022-04-14 9:02 ` Dietmar Eggemann
@ 2022-04-14 9:29 ` Kuyo Chang
0 siblings, 0 replies; 5+ messages in thread
From: Kuyo Chang @ 2022-04-14 9:29 UTC (permalink / raw)
To: Dietmar Eggemann, Ingo Molnar, Peter Zijlstra, Juri Lelli,
Vincent Guittot, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Matthias Brugger
Cc: wsd_upstream, linux-kernel, linux-arm-kernel, linux-mediatek
On Thu, 2022-04-14 at 11:02 +0200, Dietmar Eggemann wrote:
> On 14/04/2022 03:59, Kuyo Chang wrote:
> > From: kuyo chang <kuyo.chang@mediatek.com>
>
> [...]
>
> > 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));
>
> Seems that this will fit on one line now. No braces needed then.
Thanks for your friendly reminder.
>
> > + } else {
> > + se->avg.load_sum = 1;
> > }
> >
> > enqueue_load_avg(cfs_rq, se);
>
> Looks like taskgroups are not affected since they get always online
> with cpu.shares/weight = 1024 (cgroup v1):
>
> cpu_cgroup_css_online() -> online_fair_sched_group() ->
> attach_entity_cfs_rq() -> attach_entity_load_avg()
>
> And reweight_entity() does not have this issue.
>
> Tested with `qemu-system-x86_64 ... cores=64 ... -enable-kvm` and
> weight=88761 for nice=0 tasks plus forcing se->avg.load_avg = 1
> before
> the div_u64() in attach_entity_load_avg().
>
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
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^ permalink raw reply [flat|nested] 5+ messages in thread
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2022-04-14 1:59 [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method Kuyo Chang
2022-04-14 7:37 ` Vincent Guittot
2022-04-14 8:25 ` Kuyo Chang
2022-04-14 9:02 ` Dietmar Eggemann
2022-04-14 9:29 ` Kuyo Chang
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