[PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Kuyo Chang]

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 zero and
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.

After all, I refer the following commit patch to do the similar thing at
enqueue_load_avg.
sched/pelt: Relax the sync of load_sum with 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>
---
 kernel/sched/fair.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d4bd299d67ab..30d8b6dba249 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static inline void
 enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	cfs_rq->avg.load_avg += se->avg.load_avg;
-	cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
+	add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
+	add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
+	cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
+					  cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
 }
 
 static inline void
-- 
2.18.0

Re: [PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Peter Zijlstra]

On Mon, Apr 11, 2022 at 02:16:56PM +0800, Kuyo Chang 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 zero and
> 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.
> 
> After all, I refer the following commit patch to do the similar thing at
> enqueue_load_avg.
> sched/pelt: Relax the sync of load_sum with load_avg

  2d02fa8cc21a ("sched/pelt: Relax the sync of load_sum with load_avg")

> 
> After long time testing, the kernel warning was gone and the system runs
> as well as before.
> 

Could probably do with a Fixes: tag too

> Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
> ---
>  kernel/sched/fair.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d4bd299d67ab..30d8b6dba249 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  static inline void
>  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -	cfs_rq->avg.load_avg += se->avg.load_avg;
> -	cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
> +	add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> +	add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
> +	cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> +					  cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
>  }

Yes,. that looks right. Looking at this again though, I wonder if we
should perhaps clean is all up a bit.

Does something like the below on top make sense?


---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3071,23 +3071,37 @@ account_entity_dequeue(struct cfs_rq *cf
 } while (0)
 
 #ifdef CONFIG_SMP
+
+/*
+ * Because of rounding, se->util_sum might ends up being +1 more than
+ * cfs->util_sum. Although this is not a problem by itself, detaching
+ * a lot of tasks with the rounding problem between 2 updates of
+ * util_avg (~1ms) can make cfs->util_sum becoming null whereas
+ * cfs_util_avg is not.
+ *
+ * Check that util_sum is still above its lower bound for the new
+ * util_avg. Given that period_contrib might have moved since the last
+ * sync, we are only sure that util_sum must be above or equal to
+ *    util_avg * minimum possible divider
+ */
+#define __update_sa(sa, name, delta_avg, delta_sum) do {	\
+	add_positive(&(sa)->name##_avg, delta_avg);		\
+	add_positive(&(sa)->name##_sum, delta_sum);		\
+	(sa)->name##_sum = max_t(typeof((sa)->name##_sum),	\
+			       (sa)->name##_sum,		\
+			       (sa)->name##_avg * PELT_MIN_DIVIDER); \
+} while (0)
+
 static inline void
 enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
-	add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
-	cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
-					  cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
+	__update_sa(&cfs_rq->avg, load, se->avg.load_avg, se->avg.load_sum);
 }
 
 static inline void
 dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
-	sub_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
-	sub_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
-	/* See update_cfs_rq_load_avg() */
-	cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
-					  cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
+	__update_sa(&cfs_rq->avg, load, -se->avg.load_avg, -se->avg.load_sum);
 }
 #else
 static inline void
@@ -3529,12 +3543,7 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq
 	se->avg.util_sum = new_sum;
 
 	/* Update parent cfs_rq utilization */
-	add_positive(&cfs_rq->avg.util_avg, delta_avg);
-	add_positive(&cfs_rq->avg.util_sum, delta_sum);
-
-	/* See update_cfs_rq_load_avg() */
-	cfs_rq->avg.util_sum = max_t(u32, cfs_rq->avg.util_sum,
-					  cfs_rq->avg.util_avg * PELT_MIN_DIVIDER);
+	__update_sa(&cfs_rq->avg, util, delta_avg, delta_sum);
 }
 
 static inline void
@@ -3560,11 +3569,7 @@ update_tg_cfs_runnable(struct cfs_rq *cf
 	se->avg.runnable_sum = new_sum;
 
 	/* Update parent cfs_rq runnable */
-	add_positive(&cfs_rq->avg.runnable_avg, delta_avg);
-	add_positive(&cfs_rq->avg.runnable_sum, delta_sum);
-	/* See update_cfs_rq_load_avg() */
-	cfs_rq->avg.runnable_sum = max_t(u32, cfs_rq->avg.runnable_sum,
-					      cfs_rq->avg.runnable_avg * PELT_MIN_DIVIDER);
+	__update_sa(&cfs_rq->avg, runnable, delta_avg, delta_sum);
 }
 
 static inline void
@@ -3628,11 +3633,7 @@ update_tg_cfs_load(struct cfs_rq *cfs_rq
 
 	se->avg.load_sum = runnable_sum;
 	se->avg.load_avg = load_avg;
-	add_positive(&cfs_rq->avg.load_avg, delta_avg);
-	add_positive(&cfs_rq->avg.load_sum, delta_sum);
-	/* See update_cfs_rq_load_avg() */
-	cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
-					  cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
+	__update_sa(&cfs_rq->avg, load, delta_avg, delta_sum);
 }
 
 static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum)
@@ -3747,33 +3748,13 @@ update_cfs_rq_load_avg(u64 now, struct c
 		raw_spin_unlock(&cfs_rq->removed.lock);
 
 		r = removed_load;
-		sub_positive(&sa->load_avg, r);
-		sub_positive(&sa->load_sum, r * divider);
-		/* See sa->util_sum below */
-		sa->load_sum = max_t(u32, sa->load_sum, sa->load_avg * PELT_MIN_DIVIDER);
+		__update_sa(sa, load, r, r*divider);
 
 		r = removed_util;
-		sub_positive(&sa->util_avg, r);
-		sub_positive(&sa->util_sum, r * divider);
-		/*
-		 * Because of rounding, se->util_sum might ends up being +1 more than
-		 * cfs->util_sum. Although this is not a problem by itself, detaching
-		 * a lot of tasks with the rounding problem between 2 updates of
-		 * util_avg (~1ms) can make cfs->util_sum becoming null whereas
-		 * cfs_util_avg is not.
-		 * Check that util_sum is still above its lower bound for the new
-		 * util_avg. Given that period_contrib might have moved since the last
-		 * sync, we are only sure that util_sum must be above or equal to
-		 *    util_avg * minimum possible divider
-		 */
-		sa->util_sum = max_t(u32, sa->util_sum, sa->util_avg * PELT_MIN_DIVIDER);
+		__update_sa(sa, util, r, r*divider);
 
 		r = removed_runnable;
-		sub_positive(&sa->runnable_avg, r);
-		sub_positive(&sa->runnable_sum, r * divider);
-		/* See sa->util_sum above */
-		sa->runnable_sum = max_t(u32, sa->runnable_sum,
-					      sa->runnable_avg * PELT_MIN_DIVIDER);
+		__update_sa(sa, runnable, r, r*divider);
 
 		/*
 		 * removed_runnable is the unweighted version of removed_load so we
@@ -3861,17 +3842,8 @@ static void attach_entity_load_avg(struc
 static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
 	dequeue_load_avg(cfs_rq, se);
-	sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
-	sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);
-	/* See update_cfs_rq_load_avg() */
-	cfs_rq->avg.util_sum = max_t(u32, cfs_rq->avg.util_sum,
-					  cfs_rq->avg.util_avg * PELT_MIN_DIVIDER);
-
-	sub_positive(&cfs_rq->avg.runnable_avg, se->avg.runnable_avg);
-	sub_positive(&cfs_rq->avg.runnable_sum, se->avg.runnable_sum);
-	/* See update_cfs_rq_load_avg() */
-	cfs_rq->avg.runnable_sum = max_t(u32, cfs_rq->avg.runnable_sum,
-					      cfs_rq->avg.runnable_avg * PELT_MIN_DIVIDER);
+	__update_sa(&cfs_rq->avg, util, se->avg.util_avg, se->avg.util_sum);
+	__update_sa(&cfs_rq->avg, runnable, se->avg.runnable_avg, se->avg.runnable_sum);
 
 	add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
 

Re: [PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Vincent Guittot]

On Mon, 11 Apr 2022 at 08:17, 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 zero and
> 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.

The root problem is there, se->avg.load_sum must not be null if
se->avg.load_avg is not null because the correct relation between _avg
and _sum is:

load_avg = weight * load_sum / divider.

so the fix should be attach_entity_load_avg() and probably the below is enough

se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum,
se_weight(se)) + 1;

>
> 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.
>
> After all, I refer the following commit patch to do the similar thing at
> enqueue_load_avg.
> sched/pelt: Relax the sync of load_sum with 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>
> ---
>  kernel/sched/fair.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d4bd299d67ab..30d8b6dba249 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  static inline void
>  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -       cfs_rq->avg.load_avg += se->avg.load_avg;
> -       cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
> +       add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> +       add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
> +       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> +                                         cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
>  }
>
>  static inline void
> --
> 2.18.0
>

Re: [PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Vincent Guittot]

On Mon, 11 Apr 2022 at 10:25, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 11, 2022 at 02:16:56PM +0800, Kuyo Chang 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 zero and
> > 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.
> >
> > After all, I refer the following commit patch to do the similar thing at
> > enqueue_load_avg.
> > sched/pelt: Relax the sync of load_sum with load_avg
>
>   2d02fa8cc21a ("sched/pelt: Relax the sync of load_sum with load_avg")
>
> >
> > After long time testing, the kernel warning was gone and the system runs
> > as well as before.
> >
>
> Could probably do with a Fixes: tag too
>
> > Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
> > ---
> >  kernel/sched/fair.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d4bd299d67ab..30d8b6dba249 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  static inline void
> >  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  {
> > -     cfs_rq->avg.load_avg += se->avg.load_avg;
> > -     cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
> > +     add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> > +     add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
> > +     cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> > +                                       cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
> >  }
>
> Yes,. that looks right. Looking at this again though, I wonder if we
> should perhaps clean is all up a bit.

adding se->load_avg|sum in cfs_rq should not create a situation where
cfs->load_sum is null but not cfs->load_avg unless se->load_avg|sum
are wrong from the beginning which seems to be the case here

>
> Does something like the below on top make sense?
>
>
> ---
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3071,23 +3071,37 @@ account_entity_dequeue(struct cfs_rq *cf
>  } while (0)
>
>  #ifdef CONFIG_SMP
> +
> +/*
> + * Because of rounding, se->util_sum might ends up being +1 more than
> + * cfs->util_sum. Although this is not a problem by itself, detaching
> + * a lot of tasks with the rounding problem between 2 updates of
> + * util_avg (~1ms) can make cfs->util_sum becoming null whereas
> + * cfs_util_avg is not.
> + *
> + * Check that util_sum is still above its lower bound for the new
> + * util_avg. Given that period_contrib might have moved since the last
> + * sync, we are only sure that util_sum must be above or equal to
> + *    util_avg * minimum possible divider
> + */
> +#define __update_sa(sa, name, delta_avg, delta_sum) do {       \
> +       add_positive(&(sa)->name##_avg, delta_avg);             \
> +       add_positive(&(sa)->name##_sum, delta_sum);             \
> +       (sa)->name##_sum = max_t(typeof((sa)->name##_sum),      \
> +                              (sa)->name##_sum,                \
> +                              (sa)->name##_avg * PELT_MIN_DIVIDER); \
> +} while (0)
> +
>  static inline void
>  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -       add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> -       add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
> -       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> -                                         cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
> +       __update_sa(&cfs_rq->avg, load, se->avg.load_avg, se->avg.load_sum);
>  }
>
>  static inline void
>  dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
> -       sub_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> -       sub_positive(&cfs_rq->avg.load_sum, se_weight(se) * se->avg.load_sum);
> -       /* See update_cfs_rq_load_avg() */
> -       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> -                                         cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
> +       __update_sa(&cfs_rq->avg, load, -se->avg.load_avg, -se->avg.load_sum);
>  }
>  #else
>  static inline void
> @@ -3529,12 +3543,7 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq
>         se->avg.util_sum = new_sum;
>
>         /* Update parent cfs_rq utilization */
> -       add_positive(&cfs_rq->avg.util_avg, delta_avg);
> -       add_positive(&cfs_rq->avg.util_sum, delta_sum);
> -
> -       /* See update_cfs_rq_load_avg() */
> -       cfs_rq->avg.util_sum = max_t(u32, cfs_rq->avg.util_sum,
> -                                         cfs_rq->avg.util_avg * PELT_MIN_DIVIDER);
> +       __update_sa(&cfs_rq->avg, util, delta_avg, delta_sum);
>  }
>
>  static inline void
> @@ -3560,11 +3569,7 @@ update_tg_cfs_runnable(struct cfs_rq *cf
>         se->avg.runnable_sum = new_sum;
>
>         /* Update parent cfs_rq runnable */
> -       add_positive(&cfs_rq->avg.runnable_avg, delta_avg);
> -       add_positive(&cfs_rq->avg.runnable_sum, delta_sum);
> -       /* See update_cfs_rq_load_avg() */
> -       cfs_rq->avg.runnable_sum = max_t(u32, cfs_rq->avg.runnable_sum,
> -                                             cfs_rq->avg.runnable_avg * PELT_MIN_DIVIDER);
> +       __update_sa(&cfs_rq->avg, runnable, delta_avg, delta_sum);
>  }
>
>  static inline void
> @@ -3628,11 +3633,7 @@ update_tg_cfs_load(struct cfs_rq *cfs_rq
>
>         se->avg.load_sum = runnable_sum;
>         se->avg.load_avg = load_avg;
> -       add_positive(&cfs_rq->avg.load_avg, delta_avg);
> -       add_positive(&cfs_rq->avg.load_sum, delta_sum);
> -       /* See update_cfs_rq_load_avg() */
> -       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> -                                         cfs_rq->avg.load_avg * PELT_MIN_DIVIDER);
> +       __update_sa(&cfs_rq->avg, load, delta_avg, delta_sum);
>  }
>
>  static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum)
> @@ -3747,33 +3748,13 @@ update_cfs_rq_load_avg(u64 now, struct c
>                 raw_spin_unlock(&cfs_rq->removed.lock);
>
>                 r = removed_load;
> -               sub_positive(&sa->load_avg, r);
> -               sub_positive(&sa->load_sum, r * divider);
> -               /* See sa->util_sum below */
> -               sa->load_sum = max_t(u32, sa->load_sum, sa->load_avg * PELT_MIN_DIVIDER);
> +               __update_sa(sa, load, r, r*divider);
>
>                 r = removed_util;
> -               sub_positive(&sa->util_avg, r);
> -               sub_positive(&sa->util_sum, r * divider);
> -               /*
> -                * Because of rounding, se->util_sum might ends up being +1 more than
> -                * cfs->util_sum. Although this is not a problem by itself, detaching
> -                * a lot of tasks with the rounding problem between 2 updates of
> -                * util_avg (~1ms) can make cfs->util_sum becoming null whereas
> -                * cfs_util_avg is not.
> -                * Check that util_sum is still above its lower bound for the new
> -                * util_avg. Given that period_contrib might have moved since the last
> -                * sync, we are only sure that util_sum must be above or equal to
> -                *    util_avg * minimum possible divider
> -                */
> -               sa->util_sum = max_t(u32, sa->util_sum, sa->util_avg * PELT_MIN_DIVIDER);
> +               __update_sa(sa, util, r, r*divider);
>
>                 r = removed_runnable;
> -               sub_positive(&sa->runnable_avg, r);
> -               sub_positive(&sa->runnable_sum, r * divider);
> -               /* See sa->util_sum above */
> -               sa->runnable_sum = max_t(u32, sa->runnable_sum,
> -                                             sa->runnable_avg * PELT_MIN_DIVIDER);
> +               __update_sa(sa, runnable, r, r*divider);
>
>                 /*
>                  * removed_runnable is the unweighted version of removed_load so we
> @@ -3861,17 +3842,8 @@ static void attach_entity_load_avg(struc
>  static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  {
>         dequeue_load_avg(cfs_rq, se);
> -       sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
> -       sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);
> -       /* See update_cfs_rq_load_avg() */
> -       cfs_rq->avg.util_sum = max_t(u32, cfs_rq->avg.util_sum,
> -                                         cfs_rq->avg.util_avg * PELT_MIN_DIVIDER);
> -
> -       sub_positive(&cfs_rq->avg.runnable_avg, se->avg.runnable_avg);
> -       sub_positive(&cfs_rq->avg.runnable_sum, se->avg.runnable_sum);
> -       /* See update_cfs_rq_load_avg() */
> -       cfs_rq->avg.runnable_sum = max_t(u32, cfs_rq->avg.runnable_sum,
> -                                             cfs_rq->avg.runnable_avg * PELT_MIN_DIVIDER);
> +       __update_sa(&cfs_rq->avg, util, se->avg.util_avg, se->avg.util_sum);
> +       __update_sa(&cfs_rq->avg, runnable, se->avg.runnable_avg, se->avg.runnable_sum);
>
>         add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);
>

Re: [PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Kuyo Chang]

On Mon, 2022-04-11 at 10:39 +0200, Vincent Guittot wrote:
> On Mon, 11 Apr 2022 at 08:17, 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 zero
> > and
> > 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.
> 
> The root problem is there, se->avg.load_sum must not be null if
> se->avg.load_avg is not null because the correct relation between
> _avg
> and _sum is:
> 
> load_avg = weight * load_sum / divider.
> 
> so the fix should be attach_entity_load_avg() and probably the below
> is enough
> 
> se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum,
> se_weight(se)) + 1;

Thanks for your kindly suggestion.
+1 would make the calcuation for load_sum may be overestimate?
How about the below code make sense for fix the corner case?

--- 
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3832,7 +3832,8 @@ static void attach_entity_load_avg(struct cfs_rq
*cfs_rq, struct sched_entity *s
 	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_avg * se->avg.load_sum >
se_weight(se)) ?
+			div_u64(se->avg.load_avg * se->avg.load_sum,
se_weight(se)) : 1;
 	}
 
 	enqueue_load_avg(cfs_rq, se);
-- 
2.18.0


> > 
> > 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.
> > 
> > After all, I refer the following commit patch to do the similar
> > thing at
> > enqueue_load_avg.
> > sched/pelt: Relax the sync of load_sum with 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>
> > ---
> >  kernel/sched/fair.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d4bd299d67ab..30d8b6dba249 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq
> > *cfs_rq, struct sched_entity *se)
> >  static inline void
> >  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >  {
> > -       cfs_rq->avg.load_avg += se->avg.load_avg;
> > -       cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
> > +       add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> > +       add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se-
> > >avg.load_sum);
> > +       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> > +                                         cfs_rq->avg.load_avg *
> > PELT_MIN_DIVIDER);
> >  }
> > 
> >  static inline void
> > --
> > 2.18.0
> > 

Re: [PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Vincent Guittot]

Le mardi 12 avril 2022 à 10:51:23 (+0800), Kuyo Chang a écrit :
> On Mon, 2022-04-11 at 10:39 +0200, Vincent Guittot wrote:
> > On Mon, 11 Apr 2022 at 08:17, 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 zero
> > > and
> > > 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.
> > 
> > The root problem is there, se->avg.load_sum must not be null if
> > se->avg.load_avg is not null because the correct relation between
> > _avg
> > and _sum is:
> > 
> > load_avg = weight * load_sum / divider.
> > 
> > so the fix should be attach_entity_load_avg() and probably the below
> > is enough
> > 
> > se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum,
> > se_weight(se)) + 1;
> 
> Thanks for your kindly suggestion.
> +1 would make the calcuation for load_sum may be overestimate?
> How about the below code make sense for fix the corner case?
> 
> --- 
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3832,7 +3832,8 @@ static void attach_entity_load_avg(struct cfs_rq
> *cfs_rq, struct sched_entity *s
>  	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_avg * se->avg.load_sum >
> se_weight(se)) ?
> +			div_u64(se->avg.load_avg * se->avg.load_sum,
> se_weight(se)) : 1;
>  	}
>  
>  	enqueue_load_avg(cfs_rq, se);
> -- 
> 2.18.0

In this case, the below is easier to read

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1658a9428d96..2c685474db23 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3836,10 +3836,12 @@ 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);



> 
> 
> > > 
> > > 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.
> > > 
> > > After all, I refer the following commit patch to do the similar
> > > thing at
> > > enqueue_load_avg.
> > > sched/pelt: Relax the sync of load_sum with 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>
> > > ---
> > >  kernel/sched/fair.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index d4bd299d67ab..30d8b6dba249 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq
> > > *cfs_rq, struct sched_entity *se)
> > >  static inline void
> > >  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > >  {
> > > -       cfs_rq->avg.load_avg += se->avg.load_avg;
> > > -       cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum;
> > > +       add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> > > +       add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se-
> > > >avg.load_sum);
> > > +       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> > > +                                         cfs_rq->avg.load_avg *
> > > PELT_MIN_DIVIDER);
> > >  }
> > > 
> > >  static inline void
> > > --
> > > 2.18.0
> > > 
> 

Re: [PATCH 1/1] sched/pelt: Refine the enqueue_load_avg calculate method

[Kuyo Chang]

On Tue, 2022-04-12 at 10:58 +0200, Vincent Guittot wrote:
> Le mardi 12 avril 2022 à 10:51:23 (+0800), Kuyo Chang a écrit :
> > On Mon, 2022-04-11 at 10:39 +0200, Vincent Guittot wrote:
> > > On Mon, 11 Apr 2022 at 08:17, 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
> > > > zero
> > > > and
> > > > 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.
> > > 
> > > The root problem is there, se->avg.load_sum must not be null if
> > > se->avg.load_avg is not null because the correct relation between
> > > _avg
> > > and _sum is:
> > > 
> > > load_avg = weight * load_sum / divider.
> > > 
> > > so the fix should be attach_entity_load_avg() and probably the
> > > below
> > > is enough
> > > 
> > > se->avg.load_sum = div_u64(se->avg.load_avg * se->avg.load_sum,
> > > se_weight(se)) + 1;
> > 
> > Thanks for your kindly suggestion.
> > +1 would make the calcuation for load_sum may be overestimate?
> > How about the below code make sense for fix the corner case?
> > 
> > --- 
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3832,7 +3832,8 @@ static void attach_entity_load_avg(struct
> > cfs_rq
> > *cfs_rq, struct sched_entity *s
> >  	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_avg * se->avg.load_sum >
> > se_weight(se)) ?
> > +			div_u64(se->avg.load_avg * se->avg.load_sum,
> > se_weight(se)) : 1;
> >  	}
> >  
> >  	enqueue_load_avg(cfs_rq, se);
> > -- 
> > 2.18.0
> 
> In this case, the below is easier to read
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1658a9428d96..2c685474db23 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3836,10 +3836,12 @@ 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);

It really easier to read.
Thanks for your kindly suggestion.


> 
> 
> > 
> > 
> > > > 
> > > > 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.
> > > > 
> > > > After all, I refer the following commit patch to do the similar
> > > > thing at
> > > > enqueue_load_avg.
> > > > sched/pelt: Relax the sync of load_sum with 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>
> > > > ---
> > > >  kernel/sched/fair.c | 6 ++++--
> > > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > > index d4bd299d67ab..30d8b6dba249 100644
> > > > --- a/kernel/sched/fair.c
> > > > +++ b/kernel/sched/fair.c
> > > > @@ -3074,8 +3074,10 @@ account_entity_dequeue(struct cfs_rq
> > > > *cfs_rq, struct sched_entity *se)
> > > >  static inline void
> > > >  enqueue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity
> > > > *se)
> > > >  {
> > > > -       cfs_rq->avg.load_avg += se->avg.load_avg;
> > > > -       cfs_rq->avg.load_sum += se_weight(se) * se-
> > > > >avg.load_sum;
> > > > +       add_positive(&cfs_rq->avg.load_avg, se->avg.load_avg);
> > > > +       add_positive(&cfs_rq->avg.load_sum, se_weight(se) * se-
> > > > > avg.load_sum);
> > > > 
> > > > +       cfs_rq->avg.load_sum = max_t(u32, cfs_rq->avg.load_sum,
> > > > +                                         cfs_rq->avg.load_avg
> > > > *
> > > > PELT_MIN_DIVIDER);
> > > >  }
> > > > 
> > > >  static inline void
> > > > --
> > > > 2.18.0
> > > >