[PATCH] sched/uclamp: Fix uclamp_tg_restrict()

[PATCH] sched/uclamp: Fix uclamp_tg_restrict()

[Qais Yousef]

Now cpu.uclamp.min acts as a protection, we need to make sure that the
uclamp request of the task is within the allowed range of the cgroup,
that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
tg->uclamp[UCLAMP_MAX].

As reported by Xuewen [1] we can have some corner cases where there's
inverstion between uclamp requested by task (p) and the uclamp values of
the taskgroup it's attached to (tg). Following table demonstrates
2 corner cases:

	           |  p  |  tg  |  effective
	-----------+-----+------+-----------
	CASE 1
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   |  60%
	-----------+-----+------+-----------
	uclamp_max | 80% | 50%  |  50%
	-----------+-----+------+-----------
	CASE 2
	-----------+-----+------+-----------
	uclamp_min | 0%  | 30%  |  30%
	-----------+-----+------+-----------
	uclamp_max | 20% | 50%  |  20%
	-----------+-----+------+-----------

With this fix we get:

	           |  p  |  tg  |  effective
	-----------+-----+------+-----------
	CASE 1
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   |  50%
	-----------+-----+------+-----------
	uclamp_max | 80% | 50%  |  50%
	-----------+-----+------+-----------
	CASE 2
	-----------+-----+------+-----------
	uclamp_min | 0%  | 30%  |  30%
	-----------+-----+------+-----------
	uclamp_max | 20% | 50%  |  30%
	-----------+-----+------+-----------

Additionally uclamp_update_active_tasks() must now unconditionally
update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for
instance could have an impact on the effective UCLAMP_MIN of the tasks.

	           |  p  |  tg  |  effective
	-----------+-----+------+-----------
	old
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   |  50%
	-----------+-----+------+-----------
	uclamp_max | 80% | 50%  |  50%
	-----------+-----+------+-----------
	*new*
	-----------+-----+------+-----------
	uclamp_min | 60% | 0%   | *60%*
	-----------+-----+------+-----------
	uclamp_max | 80% |*70%* | *70%*
	-----------+-----+------+-----------

[1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/

Reported-by: Xuewen Yan <xuewen.yan94@gmail.com>
Fixes: 0c18f2ecfcc2 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min")
Signed-off-by: Qais Yousef <qais.yousef@arm.com>
---

Xuewen, Yun, Wei

If you can give this a spin and provide Tested-by that would be much
appreciated.

Thanks!


 kernel/sched/core.c | 43 +++++++++++++++----------------------------
 1 file changed, 15 insertions(+), 28 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9e9a5be35cde..0318b00baa97 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
 static inline struct uclamp_se
 uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
 {
-	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
+	/* Copy by value as we could modify it */
+	struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
 #ifdef CONFIG_UCLAMP_TASK_GROUP
+	unsigned int tg_min, tg_max, value;
 
 	/*
 	 * Tasks in autogroups or root task group will be
 	 * restricted by system defaults.
 	 */
 	if (task_group_is_autogroup(task_group(p)))
-		return uc_req;
+		return uc_eff;
 	if (task_group(p) == &root_task_group)
-		return uc_req;
+		return uc_eff;
 
-	switch (clamp_id) {
-	case UCLAMP_MIN: {
-		struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
-		if (uc_req.value < uc_min.value)
-			return uc_min;
-		break;
-	}
-	case UCLAMP_MAX: {
-		struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
-		if (uc_req.value > uc_max.value)
-			return uc_max;
-		break;
-	}
-	default:
-		WARN_ON_ONCE(1);
-		break;
-	}
+	tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
+	tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
+	value = uc_eff.value;
+	value = clamp(value, tg_min, tg_max);
+	uclamp_se_set(&uc_eff, value, false);
 #endif
 
-	return uc_req;
+	return uc_eff;
 }
 
 /*
@@ -1661,8 +1651,7 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
 
 #ifdef CONFIG_UCLAMP_TASK_GROUP
 static inline void
-uclamp_update_active_tasks(struct cgroup_subsys_state *css,
-			   unsigned int clamps)
+uclamp_update_active_tasks(struct cgroup_subsys_state *css)
 {
 	enum uclamp_id clamp_id;
 	struct css_task_iter it;
@@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
 
 	css_task_iter_start(css, 0, &it);
 	while ((p = css_task_iter_next(&it))) {
-		for_each_clamp_id(clamp_id) {
-			if ((0x1 << clamp_id) & clamps)
-				uclamp_update_active(p, clamp_id);
-		}
+		for_each_clamp_id(clamp_id)
+			uclamp_update_active(p, clamp_id);
 	}
 	css_task_iter_end(&it);
 }
@@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
 		}
 
 		/* Immediately update descendants RUNNABLE tasks */
-		uclamp_update_active_tasks(css, clamps);
+		uclamp_update_active_tasks(css);
 	}
 }
 
-- 
2.25.1

Re: [PATCH] sched/uclamp: Fix uclamp_tg_restrict()

[Xuewen Yan]

Hi Qais

Sorry for the late reply.

I tested the patch on the "UNISOC T610" platform, and it looks fine.

According to the two cases:
case1:
without patch:
set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
[  215.780435]c6  uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=614,eff_max=819

after set tg's cpu.uclamp.max = 50%，the result:
[  420.580443]c6  uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=614,eff_max=512

with patch:
set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
[  333.533878]c7  uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=614,eff_max=819

after set tg's cpu.uclamp.max = 50%，the result:
[  430.813789]c6  uclamp_test :
pid=138,req_min=614,req_max=819,eff_min=512,eff_max=512

case2:
without patch:
set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
[  169.700544]c0  uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=0,eff_max=209

after set tg's cpu.uclamp.min = 30%, tg's cpu.uclamp.max = 50%，the result:
[  246.500634]c7  uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=307,eff_max=209

with patch:
set task's clamp_min=0(0%), clamp_max=209(20%), the result as:
[  169.700544]c0  uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=0,eff_max=209

after set tg's cpu.uclamp.min = 30%, tg's cpu.uclamp.max = 50%，the result:
[  179.933868]c6  uclamp_test :
pid=137,req_min=0,req_max=209,eff_min=307,eff_max=307

---
Cheers

xuewen

On Fri, Jun 11, 2021 at 8:23 PM Qais Yousef <qais.yousef@arm.com> wrote:
>
> Now cpu.uclamp.min acts as a protection, we need to make sure that the
> uclamp request of the task is within the allowed range of the cgroup,
> that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
> tg->uclamp[UCLAMP_MAX].
>
> As reported by Xuewen [1] we can have some corner cases where there's
> inverstion between uclamp requested by task (p) and the uclamp values of
> the taskgroup it's attached to (tg). Following table demonstrates
> 2 corner cases:
>
>                    |  p  |  tg  |  effective
>         -----------+-----+------+-----------
>         CASE 1
>         -----------+-----+------+-----------
>         uclamp_min | 60% | 0%   |  60%
>         -----------+-----+------+-----------
>         uclamp_max | 80% | 50%  |  50%
>         -----------+-----+------+-----------
>         CASE 2
>         -----------+-----+------+-----------
>         uclamp_min | 0%  | 30%  |  30%
>         -----------+-----+------+-----------
>         uclamp_max | 20% | 50%  |  20%
>         -----------+-----+------+-----------
>
> With this fix we get:
>
>                    |  p  |  tg  |  effective
>         -----------+-----+------+-----------
>         CASE 1
>         -----------+-----+------+-----------
>         uclamp_min | 60% | 0%   |  50%
>         -----------+-----+------+-----------
>         uclamp_max | 80% | 50%  |  50%
>         -----------+-----+------+-----------
>         CASE 2
>         -----------+-----+------+-----------
>         uclamp_min | 0%  | 30%  |  30%
>         -----------+-----+------+-----------
>         uclamp_max | 20% | 50%  |  30%
>         -----------+-----+------+-----------
>
> Additionally uclamp_update_active_tasks() must now unconditionally
> update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for
> instance could have an impact on the effective UCLAMP_MIN of the tasks.
>
>                    |  p  |  tg  |  effective
>         -----------+-----+------+-----------
>         old
>         -----------+-----+------+-----------
>         uclamp_min | 60% | 0%   |  50%
>         -----------+-----+------+-----------
>         uclamp_max | 80% | 50%  |  50%
>         -----------+-----+------+-----------
>         *new*
>         -----------+-----+------+-----------
>         uclamp_min | 60% | 0%   | *60%*
>         -----------+-----+------+-----------
>         uclamp_max | 80% |*70%* | *70%*
>         -----------+-----+------+-----------
>
> [1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/
>
> Reported-by: Xuewen Yan <xuewen.yan94@gmail.com>
> Fixes: 0c18f2ecfcc2 ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min")
> Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> ---
>
> Xuewen, Yun, Wei
>
> If you can give this a spin and provide Tested-by that would be much
> appreciated.
>
> Thanks!
>
>
>  kernel/sched/core.c | 43 +++++++++++++++----------------------------
>  1 file changed, 15 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9e9a5be35cde..0318b00baa97 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
>  static inline struct uclamp_se
>  uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
>  {
> -       struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> +       /* Copy by value as we could modify it */
> +       struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
>  #ifdef CONFIG_UCLAMP_TASK_GROUP
> +       unsigned int tg_min, tg_max, value;
>
>         /*
>          * Tasks in autogroups or root task group will be
>          * restricted by system defaults.
>          */
>         if (task_group_is_autogroup(task_group(p)))
> -               return uc_req;
> +               return uc_eff;
>         if (task_group(p) == &root_task_group)
> -               return uc_req;
> +               return uc_eff;
>
> -       switch (clamp_id) {
> -       case UCLAMP_MIN: {
> -               struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
> -               if (uc_req.value < uc_min.value)
> -                       return uc_min;
> -               break;
> -       }
> -       case UCLAMP_MAX: {
> -               struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
> -               if (uc_req.value > uc_max.value)
> -                       return uc_max;
> -               break;
> -       }
> -       default:
> -               WARN_ON_ONCE(1);
> -               break;
> -       }
> +       tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
> +       tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
> +       value = uc_eff.value;
> +       value = clamp(value, tg_min, tg_max);
> +       uclamp_se_set(&uc_eff, value, false);
>  #endif
>
> -       return uc_req;
> +       return uc_eff;
>  }
>
>  /*
> @@ -1661,8 +1651,7 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
>
>  #ifdef CONFIG_UCLAMP_TASK_GROUP
>  static inline void
> -uclamp_update_active_tasks(struct cgroup_subsys_state *css,
> -                          unsigned int clamps)
> +uclamp_update_active_tasks(struct cgroup_subsys_state *css)
>  {
>         enum uclamp_id clamp_id;
>         struct css_task_iter it;
> @@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
>
>         css_task_iter_start(css, 0, &it);
>         while ((p = css_task_iter_next(&it))) {
> -               for_each_clamp_id(clamp_id) {
> -                       if ((0x1 << clamp_id) & clamps)
> -                               uclamp_update_active(p, clamp_id);
> -               }
> +               for_each_clamp_id(clamp_id)
> +                       uclamp_update_active(p, clamp_id);
>         }
>         css_task_iter_end(&it);
>  }
> @@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
>                 }
>
>                 /* Immediately update descendants RUNNABLE tasks */
> -               uclamp_update_active_tasks(css, clamps);
> +               uclamp_update_active_tasks(css);
>         }
>  }
>
> --
> 2.25.1
>

Re: [PATCH] sched/uclamp: Fix uclamp_tg_restrict()

[Qais Yousef]

Hi Xuewen

On 06/16/21 11:06, Xuewen Yan wrote:
> Hi Qais
> 
> Sorry for the late reply.
> 
> I tested the patch on the "UNISOC T610" platform, and it looks fine.
> 
> According to the two cases:
> case1:
> without patch:
> set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
> [  215.780435]c6  uclamp_test :
> pid=138,req_min=614,req_max=819,eff_min=614,eff_max=819
> 
> after set tg's cpu.uclamp.max = 50%，the result:
> [  420.580443]c6  uclamp_test :
> pid=138,req_min=614,req_max=819,eff_min=614,eff_max=512
> 
> with patch:
> set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
> [  333.533878]c7  uclamp_test :
> pid=138,req_min=614,req_max=819,eff_min=614,eff_max=819
> 
> after set tg's cpu.uclamp.max = 50%，the result:
> [  430.813789]c6  uclamp_test :
> pid=138,req_min=614,req_max=819,eff_min=512,eff_max=512
> 
> case2:
> without patch:
> set task's clamp_min=614(60%), clamp_max=819(80%), the result as:
> [  169.700544]c0  uclamp_test :
> pid=137,req_min=0,req_max=209,eff_min=0,eff_max=209
> 
> after set tg's cpu.uclamp.min = 30%, tg's cpu.uclamp.max = 50%，the result:
> [  246.500634]c7  uclamp_test :
> pid=137,req_min=0,req_max=209,eff_min=307,eff_max=209
> 
> with patch:
> set task's clamp_min=0(0%), clamp_max=209(20%), the result as:
> [  169.700544]c0  uclamp_test :
> pid=137,req_min=0,req_max=209,eff_min=0,eff_max=209
> 
> after set tg's cpu.uclamp.min = 30%, tg's cpu.uclamp.max = 50%，the result:
> [  179.933868]c6  uclamp_test :
> pid=137,req_min=0,req_max=209,eff_min=307,eff_max=307

Thanks a lot for trying it out.

Cheers

--
Qais Yousef

Re: [PATCH] sched/uclamp: Fix uclamp_tg_restrict()

[Dietmar Eggemann]

On 11/06/2021 14:22, Qais Yousef wrote:
> Now cpu.uclamp.min acts as a protection, we need to make sure that the
> uclamp request of the task is within the allowed range of the cgroup,
> that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
> tg->uclamp[UCLAMP_MAX].
> 
> As reported by Xuewen [1] we can have some corner cases where there's
> inverstion between uclamp requested by task (p) and the uclamp values of

s/inverstion/inversion

[...]

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9e9a5be35cde..0318b00baa97 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
>  static inline struct uclamp_se
>  uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
>  {
> -	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> +	/* Copy by value as we could modify it */
> +	struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
>  #ifdef CONFIG_UCLAMP_TASK_GROUP
> +	unsigned int tg_min, tg_max, value;
>  
>  	/*
>  	 * Tasks in autogroups or root task group will be
>  	 * restricted by system defaults.
>  	 */
>  	if (task_group_is_autogroup(task_group(p)))
> -		return uc_req;
> +		return uc_eff;
>  	if (task_group(p) == &root_task_group)
> -		return uc_req;
> +		return uc_eff;
>  
> -	switch (clamp_id) {
> -	case UCLAMP_MIN: {
> -		struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
> -		if (uc_req.value < uc_min.value)
> -			return uc_min;
> -		break;
> -	}
> -	case UCLAMP_MAX: {
> -		struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
> -		if (uc_req.value > uc_max.value)
> -			return uc_max;
> -		break;
> -	}
> -	default:
> -		WARN_ON_ONCE(1);
> -		break;
> -	}
> +	tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
> +	tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
> +	value = uc_eff.value;
> +	value = clamp(value, tg_min, tg_max);
> +	uclamp_se_set(&uc_eff, value, false);
>  #endif
>  
> -	return uc_req;
> +	return uc_eff;
>  }

I got confused by the renaming uc_req -> uc_eff.

We have:

uclamp_eff_value()                                     (1)

  uclamp_se  uc_eff = uclamp_eff_get(p, clamp_id);     (2)

    uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id) (3)

      struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
      ....

(3) is now calling it uc_eff where (2) still uses uc_req for the return
of (3). IMHO uc_*eff* was used after the system level (
uclamp_default) have been applied.

[...]

> @@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
>  
>  	css_task_iter_start(css, 0, &it);
>  	while ((p = css_task_iter_next(&it))) {
> -		for_each_clamp_id(clamp_id) {
> -			if ((0x1 << clamp_id) & clamps)
> -				uclamp_update_active(p, clamp_id);
> -		}
> +		for_each_clamp_id(clamp_id)
> +			uclamp_update_active(p, clamp_id);
>  	}
>  	css_task_iter_end(&it);
>  }
> @@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
>  		}
>  
>  		/* Immediately update descendants RUNNABLE tasks */
> -		uclamp_update_active_tasks(css, clamps);
> +		uclamp_update_active_tasks(css);

Since we now always have to update both clamp_id's, can you not update
both under the same task_rq_lock() (in uclamp_update_active())?

Re: [PATCH] sched/uclamp: Fix uclamp_tg_restrict()

[Qais Yousef]

On 06/16/21 19:09, Dietmar Eggemann wrote:
> On 11/06/2021 14:22, Qais Yousef wrote:
> > Now cpu.uclamp.min acts as a protection, we need to make sure that the
> > uclamp request of the task is within the allowed range of the cgroup,
> > that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and
> > tg->uclamp[UCLAMP_MAX].
> > 
> > As reported by Xuewen [1] we can have some corner cases where there's
> > inverstion between uclamp requested by task (p) and the uclamp values of
> 
> s/inverstion/inversion

Fixed.

> 
> [...]
> 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 9e9a5be35cde..0318b00baa97 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1403,38 +1403,28 @@ static void uclamp_sync_util_min_rt_default(void)
> >  static inline struct uclamp_se
> >  uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
> >  {
> > -	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> > +	/* Copy by value as we could modify it */
> > +	struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
> >  #ifdef CONFIG_UCLAMP_TASK_GROUP
> > +	unsigned int tg_min, tg_max, value;
> >  
> >  	/*
> >  	 * Tasks in autogroups or root task group will be
> >  	 * restricted by system defaults.
> >  	 */
> >  	if (task_group_is_autogroup(task_group(p)))
> > -		return uc_req;
> > +		return uc_eff;
> >  	if (task_group(p) == &root_task_group)
> > -		return uc_req;
> > +		return uc_eff;
> >  
> > -	switch (clamp_id) {
> > -	case UCLAMP_MIN: {
> > -		struct uclamp_se uc_min = task_group(p)->uclamp[clamp_id];
> > -		if (uc_req.value < uc_min.value)
> > -			return uc_min;
> > -		break;
> > -	}
> > -	case UCLAMP_MAX: {
> > -		struct uclamp_se uc_max = task_group(p)->uclamp[clamp_id];
> > -		if (uc_req.value > uc_max.value)
> > -			return uc_max;
> > -		break;
> > -	}
> > -	default:
> > -		WARN_ON_ONCE(1);
> > -		break;
> > -	}
> > +	tg_min = task_group(p)->uclamp[UCLAMP_MIN].value;
> > +	tg_max = task_group(p)->uclamp[UCLAMP_MAX].value;
> > +	value = uc_eff.value;
> > +	value = clamp(value, tg_min, tg_max);
> > +	uclamp_se_set(&uc_eff, value, false);
> >  #endif
> >  
> > -	return uc_req;
> > +	return uc_eff;
> >  }
> 
> I got confused by the renaming uc_req -> uc_eff.
> 
> We have:
> 
> uclamp_eff_value()                                     (1)
> 
>   uclamp_se  uc_eff = uclamp_eff_get(p, clamp_id);     (2)
> 
>     uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id) (3)
> 
>       struct uclamp_se uc_eff = p->uclamp_req[clamp_id];
>       ....
> 
> (3) is now calling it uc_eff where (2) still uses uc_req for the return
> of (3). IMHO uc_*eff* was used after the system level (
> uclamp_default) have been applied.

Renamed it back to uc_req.

> 
> [...]
> 
> > @@ -1670,10 +1659,8 @@ uclamp_update_active_tasks(struct cgroup_subsys_state *css,
> >  
> >  	css_task_iter_start(css, 0, &it);
> >  	while ((p = css_task_iter_next(&it))) {
> > -		for_each_clamp_id(clamp_id) {
> > -			if ((0x1 << clamp_id) & clamps)
> > -				uclamp_update_active(p, clamp_id);
> > -		}
> > +		for_each_clamp_id(clamp_id)
> > +			uclamp_update_active(p, clamp_id);
> >  	}
> >  	css_task_iter_end(&it);
> >  }
> > @@ -9626,7 +9613,7 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css)
> >  		}
> >  
> >  		/* Immediately update descendants RUNNABLE tasks */
> > -		uclamp_update_active_tasks(css, clamps);
> > +		uclamp_update_active_tasks(css);
> 
> Since we now always have to update both clamp_id's, can you not update
> both under the same task_rq_lock() (in uclamp_update_active())?

Good idea. Done this

--->8---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b4e856a4335d..fdb9a109fd68 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1620,8 +1620,9 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 }

 static inline void
-uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
+uclamp_update_active(struct task_struct *p)
 {
+       enum uclamp_id clamp_id;
        struct rq_flags rf;
        struct rq *rq;

@@ -1641,9 +1642,11 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
         * affecting a valid clamp bucket, the next time it's enqueued,
         * it will already see the updated clamp bucket value.
         */
-       if (p->uclamp[clamp_id].active) {
-               uclamp_rq_dec_id(rq, p, clamp_id);
-               uclamp_rq_inc_id(rq, p, clamp_id);
+       for_each_clamp_id(clamp_id) {
+               if (p->uclamp[clamp_id].active) {
+                       uclamp_rq_dec_id(rq, p, clamp_id);
+                       uclamp_rq_inc_id(rq, p, clamp_id);
+               }
        }

        task_rq_unlock(rq, p, &rf);
@@ -1653,15 +1656,12 @@ uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
 static inline void
 uclamp_update_active_tasks(struct cgroup_subsys_state *css)
 {
-       enum uclamp_id clamp_id;
        struct css_task_iter it;
        struct task_struct *p;

        css_task_iter_start(css, 0, &it);
-       while ((p = css_task_iter_next(&it))) {
-               for_each_clamp_id(clamp_id)
-                       uclamp_update_active(p, clamp_id);
-       }
+       while ((p = css_task_iter_next(&it)))
+               uclamp_update_active(p);
        css_task_iter_end(&it);
 }

--->8---

Thanks!

--
Qais Yousef