[PATCH v1 0/2] Fix budget tracking on preemption of SCHED_QUOTA thread

[PATCH v1 0/2] Fix budget tracking on preemption of SCHED_QUOTA thread

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

Consolidated version of the patch series following the recent
discussion.

Philippe Gerum (2):
  evl/sched: core: introduce schedule out handler
  evl/sched: quota: fix budget tracking on preemption

 include/evl/sched.h       |   1 +
 include/evl/sched/quota.h |   1 +
 kernel/evl/sched/core.c   |  20 ++--
 kernel/evl/sched/quota.c  | 201 ++++++++++++++++++--------------------
 4 files changed, 110 insertions(+), 113 deletions(-)

-- 
2.54.0

[PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

Some scheduling classes may need a way to perform specific
fixup/accounting work for a thread which is being scheduled out.  We
cannot rely on the sched_pick() handler for this since the first one
to successfully pick a thread prevents other handlers down the class
hierarchy to run.

To address this issue, we introduce the sched_out() handler which is
called for the current thread when scheduled out. This handler is
invoked unconditionally when present prior to picking a new thread.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
---
 include/evl/sched.h     |  1 +
 kernel/evl/sched/core.c | 20 +++++++++++++-------
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/evl/sched.h b/include/evl/sched.h
index ae9690860146..cc824c28004b 100644
--- a/include/evl/sched.h
+++ b/include/evl/sched.h
@@ -120,6 +120,7 @@ struct evl_sched_class {
 	void (*sched_dequeue)(struct evl_thread *thread);
 	void (*sched_requeue)(struct evl_thread *thread);
 	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
+	void (*sched_out)(struct evl_thread *thread);
 	void (*sched_yield)(struct evl_thread *thread);
 	void (*sched_migrate)(struct evl_thread *thread,
 			      struct evl_rq *rq);
diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
index d1d025e06a5d..7127d4e52df9 100644
--- a/kernel/evl/sched/core.c
+++ b/kernel/evl/sched/core.c
@@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
 		evl_stop_timer(&rq->rrbtimer);
 }
 
-static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
+static __always_inline struct evl_thread *
+__pick_next_thread(struct evl_rq *rq)
 {
 	struct evl_sched_class *sched_class;
 	struct evl_thread *curr = rq->curr;
@@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
 /* rq->curr->lock + rq->lock held, hard irqs off. */
 static struct evl_thread *pick_next_thread(struct evl_rq *rq)
 {
-	struct evl_thread *next = __pick_next_thread(rq);
+	struct evl_thread *next, *prev = rq->curr;
+	struct evl_sched_class *prev_class = prev->sched_class;
 
+	if (prev_class->sched_out)
+		prev_class->sched_out(prev);
+
+	next = __pick_next_thread(rq);
+	trace_evl_pick_thread(next);
 	set_next_running(rq, next);
 
 	return next;
@@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
 		return;
 	}
 
+	prev = curr;
 	next = pick_next_thread(this_rq);
-	trace_evl_pick_thread(next);
-	if (next == curr) {
-		if (unlikely(next->state & EVL_T_ROOT)) {
+	if (next == prev) {
+		if (unlikely(prev->state & EVL_T_ROOT)) {
 			if (this_rq->local_flags & RQ_TPROXY)
 				evl_notify_proxy_tick(this_rq);
 			if (this_rq->local_flags & RQ_TDEFER)
 				evl_program_local_tick(&evl_mono_clock);
 		}
 		raw_spin_unlock(&this_rq->lock);
-		raw_spin_unlock_irqrestore(&curr->lock, flags);
+		raw_spin_unlock_irqrestore(&prev->lock, flags);
 		return;
 	}
 
-	prev = curr;
 	this_rq->curr = next;
 	leaving_inband = false;
 
-- 
2.54.0

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Jan Kiszka]

On 17.06.26 16:20, Philippe Gerum wrote:
> From: Philippe Gerum <rpm@xenomai.org>
> 
> Some scheduling classes may need a way to perform specific
> fixup/accounting work for a thread which is being scheduled out.  We
> cannot rely on the sched_pick() handler for this since the first one
> to successfully pick a thread prevents other handlers down the class
> hierarchy to run.
> 
> To address this issue, we introduce the sched_out() handler which is
> called for the current thread when scheduled out. This handler is
> invoked unconditionally when present prior to picking a new thread.
> 
> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
> ---
>  include/evl/sched.h     |  1 +
>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>  2 files changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/include/evl/sched.h b/include/evl/sched.h
> index ae9690860146..cc824c28004b 100644
> --- a/include/evl/sched.h
> +++ b/include/evl/sched.h
> @@ -120,6 +120,7 @@ struct evl_sched_class {
>  	void (*sched_dequeue)(struct evl_thread *thread);
>  	void (*sched_requeue)(struct evl_thread *thread);
>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
> +	void (*sched_out)(struct evl_thread *thread);
>  	void (*sched_yield)(struct evl_thread *thread);
>  	void (*sched_migrate)(struct evl_thread *thread,
>  			      struct evl_rq *rq);
> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
> index d1d025e06a5d..7127d4e52df9 100644
> --- a/kernel/evl/sched/core.c
> +++ b/kernel/evl/sched/core.c
> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>  		evl_stop_timer(&rq->rrbtimer);
>  }
>  
> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
> +static __always_inline struct evl_thread *
> +__pick_next_thread(struct evl_rq *rq)
>  {
>  	struct evl_sched_class *sched_class;
>  	struct evl_thread *curr = rq->curr;
> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>  {
> -	struct evl_thread *next = __pick_next_thread(rq);
> +	struct evl_thread *next, *prev = rq->curr;
> +	struct evl_sched_class *prev_class = prev->sched_class;
>  
> +	if (prev_class->sched_out)
> +		prev_class->sched_out(prev);
> +
> +	next = __pick_next_thread(rq);
> +	trace_evl_pick_thread(next);
>  	set_next_running(rq, next);
>  
>  	return next;
> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>  		return;
>  	}
>  
> +	prev = curr;
>  	next = pick_next_thread(this_rq);
> -	trace_evl_pick_thread(next);
> -	if (next == curr) {
> -		if (unlikely(next->state & EVL_T_ROOT)) {
> +	if (next == prev) {
> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>  			if (this_rq->local_flags & RQ_TPROXY)
>  				evl_notify_proxy_tick(this_rq);
>  			if (this_rq->local_flags & RQ_TDEFER)
>  				evl_program_local_tick(&evl_mono_clock);
>  		}
>  		raw_spin_unlock(&this_rq->lock);
> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>  		return;
>  	}
> - 
> -	prev = curr;

This hunk subtly look like a pure cosmetic change, without any logical
impact. If it does have one which I missed, it should be explained in
the commit message at least.

Jan

>  	this_rq->curr = next;
>  	leaving_inband = false;
>  


-- 
Siemens AG, Foundational Technologies
Linux Expert Center

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Philippe Gerum]

Jan Kiszka <jan.kiszka@siemens.com> writes:

> On 17.06.26 16:20, Philippe Gerum wrote:
>> From: Philippe Gerum <rpm@xenomai.org>
>> 
>> Some scheduling classes may need a way to perform specific
>> fixup/accounting work for a thread which is being scheduled out.  We
>> cannot rely on the sched_pick() handler for this since the first one
>> to successfully pick a thread prevents other handlers down the class
>> hierarchy to run.
>> 
>> To address this issue, we introduce the sched_out() handler which is
>> called for the current thread when scheduled out. This handler is
>> invoked unconditionally when present prior to picking a new thread.
>> 
>> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
>> ---
>>  include/evl/sched.h     |  1 +
>>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>>  2 files changed, 14 insertions(+), 7 deletions(-)
>> 
>> diff --git a/include/evl/sched.h b/include/evl/sched.h
>> index ae9690860146..cc824c28004b 100644
>> --- a/include/evl/sched.h
>> +++ b/include/evl/sched.h
>> @@ -120,6 +120,7 @@ struct evl_sched_class {
>>  	void (*sched_dequeue)(struct evl_thread *thread);
>>  	void (*sched_requeue)(struct evl_thread *thread);
>>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
>> +	void (*sched_out)(struct evl_thread *thread);
>>  	void (*sched_yield)(struct evl_thread *thread);
>>  	void (*sched_migrate)(struct evl_thread *thread,
>>  			      struct evl_rq *rq);
>> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
>> index d1d025e06a5d..7127d4e52df9 100644
>> --- a/kernel/evl/sched/core.c
>> +++ b/kernel/evl/sched/core.c
>> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>>  		evl_stop_timer(&rq->rrbtimer);
>>  }
>>  
>> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>> +static __always_inline struct evl_thread *
>> +__pick_next_thread(struct evl_rq *rq)
>>  {
>>  	struct evl_sched_class *sched_class;
>>  	struct evl_thread *curr = rq->curr;
>> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>>  {
>> -	struct evl_thread *next = __pick_next_thread(rq);
>> +	struct evl_thread *next, *prev = rq->curr;
>> +	struct evl_sched_class *prev_class = prev->sched_class;
>>  
>> +	if (prev_class->sched_out)
>> +		prev_class->sched_out(prev);
>> +
>> +	next = __pick_next_thread(rq);
>> +	trace_evl_pick_thread(next);
>>  	set_next_running(rq, next);
>>  
>>  	return next;
>> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>>  		return;
>>  	}
>>  
>> +	prev = curr;
>>  	next = pick_next_thread(this_rq);
>> -	trace_evl_pick_thread(next);
>> -	if (next == curr) {
>> -		if (unlikely(next->state & EVL_T_ROOT)) {
>> +	if (next == prev) {
>> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>>  			if (this_rq->local_flags & RQ_TPROXY)
>>  				evl_notify_proxy_tick(this_rq);
>>  			if (this_rq->local_flags & RQ_TDEFER)
>>  				evl_program_local_tick(&evl_mono_clock);
>>  		}
>>  		raw_spin_unlock(&this_rq->lock);
>> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
>> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>>  		return;
>>  	}
>> - 
>> -	prev = curr;
>
> This hunk subtly look like a pure cosmetic change, without any logical
> impact. If it does have one which I missed, it should be explained in
> the commit message at least.
>

It has none, as mentioned earlier in a previous post. The point of this
change is to clarify the naming, introducing 'prev' as an alias to
'curr' in the swap sequence. So there is no point in documenting this.

-- 
Philippe.

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Jan Kiszka]

On 18.06.26 09:44, Philippe Gerum wrote:
> Jan Kiszka <jan.kiszka@siemens.com> writes:
> 
>> On 17.06.26 16:20, Philippe Gerum wrote:
>>> From: Philippe Gerum <rpm@xenomai.org>
>>>
>>> Some scheduling classes may need a way to perform specific
>>> fixup/accounting work for a thread which is being scheduled out.  We
>>> cannot rely on the sched_pick() handler for this since the first one
>>> to successfully pick a thread prevents other handlers down the class
>>> hierarchy to run.
>>>
>>> To address this issue, we introduce the sched_out() handler which is
>>> called for the current thread when scheduled out. This handler is
>>> invoked unconditionally when present prior to picking a new thread.
>>>
>>> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
>>> ---
>>>  include/evl/sched.h     |  1 +
>>>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>>>  2 files changed, 14 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/evl/sched.h b/include/evl/sched.h
>>> index ae9690860146..cc824c28004b 100644
>>> --- a/include/evl/sched.h
>>> +++ b/include/evl/sched.h
>>> @@ -120,6 +120,7 @@ struct evl_sched_class {
>>>  	void (*sched_dequeue)(struct evl_thread *thread);
>>>  	void (*sched_requeue)(struct evl_thread *thread);
>>>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
>>> +	void (*sched_out)(struct evl_thread *thread);
>>>  	void (*sched_yield)(struct evl_thread *thread);
>>>  	void (*sched_migrate)(struct evl_thread *thread,
>>>  			      struct evl_rq *rq);
>>> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
>>> index d1d025e06a5d..7127d4e52df9 100644
>>> --- a/kernel/evl/sched/core.c
>>> +++ b/kernel/evl/sched/core.c
>>> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>>>  		evl_stop_timer(&rq->rrbtimer);
>>>  }
>>>  
>>> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>> +static __always_inline struct evl_thread *
>>> +__pick_next_thread(struct evl_rq *rq)
>>>  {
>>>  	struct evl_sched_class *sched_class;
>>>  	struct evl_thread *curr = rq->curr;
>>> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>>>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>>>  {
>>> -	struct evl_thread *next = __pick_next_thread(rq);
>>> +	struct evl_thread *next, *prev = rq->curr;
>>> +	struct evl_sched_class *prev_class = prev->sched_class;
>>>  
>>> +	if (prev_class->sched_out)
>>> +		prev_class->sched_out(prev);
>>> +
>>> +	next = __pick_next_thread(rq);
>>> +	trace_evl_pick_thread(next);
>>>  	set_next_running(rq, next);
>>>  
>>>  	return next;
>>> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>>>  		return;
>>>  	}
>>>  
>>> +	prev = curr;
>>>  	next = pick_next_thread(this_rq);
>>> -	trace_evl_pick_thread(next);
>>> -	if (next == curr) {
>>> -		if (unlikely(next->state & EVL_T_ROOT)) {
>>> +	if (next == prev) {
>>> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>>>  			if (this_rq->local_flags & RQ_TPROXY)
>>>  				evl_notify_proxy_tick(this_rq);
>>>  			if (this_rq->local_flags & RQ_TDEFER)
>>>  				evl_program_local_tick(&evl_mono_clock);
>>>  		}
>>>  		raw_spin_unlock(&this_rq->lock);
>>> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
>>> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>>>  		return;
>>>  	}
>>> - 
>>> -	prev = curr;
>>
>> This hunk subtly look like a pure cosmetic change, without any logical
>> impact. If it does have one which I missed, it should be explained in
>> the commit message at least.
>>
> 
> It has none, as mentioned earlier in a previous post. The point of this
> change is to clarify the naming, introducing 'prev' as an alias to
> 'curr' in the swap sequence. So there is no point in documenting this.
> 

Again, it is suboptimal style to fold refactorings into logical code
changes. If you split this up into two commits, properly explaining the
purpose of that renaming, things become readable to 3rd parties.

Jan

-- 
Siemens AG, Foundational Technologies
Linux Expert Center

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Philippe Gerum]

Jan Kiszka <jan.kiszka@siemens.com> writes:

> On 18.06.26 09:44, Philippe Gerum wrote:
>> Jan Kiszka <jan.kiszka@siemens.com> writes:
>> 
>>> On 17.06.26 16:20, Philippe Gerum wrote:
>>>> From: Philippe Gerum <rpm@xenomai.org>
>>>>
>>>> Some scheduling classes may need a way to perform specific
>>>> fixup/accounting work for a thread which is being scheduled out.  We
>>>> cannot rely on the sched_pick() handler for this since the first one
>>>> to successfully pick a thread prevents other handlers down the class
>>>> hierarchy to run.
>>>>
>>>> To address this issue, we introduce the sched_out() handler which is
>>>> called for the current thread when scheduled out. This handler is
>>>> invoked unconditionally when present prior to picking a new thread.
>>>>
>>>> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
>>>> ---
>>>>  include/evl/sched.h     |  1 +
>>>>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>>>>  2 files changed, 14 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/include/evl/sched.h b/include/evl/sched.h
>>>> index ae9690860146..cc824c28004b 100644
>>>> --- a/include/evl/sched.h
>>>> +++ b/include/evl/sched.h
>>>> @@ -120,6 +120,7 @@ struct evl_sched_class {
>>>>  	void (*sched_dequeue)(struct evl_thread *thread);
>>>>  	void (*sched_requeue)(struct evl_thread *thread);
>>>>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
>>>> +	void (*sched_out)(struct evl_thread *thread);
>>>>  	void (*sched_yield)(struct evl_thread *thread);
>>>>  	void (*sched_migrate)(struct evl_thread *thread,
>>>>  			      struct evl_rq *rq);
>>>> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
>>>> index d1d025e06a5d..7127d4e52df9 100644
>>>> --- a/kernel/evl/sched/core.c
>>>> +++ b/kernel/evl/sched/core.c
>>>> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>>>>  		evl_stop_timer(&rq->rrbtimer);
>>>>  }
>>>>  
>>>> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>> +static __always_inline struct evl_thread *
>>>> +__pick_next_thread(struct evl_rq *rq)
>>>>  {
>>>>  	struct evl_sched_class *sched_class;
>>>>  	struct evl_thread *curr = rq->curr;
>>>> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>>>>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>>>>  {
>>>> -	struct evl_thread *next = __pick_next_thread(rq);
>>>> +	struct evl_thread *next, *prev = rq->curr;
>>>> +	struct evl_sched_class *prev_class = prev->sched_class;
>>>>  
>>>> +	if (prev_class->sched_out)
>>>> +		prev_class->sched_out(prev);
>>>> +
>>>> +	next = __pick_next_thread(rq);
>>>> +	trace_evl_pick_thread(next);
>>>>  	set_next_running(rq, next);
>>>>  
>>>>  	return next;
>>>> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>>>>  		return;
>>>>  	}
>>>>  
>>>> +	prev = curr;
>>>>  	next = pick_next_thread(this_rq);
>>>> -	trace_evl_pick_thread(next);
>>>> -	if (next == curr) {
>>>> -		if (unlikely(next->state & EVL_T_ROOT)) {
>>>> +	if (next == prev) {
>>>> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>>>>  			if (this_rq->local_flags & RQ_TPROXY)
>>>>  				evl_notify_proxy_tick(this_rq);
>>>>  			if (this_rq->local_flags & RQ_TDEFER)
>>>>  				evl_program_local_tick(&evl_mono_clock);
>>>>  		}
>>>>  		raw_spin_unlock(&this_rq->lock);
>>>> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
>>>> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>>>>  		return;
>>>>  	}
>>>> - 
>>>> -	prev = curr;
>>>
>>> This hunk subtly look like a pure cosmetic change, without any logical
>>> impact. If it does have one which I missed, it should be explained in
>>> the commit message at least.
>>>
>> 
>> It has none, as mentioned earlier in a previous post. The point of this
>> change is to clarify the naming, introducing 'prev' as an alias to
>> 'curr' in the swap sequence. So there is no point in documenting this.
>> 
>
> Again, it is suboptimal style to fold refactorings into logical code
> changes. If you split this up into two commits, properly explaining the
> purpose of that renaming, things become readable to 3rd parties.
>

I understand your point of view, I simply disagree with the scope of the
requirement as you state it. So let's move on.

-- 
Philippe.

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Philippe Gerum]

Philippe Gerum <rpm@xenomai.org> writes:

> Jan Kiszka <jan.kiszka@siemens.com> writes:
>
>> On 18.06.26 09:44, Philippe Gerum wrote:
>>> Jan Kiszka <jan.kiszka@siemens.com> writes:
>>> 
>>>> On 17.06.26 16:20, Philippe Gerum wrote:
>>>>> From: Philippe Gerum <rpm@xenomai.org>
>>>>>
>>>>> Some scheduling classes may need a way to perform specific
>>>>> fixup/accounting work for a thread which is being scheduled out.  We
>>>>> cannot rely on the sched_pick() handler for this since the first one
>>>>> to successfully pick a thread prevents other handlers down the class
>>>>> hierarchy to run.
>>>>>
>>>>> To address this issue, we introduce the sched_out() handler which is
>>>>> called for the current thread when scheduled out. This handler is
>>>>> invoked unconditionally when present prior to picking a new thread.
>>>>>
>>>>> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
>>>>> ---
>>>>>  include/evl/sched.h     |  1 +
>>>>>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>>>>>  2 files changed, 14 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/include/evl/sched.h b/include/evl/sched.h
>>>>> index ae9690860146..cc824c28004b 100644
>>>>> --- a/include/evl/sched.h
>>>>> +++ b/include/evl/sched.h
>>>>> @@ -120,6 +120,7 @@ struct evl_sched_class {
>>>>>  	void (*sched_dequeue)(struct evl_thread *thread);
>>>>>  	void (*sched_requeue)(struct evl_thread *thread);
>>>>>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
>>>>> +	void (*sched_out)(struct evl_thread *thread);
>>>>>  	void (*sched_yield)(struct evl_thread *thread);
>>>>>  	void (*sched_migrate)(struct evl_thread *thread,
>>>>>  			      struct evl_rq *rq);
>>>>> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
>>>>> index d1d025e06a5d..7127d4e52df9 100644
>>>>> --- a/kernel/evl/sched/core.c
>>>>> +++ b/kernel/evl/sched/core.c
>>>>> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>>>>>  		evl_stop_timer(&rq->rrbtimer);
>>>>>  }
>>>>>  
>>>>> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>>> +static __always_inline struct evl_thread *
>>>>> +__pick_next_thread(struct evl_rq *rq)
>>>>>  {
>>>>>  	struct evl_sched_class *sched_class;
>>>>>  	struct evl_thread *curr = rq->curr;
>>>>> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>>>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>>>>>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>>>>>  {
>>>>> -	struct evl_thread *next = __pick_next_thread(rq);
>>>>> +	struct evl_thread *next, *prev = rq->curr;
>>>>> +	struct evl_sched_class *prev_class = prev->sched_class;
>>>>>  
>>>>> +	if (prev_class->sched_out)
>>>>> +		prev_class->sched_out(prev);
>>>>> +
>>>>> +	next = __pick_next_thread(rq);
>>>>> +	trace_evl_pick_thread(next);
>>>>>  	set_next_running(rq, next);
>>>>>  
>>>>>  	return next;
>>>>> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>>>>>  		return;
>>>>>  	}
>>>>>  
>>>>> +	prev = curr;
>>>>>  	next = pick_next_thread(this_rq);
>>>>> -	trace_evl_pick_thread(next);
>>>>> -	if (next == curr) {
>>>>> -		if (unlikely(next->state & EVL_T_ROOT)) {
>>>>> +	if (next == prev) {
>>>>> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>>>>>  			if (this_rq->local_flags & RQ_TPROXY)
>>>>>  				evl_notify_proxy_tick(this_rq);
>>>>>  			if (this_rq->local_flags & RQ_TDEFER)
>>>>>  				evl_program_local_tick(&evl_mono_clock);
>>>>>  		}
>>>>>  		raw_spin_unlock(&this_rq->lock);
>>>>> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
>>>>> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>>>>>  		return;
>>>>>  	}
>>>>> - 
>>>>> -	prev = curr;
>>>>
>>>> This hunk subtly look like a pure cosmetic change, without any logical
>>>> impact. If it does have one which I missed, it should be explained in
>>>> the commit message at least.
>>>>
>>> 
>>> It has none, as mentioned earlier in a previous post. The point of this
>>> change is to clarify the naming, introducing 'prev' as an alias to
>>> 'curr' in the swap sequence. So there is no point in documenting this.
>>> 
>>
>> Again, it is suboptimal style to fold refactorings into logical code
>> changes. If you split this up into two commits, properly explaining the
>> purpose of that renaming, things become readable to 3rd parties.
>>
>
> I understand your point of view, I simply disagree with the scope of the
> requirement as you state it. So let's move on.

Meanwhile, I just received a second opinion stating that this change
seems vaguely troubling, raising interior alarm bells. I must be the
only one to find it trivial, so ok. I'll split that, moving it to a
separate patch.

-- 
Philippe.

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Jan Kiszka]

On 18.06.26 09:44, Philippe Gerum wrote:
> Jan Kiszka <jan.kiszka@siemens.com> writes:
> 
>> On 17.06.26 16:20, Philippe Gerum wrote:
>>> From: Philippe Gerum <rpm@xenomai.org>
>>>
>>> Some scheduling classes may need a way to perform specific
>>> fixup/accounting work for a thread which is being scheduled out.  We
>>> cannot rely on the sched_pick() handler for this since the first one
>>> to successfully pick a thread prevents other handlers down the class
>>> hierarchy to run.
>>>
>>> To address this issue, we introduce the sched_out() handler which is
>>> called for the current thread when scheduled out. This handler is
>>> invoked unconditionally when present prior to picking a new thread.
>>>
>>> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
>>> ---
>>>  include/evl/sched.h     |  1 +
>>>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>>>  2 files changed, 14 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/evl/sched.h b/include/evl/sched.h
>>> index ae9690860146..cc824c28004b 100644
>>> --- a/include/evl/sched.h
>>> +++ b/include/evl/sched.h
>>> @@ -120,6 +120,7 @@ struct evl_sched_class {
>>>  	void (*sched_dequeue)(struct evl_thread *thread);
>>>  	void (*sched_requeue)(struct evl_thread *thread);
>>>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
>>> +	void (*sched_out)(struct evl_thread *thread);
>>>  	void (*sched_yield)(struct evl_thread *thread);
>>>  	void (*sched_migrate)(struct evl_thread *thread,
>>>  			      struct evl_rq *rq);
>>> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
>>> index d1d025e06a5d..7127d4e52df9 100644
>>> --- a/kernel/evl/sched/core.c
>>> +++ b/kernel/evl/sched/core.c
>>> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>>>  		evl_stop_timer(&rq->rrbtimer);
>>>  }
>>>  
>>> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>> +static __always_inline struct evl_thread *
>>> +__pick_next_thread(struct evl_rq *rq)
>>>  {
>>>  	struct evl_sched_class *sched_class;
>>>  	struct evl_thread *curr = rq->curr;
>>> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>>>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>>>  {
>>> -	struct evl_thread *next = __pick_next_thread(rq);
>>> +	struct evl_thread *next, *prev = rq->curr;
>>> +	struct evl_sched_class *prev_class = prev->sched_class;
>>>  
>>> +	if (prev_class->sched_out)
>>> +		prev_class->sched_out(prev);
>>> +
>>> +	next = __pick_next_thread(rq);
>>> +	trace_evl_pick_thread(next);
>>>  	set_next_running(rq, next);
>>>  
>>>  	return next;
>>> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>>>  		return;
>>>  	}
>>>  
>>> +	prev = curr;
>>>  	next = pick_next_thread(this_rq);
>>> -	trace_evl_pick_thread(next);
>>> -	if (next == curr) {
>>> -		if (unlikely(next->state & EVL_T_ROOT)) {
>>> +	if (next == prev) {
>>> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>>>  			if (this_rq->local_flags & RQ_TPROXY)
>>>  				evl_notify_proxy_tick(this_rq);
>>>  			if (this_rq->local_flags & RQ_TDEFER)
>>>  				evl_program_local_tick(&evl_mono_clock);
>>>  		}
>>>  		raw_spin_unlock(&this_rq->lock);
>>> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
>>> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>>>  		return;
>>>  	}
>>> - 
>>> -	prev = curr;
>>
>> This hunk subtly look like a pure cosmetic change, without any logical
>> impact. If it does have one which I missed, it should be explained in
>> the commit message at least.
>>
> 
> It has none, as mentioned earlier in a previous post. The point of this
> change is to clarify the naming, introducing 'prev' as an alias to
> 'curr' in the swap sequence. So there is no point in documenting this.
> 

BTW, I would not make lock/unlock work against different variables
names, though they carry identical pointers. That is more confusing than
the current code.

Jan

-- 
Siemens AG, Foundational Technologies
Linux Expert Center

Re: [PATCH v1 1/2] evl/sched: core: introduce schedule out handler

[Philippe Gerum]

Jan Kiszka <jan.kiszka@siemens.com> writes:

> On 18.06.26 09:44, Philippe Gerum wrote:
>> Jan Kiszka <jan.kiszka@siemens.com> writes:
>> 
>>> On 17.06.26 16:20, Philippe Gerum wrote:
>>>> From: Philippe Gerum <rpm@xenomai.org>
>>>>
>>>> Some scheduling classes may need a way to perform specific
>>>> fixup/accounting work for a thread which is being scheduled out.  We
>>>> cannot rely on the sched_pick() handler for this since the first one
>>>> to successfully pick a thread prevents other handlers down the class
>>>> hierarchy to run.
>>>>
>>>> To address this issue, we introduce the sched_out() handler which is
>>>> called for the current thread when scheduled out. This handler is
>>>> invoked unconditionally when present prior to picking a new thread.
>>>>
>>>> Signed-off-by: Philippe Gerum <rpm@xenomai.org>
>>>> ---
>>>>  include/evl/sched.h     |  1 +
>>>>  kernel/evl/sched/core.c | 20 +++++++++++++-------
>>>>  2 files changed, 14 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/include/evl/sched.h b/include/evl/sched.h
>>>> index ae9690860146..cc824c28004b 100644
>>>> --- a/include/evl/sched.h
>>>> +++ b/include/evl/sched.h
>>>> @@ -120,6 +120,7 @@ struct evl_sched_class {
>>>>  	void (*sched_dequeue)(struct evl_thread *thread);
>>>>  	void (*sched_requeue)(struct evl_thread *thread);
>>>>  	struct evl_thread *(*sched_pick)(struct evl_rq *rq);
>>>> +	void (*sched_out)(struct evl_thread *thread);
>>>>  	void (*sched_yield)(struct evl_thread *thread);
>>>>  	void (*sched_migrate)(struct evl_thread *thread,
>>>>  			      struct evl_rq *rq);
>>>> diff --git a/kernel/evl/sched/core.c b/kernel/evl/sched/core.c
>>>> index d1d025e06a5d..7127d4e52df9 100644
>>>> --- a/kernel/evl/sched/core.c
>>>> +++ b/kernel/evl/sched/core.c
>>>> @@ -773,7 +773,8 @@ static inline void set_next_running(struct evl_rq *rq,
>>>>  		evl_stop_timer(&rq->rrbtimer);
>>>>  }
>>>>  
>>>> -static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>> +static __always_inline struct evl_thread *
>>>> +__pick_next_thread(struct evl_rq *rq)
>>>>  {
>>>>  	struct evl_sched_class *sched_class;
>>>>  	struct evl_thread *curr = rq->curr;
>>>> @@ -821,8 +822,14 @@ static struct evl_thread *__pick_next_thread(struct evl_rq *rq)
>>>>  /* rq->curr->lock + rq->lock held, hard irqs off. */
>>>>  static struct evl_thread *pick_next_thread(struct evl_rq *rq)
>>>>  {
>>>> -	struct evl_thread *next = __pick_next_thread(rq);
>>>> +	struct evl_thread *next, *prev = rq->curr;
>>>> +	struct evl_sched_class *prev_class = prev->sched_class;
>>>>  
>>>> +	if (prev_class->sched_out)
>>>> +		prev_class->sched_out(prev);
>>>> +
>>>> +	next = __pick_next_thread(rq);
>>>> +	trace_evl_pick_thread(next);
>>>>  	set_next_running(rq, next);
>>>>  
>>>>  	return next;
>>>> @@ -972,21 +979,20 @@ void __evl_schedule(void) /* oob or/and hard irqs off (CPU migration-safe) */
>>>>  		return;
>>>>  	}
>>>>  
>>>> +	prev = curr;
>>>>  	next = pick_next_thread(this_rq);
>>>> -	trace_evl_pick_thread(next);
>>>> -	if (next == curr) {
>>>> -		if (unlikely(next->state & EVL_T_ROOT)) {
>>>> +	if (next == prev) {
>>>> +		if (unlikely(prev->state & EVL_T_ROOT)) {
>>>>  			if (this_rq->local_flags & RQ_TPROXY)
>>>>  				evl_notify_proxy_tick(this_rq);
>>>>  			if (this_rq->local_flags & RQ_TDEFER)
>>>>  				evl_program_local_tick(&evl_mono_clock);
>>>>  		}
>>>>  		raw_spin_unlock(&this_rq->lock);
>>>> -		raw_spin_unlock_irqrestore(&curr->lock, flags);
>>>> +		raw_spin_unlock_irqrestore(&prev->lock, flags);
>>>>  		return;
>>>>  	}
>>>> - 
>>>> -	prev = curr;
>>>
>>> This hunk subtly look like a pure cosmetic change, without any logical
>>> impact. If it does have one which I missed, it should be explained in
>>> the commit message at least.
>>>
>> 
>> It has none, as mentioned earlier in a previous post. The point of this
>> change is to clarify the naming, introducing 'prev' as an alias to
>> 'curr' in the swap sequence. So there is no point in documenting this.
>> 
>
> BTW, I would not make lock/unlock work against different variables
> names, though they carry identical pointers. That is more confusing than
> the current code.
>

Yes, that point is valid. But in that case, there is no point in even
clarifying the rest either. Ok, dropping the whole thing together.

-- 
Philippe.

[PATCH v1 2/2] evl/sched: quota: fix budget tracking on preemption

[Philippe Gerum]

From: Philippe Gerum <rpm@xenomai.org>

Upon preemption of a SCHED_QUOTA thread by a SCHED_FIFO one, the
runtime budget of the former is inaccurately tracked. This is due to
the fifo->sched_pick() handler returning a valid thread, which
prevents the quota->sched_pick() handler from being called. As a
result, the last runtime period of the outgoing thread is not
accounted for.

To fix this issue, we use the recently introduced sched_out() handler
to update the remaining budget of preempted threads appropriately.  In
addition, the SCHED_QUOTA gains its own runnable thread queue, no
longer piggybacks off the SCHED_FIFO queue (no functional change).

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
---
 include/evl/sched/quota.h |   1 +
 kernel/evl/sched/quota.c  | 201 ++++++++++++++++++--------------------
 2 files changed, 96 insertions(+), 106 deletions(-)

diff --git a/include/evl/sched/quota.h b/include/evl/sched/quota.h
index dfe3b7390958..dc8416645da8 100644
--- a/include/evl/sched/quota.h
+++ b/include/evl/sched/quota.h
@@ -40,6 +40,7 @@ struct evl_quota_group {
 
 struct evl_sched_quota {
 	ktime_t period;
+	struct evl_sched_queue runnable;
 	struct evl_timer refill_timer;
 	struct evl_timer limit_timer;
 	struct list_head groups;
diff --git a/kernel/evl/sched/quota.c b/kernel/evl/sched/quota.c
index 0829da711a66..8f1321d46cac 100644
--- a/kernel/evl/sched/quota.c
+++ b/kernel/evl/sched/quota.c
@@ -12,45 +12,35 @@
 #include <uapi/evl/sched-abi.h>
 
 /*
- * With this policy, each per-CPU runqueue maintains a list of active
- * thread groups for the sched_fifo class.
- *
- * Each time a thread is picked from the runqueue, we check whether we
- * still have budget for running it, looking at the group it belongs
- * to. If so, a timer is armed to elapse when that group has no more
- * budget, would the incoming thread run unpreempted until then
- * (i.e. evl_quota->limit_timer).
+ * Each time a thread is picked from the ->runnable queue, we check
+ * whether the group it belongs to still has runtime budget.  If so, a
+ * timer is armed to fire when that group has no more budget, would
+ * the incoming thread run unpreempted until then
+ * (i.e. quota->limit_timer).
  *
  * Otherwise, if no budget remains in the group for running the
  * candidate thread, we move the latter to a local expiry queue
  * maintained by the group. This process is done on the fly as we pull
- * from the runqueue.
+ * from the ->runnable queue.
  *
- * Updating the remaining budget is done each time the EVL core asks
- * for replacing the current thread with the next runnable one,
- * i.e. evl_quota_pick(). There we charge the elapsed run time of the
- * outgoing thread to the relevant group, and conversely, we check
- * whether the incoming thread has budget.
+ * Updating the remaining budget is done each time the EVL core
+ * schedules out a thread undergoing the quota scheduling policy,
  *
- * Finally, a per-CPU timer (evl_quota->refill_timer) periodically
- * ticks in the background, in accordance to the defined quota
- * interval. Thread group budgets get replenished by its handler in
- * accordance to their respective share, pushing all expired threads
- * back to the run queue in the same move.
+ * Finally, a per-CPU timer (quota->refill_timer) periodically ticks
+ * in the background, in accordance to the defined quota interval,
+ * replenishing per-group budgets, pushing all expired threads back to
+ * the quota ->runqueue too.
  *
- * NOTE: since the core logic enforcing the budget entirely happens in
- * evl_quota_pick(), applying a budget change can be done as simply as
- * forcing the rescheduling procedure to be invoked asap. As a result
- * of this, the EVL core will ask for the next thread to run, which
- * means calling evl_quota_pick() eventually.
+ * NOTE: forcing a call to the rescheduling procedure is enoiugh to
+ * apply a budget change.
  *
- * CAUTION: evl_quota_group->nr_active does count both the threads
- * from that group linked to the sched_fifo runqueue, _and_ the
- * threads moved to the local expiry queue. As a matter of fact, the
- * expired threads - those for which we consumed all the per-group
- * budget - are still seen as runnable (i.e. not blocked/suspended) by
- * the EVL core. This only means that the SCHED_QUOTA policy won't
- * pick them until the corresponding budget is replenished.
+ * CAUTION: quota_group->nr_active does count both the threads from
+ * that group linked to the runnable queue, _and_ the threads moved to
+ * the local expiry queue. As a matter of fact, the expired threads -
+ * those for which we consumed all the per-group budget - are still
+ * seen as runnable (i.e. not blocked/suspended) by the EVL core. This
+ * only means that the SCHED_QUOTA policy won't pick them until the
+ * corresponding budget is replenished.
  */
 
 #define MAX_QUOTA_GROUPS  1024
@@ -61,15 +51,19 @@ static DECLARE_BITMAP(group_map, MAX_QUOTA_GROUPS);
 
 static LIST_HEAD(group_list);
 
-static inline bool thread_on_quota(struct evl_thread *thread,
-				struct evl_quota_group *tg)
+static inline bool current_on_quota(struct evl_quota_group *tg)
 {
-	/*
-	 * Check whether @thread is running on some CPU, and belongs
-	 * to quota group @tg.
-	 */
-	return thread->quota == tg &&
-		!(thread->state & (EVL_T_READY|EVL_THREAD_BLOCK_MASK));
+	struct evl_rq *rq = tg->rq;
+	struct evl_thread *curr = rq->curr;
+	struct evl_sched_quota *qs = &rq->quota;
+
+	if (curr->quota != tg)
+		return false;
+
+	if (curr->state & (EVL_T_READY|EVL_T_KICKED|EVL_THREAD_BLOCK_MASK))
+		return false;
+
+	return evl_timer_is_running(&qs->limit_timer);
 }
 
 static inline bool group_is_active(struct evl_quota_group *tg)
@@ -82,7 +76,7 @@ static inline bool group_is_active(struct evl_quota_group *tg)
 	 * runqueue, in which case tg->nr_active already accounted for
 	 * it.
 	 */
-	return thread_on_quota(tg->rq->curr, tg);
+	return current_on_quota(tg);
 }
 
 static inline void replenish_budget(struct evl_sched_quota *qs,
@@ -134,10 +128,10 @@ static inline void replenish_budget(struct evl_sched_quota *qs,
 	} else if (tg->run_credit) {
 		credit = ktime_sub(tg->quota_peak, budget);
 		/* Consume the accumulated credit. */
-		if (tg->run_credit >= credit)
+		if (tg->run_credit >= credit) {
 			tg->run_credit =
 				ktime_sub(tg->run_credit, credit);
-		else {
+		} else {
 			credit = tg->run_credit;
 			tg->run_credit = 0;
 		}
@@ -150,8 +144,8 @@ static inline void replenish_budget(struct evl_sched_quota *qs,
 
 static void quota_refill_handler(struct evl_timer *timer) /* oob stage stalled */
 {
-	struct evl_quota_group *tg;
 	struct evl_thread *thread, *tmp;
+	struct evl_quota_group *tg;
 	struct evl_sched_quota *qs;
 	struct evl_rq *rq;
 
@@ -167,7 +161,7 @@ static void quota_refill_handler(struct evl_timer *timer) /* oob stage stalled *
 		if (tg->run_budget == 0 || list_empty(&tg->expired))
 			continue;
 		/*
-		 * For each group living on this CPU, move all expired
+		 * For each group pinned on this CPU, move all expired
 		 * threads back to the runqueue. Since those threads
 		 * were moved out of the runqueue as we were
 		 * considering them for execution, we push them back
@@ -178,7 +172,7 @@ static void quota_refill_handler(struct evl_timer *timer) /* oob stage stalled *
 		list_for_each_entry_safe_reverse(thread, tmp,
 						&tg->expired, quota_expired) {
 			list_del_init(&thread->quota_expired);
-			evl_add_schedq(&rq->fifo.runnable, thread);
+			evl_add_schedq(&qs->runnable, thread);
 		}
 	}
 
@@ -195,7 +189,7 @@ static void quota_limit_handler(struct evl_timer *timer) /* oob stage stalled */
 	/*
 	 * Force a rescheduling on the return path of the current
 	 * interrupt, so that the budget is re-evaluated for the
-	 * current group in evl_quota_pick().
+	 * current group in quota_pick().
 	 */
 	raw_spin_lock(&rq->lock);
 	evl_set_self_resched(rq);
@@ -221,6 +215,7 @@ static void quota_init(struct evl_rq *rq)
 {
 	struct evl_sched_quota *qs = &rq->quota;
 
+	evl_init_schedq(&qs->runnable);
 	qs->period = quota_period;
 	INIT_LIST_HEAD(&qs->groups);
 
@@ -337,8 +332,8 @@ static void quota_forget(struct evl_thread *thread)
 
 static void quota_kick(struct evl_thread *thread)
 {
+	struct evl_sched_quota *qs = &thread->rq->quota;
 	struct evl_quota_group *tg = thread->quota;
-	struct evl_rq *rq = thread->rq;
 
 	/*
 	 * Allow a kicked thread to be elected for running until it
@@ -347,7 +342,7 @@ static void quota_kick(struct evl_thread *thread)
 	 */
 	if (tg->run_budget == 0 && !list_empty(&thread->quota_expired)) {
 		list_del_init(&thread->quota_expired);
-		evl_add_schedq_tail(&rq->fifo.runnable, thread);
+		evl_add_schedq_tail(&qs->runnable, thread);
 	}
 }
 
@@ -358,79 +353,83 @@ static inline int thread_is_runnable(struct evl_thread *thread)
 
 static void quota_enqueue(struct evl_thread *thread)
 {
+	struct evl_sched_quota *qs = &thread->rq->quota;
 	struct evl_quota_group *tg = thread->quota;
-	struct evl_rq *rq = thread->rq;
 
 	if (!thread_is_runnable(thread))
 		list_add_tail(&thread->quota_expired, &tg->expired);
 	else
-		evl_add_schedq_tail(&rq->fifo.runnable, thread);
+		evl_add_schedq_tail(&qs->runnable, thread);
 
 	tg->nr_active++;
 }
 
 static void quota_dequeue(struct evl_thread *thread)
 {
+	struct evl_sched_quota *qs = &thread->rq->quota;
 	struct evl_quota_group *tg = thread->quota;
-	struct evl_rq *rq = thread->rq;
 
 	if (!list_empty(&thread->quota_expired))
 		list_del_init(&thread->quota_expired);
 	else
-		evl_del_schedq(&rq->fifo.runnable, thread);
+		evl_del_schedq(&qs->runnable, thread);
 
 	tg->nr_active--;
 }
 
 static void quota_requeue(struct evl_thread *thread)
 {
+	struct evl_sched_quota *qs = &thread->rq->quota;
 	struct evl_quota_group *tg = thread->quota;
-	struct evl_rq *rq = thread->rq;
 
 	if (!thread_is_runnable(thread))
 		list_add(&thread->quota_expired, &tg->expired);
 	else
-		evl_add_schedq(&rq->fifo.runnable, thread);
+		evl_add_schedq(&qs->runnable, thread);
 
 	tg->nr_active++;
 }
 
-static struct evl_thread *quota_pick(struct evl_rq *rq)
+static void quota_out(struct evl_thread *thread)
 {
-	struct evl_thread *next, *curr = rq->curr;
-	struct evl_sched_quota *qs = &rq->quota;
-	struct evl_quota_group *otg, *tg;
-	ktime_t now, elapsed;
+	struct evl_sched_quota *qs = &thread->rq->quota;
+	struct evl_quota_group *tg = thread->quota;
+	ktime_t now, consumed;
+
+	/* Timer off means that we are not tracking quota. */
+	if (!evl_timer_is_running(&qs->limit_timer))
+		return;
 
-	now = evl_ktime_monotonic();
-	otg = curr->quota;
-	if (otg == NULL)
-		goto pick;
 	/*
 	 * Charge the time consumed by the outgoing thread to the
 	 * group it belongs to.
 	 */
-	elapsed = ktime_sub(now, otg->run_start);
-	if (elapsed < otg->run_budget)
-		otg->run_budget = ktime_sub(otg->run_budget, elapsed);
-	else
-		otg->run_budget = 0;
+	now = evl_ktime_monotonic();
+	consumed = ktime_sub(now, tg->run_start);
+	if (consumed < tg->run_budget) {
+		tg->run_start = now;
+		tg->run_budget = ktime_sub(tg->run_budget, consumed);
+	} else {
+		tg->run_budget = 0;
+		evl_stop_timer(&qs->limit_timer);
+	}
+}
+
+static struct evl_thread *quota_pick(struct evl_rq *rq)
+{
+	struct evl_thread *next, *curr = rq->curr;
+	struct evl_sched_quota *qs = &rq->quota;
+	struct evl_quota_group *tg;
+
 pick:
-	next = evl_get_schedq(&rq->fifo.runnable);
+	next = evl_get_schedq(&qs->runnable);
 	if (next == NULL) {
 		evl_stop_timer(&qs->limit_timer);
 		return NULL;
 	}
 
-	/*
-	 * As we basically piggyback on the SCHED_FIFO runqueue, make
-	 * sure to detect non-quota threads.
-	 */
 	tg = next->quota;
-	if (tg == NULL)
-		return next;
-
-	tg->run_start = now;
+	tg->nr_active--;
 
 	/*
 	 * Don't consider budget if kicked, we have to allow this
@@ -439,25 +438,22 @@ static struct evl_thread *quota_pick(struct evl_rq *rq)
 	 */
 	if (next->info & EVL_T_KICKED) {
 		evl_stop_timer(&qs->limit_timer);
-		goto out;
+		return next;
 	}
 
 	if (ktime_to_ns(tg->run_budget) == 0) {
-		/* Flush expired group members as we go. */
+		/* Park expired group members as we go. */
 		list_add_tail(&next->quota_expired, &tg->expired);
 		goto pick;
 	}
 
-	if (otg == tg && evl_timer_is_running(&qs->limit_timer))
-		/* Same group, leave the running timer untouched. */
-		goto out;
-
-	/* Arm limit timer for the new running group. */
-	evl_start_timer(&qs->limit_timer,
-			ktime_add(now, tg->run_budget),
-			EVL_INFINITE);
-out:
-	tg->nr_active--;
+	/* Arm new limit timer if need be. */
+	if (curr->quota != tg || !evl_timer_is_running(&qs->limit_timer)) {
+		tg->run_start = evl_ktime_monotonic();
+		evl_start_timer(&qs->limit_timer,
+				ktime_add(tg->run_start, tg->run_budget),
+				EVL_INFINITE);
+	}
 
 	return next;
 }
@@ -542,7 +538,7 @@ static int quota_destroy_group(struct evl_quota_group *tg,
 	 * Unregister the group before we drop rq->lock. As a result,
 	 * it won't accept threads anymore while we are busy moving
 	 * the current members to the fifo class, and concurrent
-	 * evl_quota_remove requests would receive -EINVAL.
+	 * quota_remove requests would receive -EINVAL.
 	 */
 	__clear_bit(tg->tgid, group_map);
 	list_del(&tg->next);
@@ -556,7 +552,7 @@ static int quota_destroy_group(struct evl_quota_group *tg,
 	 * hold rq->lock on entry, we do a trylock dance to prevent an
 	 * ABBA issue. No livelock is possible since we unregistered
 	 * that group already, so &tg->members can only be depleted
-	 * (by this loop specifically).
+	 * (by this loop exclusively).
 	 */
 
 	while (!list_empty(&tg->members)) {
@@ -583,10 +579,10 @@ static void quota_set_limit(struct evl_quota_group *tg,
 			int *quota_sum_r)
 {
 	struct evl_rq *rq = tg->rq;
-	struct evl_thread *thread, *tmp, *curr = rq->curr;
+	struct evl_thread *thread, *tmp;
 	struct evl_sched_quota *qs = &rq->quota;
-	ktime_t now, elapsed, consumed;
 	ktime_t old_quota = tg->quota;
+	ktime_t consumed;
 	u64 n;
 
 	assert_hard_lock(&rq->lock);
@@ -615,26 +611,18 @@ static void quota_set_limit(struct evl_quota_group *tg,
 	tg->quota_percent = quota_percent;
 	tg->quota_peak_percent = quota_peak_percent;
 
-	if (thread_on_quota(curr, tg)) {
-		now = evl_ktime_monotonic();
-
-		elapsed = now - tg->run_start;
-		if (elapsed < tg->run_budget)
-			tg->run_budget -= elapsed;
-		else
-			tg->run_budget = 0;
-
-		tg->run_start = now;
+	if (current_on_quota(tg)) {
+		quota_out(rq->curr);
 		evl_stop_timer(&qs->limit_timer);
 	}
 
 	if (tg->run_budget <= old_quota)
-		consumed = old_quota - tg->run_budget;
+		consumed = ktime_sub(old_quota, tg->run_budget);
 	else
 		consumed = 0;
 
 	if (tg->quota >= consumed)
-		tg->run_budget = tg->quota - consumed;
+		tg->run_budget = ktime_sub(tg->quota, consumed);
 	else
 		tg->run_budget = 0;
 
@@ -646,7 +634,7 @@ static void quota_set_limit(struct evl_quota_group *tg,
 		list_for_each_entry_safe_reverse(thread, tmp, &tg->expired,
 						quota_expired) {
 			list_del_init(&thread->quota_expired);
-			evl_add_schedq(&rq->fifo.runnable, thread);
+			evl_add_schedq(&qs->runnable, thread);
 		}
 	}
 
@@ -786,6 +774,7 @@ struct evl_sched_class evl_sched_quota = {
 	.sched_dequeue		=	quota_dequeue,
 	.sched_requeue		=	quota_requeue,
 	.sched_pick		=	quota_pick,
+	.sched_out		=	quota_out,
 	.sched_migrate		=	quota_migrate,
 	.sched_chkparam		=	quota_chkparam,
 	.sched_setparam		=	quota_setparam,
-- 
2.54.0