[PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[Xunlei Pang]

Two minor fixes for cfs_rq_clock_task().
1) If cfs_rq is currently being throttled, we need to subtract the cfs
   throttled clock time.

2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
   need it as well.

Signed-off-by: Xunlei Pang <xlpang@redhat.com>
---
 kernel/sched/fair.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1708729e..fb80a12 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
 static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
 {
 	if (unlikely(cfs_rq->throttle_count))
-		return cfs_rq->throttled_clock_task;
+		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
 
 	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
 }
@@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
 	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
 
 	cfs_rq->throttle_count--;
-#ifdef CONFIG_SMP
 	if (!cfs_rq->throttle_count) {
 		/* adjust cfs_rq_clock_task() */
 		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
 					     cfs_rq->throttled_clock_task;
 	}
-#endif
 
 	return 0;
 }
-- 
1.8.3.1

Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[bsegall]

Xunlei Pang <xlpang@redhat.com> writes:

> Two minor fixes for cfs_rq_clock_task().
> 1) If cfs_rq is currently being throttled, we need to subtract the cfs
>    throttled clock time.
>
> 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
>    need it as well.
>
> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
> ---
>  kernel/sched/fair.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1708729e..fb80a12 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
>  static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
>  {
>  	if (unlikely(cfs_rq->throttle_count))
> -		return cfs_rq->throttled_clock_task;
> +		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
>  
>  	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
>  }
> @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
>  	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
>  
>  	cfs_rq->throttle_count--;
> -#ifdef CONFIG_SMP
>  	if (!cfs_rq->throttle_count) {
>  		/* adjust cfs_rq_clock_task() */
>  		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
>  					     cfs_rq->throttled_clock_task;
>  	}
> -#endif
>  
>  	return 0;
>  }

[Cc: pjt@google.com]

This looks reasonable to me (at least the first part; I'm not
certain why the CONFIG_SMP ifdef was put in place).

Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[Peter Zijlstra]

On Tue, May 10, 2016 at 11:19:44AM -0700, bsegall@google.com wrote:
> Xunlei Pang <xlpang@redhat.com> writes:
> 
> > Two minor fixes for cfs_rq_clock_task().
> > 1) If cfs_rq is currently being throttled, we need to subtract the cfs
> >    throttled clock time.
> >
> > 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
> >    need it as well.
> >
> > Signed-off-by: Xunlei Pang <xlpang@redhat.com>
> > ---
> >  kernel/sched/fair.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1708729e..fb80a12 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
> >  static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
> >  {
> >  	if (unlikely(cfs_rq->throttle_count))
> > -		return cfs_rq->throttled_clock_task;
> > +		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
> >  
> >  	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
> >  }

The alternative is obviously to do the subtraction in
tg_throttle_down(), were we set ->throttled_clock_task.

> > @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
> >  	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
> >  
> >  	cfs_rq->throttle_count--;
> > -#ifdef CONFIG_SMP
> >  	if (!cfs_rq->throttle_count) {
> >  		/* adjust cfs_rq_clock_task() */
> >  		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
> >  					     cfs_rq->throttled_clock_task;
> >  	}
> > -#endif
> >  
> >  	return 0;
> >  }
> 
> [Cc: pjt@google.com]
> 
> This looks reasonable to me (at least the first part; I'm not
> certain why the CONFIG_SMP ifdef was put in place).

64660c864f46 ("sched: Prevent interactions with throttled entities")

Introduced it, because at that time it was about updating shares, which
is only present on SMP. Then:

f1b17280efbd ("sched: Maintain runnable averages across throttled periods")

Added the clock thing inside it, and:

82958366cfea ("sched: Replace update_shares weight distribution with per-entity computation")

took out the shares update and left the clock update, resulting in the
current code.

Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[Xunlei Pang]

On 2016/05/11 at 14:49, Peter Zijlstra wrote:
> On Tue, May 10, 2016 at 11:19:44AM -0700, bsegall@google.com wrote:
>> Xunlei Pang <xlpang@redhat.com> writes:
>>
>>> Two minor fixes for cfs_rq_clock_task().
>>> 1) If cfs_rq is currently being throttled, we need to subtract the cfs
>>>    throttled clock time.
>>>
>>> 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
>>>    need it as well.
>>>
>>> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
>>> ---
>>>  kernel/sched/fair.c | 4 +---
>>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index 1708729e..fb80a12 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
>>>  static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
>>>  {
>>>  	if (unlikely(cfs_rq->throttle_count))
>>> -		return cfs_rq->throttled_clock_task;
>>> +		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
>>>  
>>>  	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
>>>  }
> The alternative is obviously to do the subtraction in
> tg_throttle_down(), were we set ->throttled_clock_task.

It is possible, but throttled_clock_task is a timestamp, I think doing it here is semantically better.

>
>>> @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
>>>  	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
>>>  
>>>  	cfs_rq->throttle_count--;
>>> -#ifdef CONFIG_SMP
>>>  	if (!cfs_rq->throttle_count) {
>>>  		/* adjust cfs_rq_clock_task() */
>>>  		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
>>>  					     cfs_rq->throttled_clock_task;
>>>  	}
>>> -#endif
>>>  
>>>  	return 0;
>>>  }
>> [Cc: pjt@google.com]
>>
>> This looks reasonable to me (at least the first part; I'm not
>> certain why the CONFIG_SMP ifdef was put in place).
> 64660c864f46 ("sched: Prevent interactions with throttled entities")
>
> Introduced it, because at that time it was about updating shares, which
> is only present on SMP. Then:
>
> f1b17280efbd ("sched: Maintain runnable averages across throttled periods")
>
> Added the clock thing inside it, and:
>
> 82958366cfea ("sched: Replace update_shares weight distribution with per-entity computation")
>
> took out the shares update and left the clock update, resulting in the
> current code.
>
>

Thanks,
Xunlei

Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[Xunlei Pang]

Ping

On 2016/05/12 at 11:36, Xunlei Pang wrote:
> On 2016/05/11 at 14:49, Peter Zijlstra wrote:
>> On Tue, May 10, 2016 at 11:19:44AM -0700, bsegall@google.com wrote:
>>> Xunlei Pang <xlpang@redhat.com> writes:
>>>
>>>> Two minor fixes for cfs_rq_clock_task().
>>>> 1) If cfs_rq is currently being throttled, we need to subtract the cfs
>>>>    throttled clock time.
>>>>
>>>> 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
>>>>    need it as well.
>>>>
>>>> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
>>>> ---
>>>>  kernel/sched/fair.c | 4 +---
>>>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>>>
>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>> index 1708729e..fb80a12 100644
>>>> --- a/kernel/sched/fair.c
>>>> +++ b/kernel/sched/fair.c
>>>> @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
>>>>  static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
>>>>  {
>>>>  	if (unlikely(cfs_rq->throttle_count))
>>>> -		return cfs_rq->throttled_clock_task;
>>>> +		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
>>>>  
>>>>  	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
>>>>  }
>> The alternative is obviously to do the subtraction in
>> tg_throttle_down(), were we set ->throttled_clock_task.
> It is possible, but throttled_clock_task is a timestamp, I think doing it here is semantically better.
>
>>>> @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
>>>>  	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
>>>>  
>>>>  	cfs_rq->throttle_count--;
>>>> -#ifdef CONFIG_SMP
>>>>  	if (!cfs_rq->throttle_count) {
>>>>  		/* adjust cfs_rq_clock_task() */
>>>>  		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
>>>>  					     cfs_rq->throttled_clock_task;
>>>>  	}
>>>> -#endif
>>>>  
>>>>  	return 0;
>>>>  }
>>> [Cc: pjt@google.com]
>>>
>>> This looks reasonable to me (at least the first part; I'm not
>>> certain why the CONFIG_SMP ifdef was put in place).
>> 64660c864f46 ("sched: Prevent interactions with throttled entities")
>>
>> Introduced it, because at that time it was about updating shares, which
>> is only present on SMP. Then:
>>
>> f1b17280efbd ("sched: Maintain runnable averages across throttled periods")
>>
>> Added the clock thing inside it, and:
>>
>> 82958366cfea ("sched: Replace update_shares weight distribution with per-entity computation")
>>
>> took out the shares update and left the clock update, resulting in the
>> current code.
>>
>>
> Thanks,
> Xunlei
>

[tip:sched/core] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

[tip-bot for Xunlei Pang]

Commit-ID:  1a99ae3f00d3c7c7885ee529ac9a874b19caa0cf
Gitweb:     http://git.kernel.org/tip/1a99ae3f00d3c7c7885ee529ac9a874b19caa0cf
Author:     Xunlei Pang <xlpang@redhat.com>
AuthorDate: Tue, 10 May 2016 21:03:18 +0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 3 Jun 2016 09:18:56 +0200

sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

Two minor fixes for cfs_rq_clock_task():

 1) If cfs_rq is currently being throttled, we need to subtract the cfs
    throttled clock time.

 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
    need it as well.

Signed-off-by: Xunlei Pang <xlpang@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1462885398-14724-1-git-send-email-xlpang@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/fair.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 218f8e8..1e87bb6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3688,7 +3688,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
 static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
 {
 	if (unlikely(cfs_rq->throttle_count))
-		return cfs_rq->throttled_clock_task;
+		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
 
 	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
 }
@@ -3826,13 +3826,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
 	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
 
 	cfs_rq->throttle_count--;
-#ifdef CONFIG_SMP
 	if (!cfs_rq->throttle_count) {
 		/* adjust cfs_rq_clock_task() */
 		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
 					     cfs_rq->throttled_clock_task;
 	}
-#endif
 
 	return 0;
 }