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, bseg...@google.com wrote:
>>> Xunlei Pang  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 
 ---
  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: p...@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]

On 2016/05/11 at 14:49, Peter Zijlstra wrote:
> On Tue, May 10, 2016 at 11:19:44AM -0700, bseg...@google.com wrote:
>> Xunlei Pang  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 
>>> ---
>>>  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: p...@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()

[Peter Zijlstra]

On Tue, May 10, 2016 at 11:19:44AM -0700, bseg...@google.com wrote:
> Xunlei Pang  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 
> > ---
> >  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: p...@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()

[bsegall]

Xunlei Pang  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 
> ---
>  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: p...@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).

[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 
---
 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