Re: [PATCH 1/2] sched/uclamp: Add a new sysctl to control RT default boost value

[Qais Yousef <qais.yousef@arm.com>]

On 04/20/20 10:29, Dietmar Eggemann wrote:
> On 03.04.20 14:30, Qais Yousef wrote:
> 
> [...]
> 
> > @@ -924,6 +945,14 @@ uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
> >  	return uc_req;
> >  }
> >  
> > +static void uclamp_rt_sync_default_util_min(struct task_struct *p)
> > +{
> > +	struct uclamp_se *uc_se = &p->uclamp_req[UCLAMP_MIN];
> > +
> > +	if (!uc_se->user_defined)
> > +		uclamp_se_set(uc_se, sysctl_sched_rt_default_uclamp_util_min, false);
> > +}
> > +
> >  unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
> >  {
> >  	struct uclamp_se uc_eff;
> > @@ -1030,6 +1059,12 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
> >  	if (unlikely(!p->sched_class->uclamp_enabled))
> >  		return;
> >  
> > +	/*
> > +	 * When sysctl_sched_rt_default_uclamp_util_min value is changed by the
> > +	 * user, we apply any new value on the next wakeup, which is here.
> > +	 */
> > +	uclamp_rt_sync_default_util_min(p);
> > +
> 
> Does this have to be an extra function? Can we not reuse
> uclamp_tg_restrict() by slightly rename it to uclamp_restrict()?

Hmm the thing is that we're not restricting here. In contrary we're boosting,
so the name would be misleading.

> 
> This function will then deal with enforcing restrictions, whether system
> and taskgroup hierarchy related or default value (latter only for rt-min
> right now since the others are fixed) related.
> 
> uclamp_eff_get() -> uclamp_restrict() is called from:
> 
>   'enqueue_task(), uclamp_update_active() -> uclamp_rq_inc() -> uclamp_rq_inc_id()' and
> 
>   'task_fits_capacity() -> clamp_task_util(), rt_task_fits_capacity() -> uclamp_eff_value()' and
> 
>   'schedutil_cpu_util(), find_energy_efficient_cpu() -> uclamp_rq_util_with() -> uclamp_eff_value()'
> 
> so there would be more check-points than the one in 'enqueue_task() -> uclamp_rq_inc()' now.

I think you're revolving around the same idea that Patrick was suggesting.
I think it is possible to do something in uclamp_eff_get() too.

Thanks

--
Qais Yousef

> 
> Only lightly tested:
> 
> ---8<---
> 
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Date: Sun, 19 Apr 2020 01:20:17 +0200
> Subject: [PATCH] sched/core: uclamp: Move uclamp_rt_sync_default_util_min()
>  into uclamp_tg_restrict()
> 
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> ---
>  kernel/sched/core.c | 34 +++++++++++++++-------------------
>  1 file changed, 15 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 8f4e0d5c7daf..6802113d6d4b 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -899,12 +899,22 @@ unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
>  }
>  
>  static inline struct uclamp_se
> -uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
> +uclamp_restrict(struct task_struct *p, enum uclamp_id clamp_id)
>  {
> -	struct uclamp_se uc_req = p->uclamp_req[clamp_id];
> -#ifdef CONFIG_UCLAMP_TASK_GROUP
> -	struct uclamp_se uc_max;
> +	struct uclamp_se uc_req, __maybe_unused uc_max;
> +
> +	if (unlikely(rt_task(p)) && clamp_id == UCLAMP_MIN &&
> +	    !uc_req.user_defined) {
> +		struct uclamp_se *uc_se = &p->uclamp_req[UCLAMP_MIN];
> +		int rt_min = sysctl_sched_rt_default_uclamp_util_min;
> +
> +		if (uc_se->value != rt_min)
> +			uclamp_se_set(uc_se, rt_min, false);
> +	}
>  
> +	uc_req = p->uclamp_req[clamp_id];
> +
> +#ifdef CONFIG_UCLAMP_TASK_GROUP
>  	/*
>  	 * Tasks in autogroups or root task group will be
>  	 * restricted by system defaults.
> @@ -933,7 +943,7 @@ uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
>  static inline struct uclamp_se
>  uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
>  {
> -	struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
> +	struct uclamp_se uc_req = uclamp_restrict(p, clamp_id);
>  	struct uclamp_se uc_max = uclamp_default[clamp_id];
>  
>  	/* System default restrictions always apply */
> @@ -943,14 +953,6 @@ uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
>  	return uc_req;
>  }
>  
> -static void uclamp_rt_sync_default_util_min(struct task_struct *p)
> -{
> -	struct uclamp_se *uc_se = &p->uclamp_req[UCLAMP_MIN];
> -
> -	if (!uc_se->user_defined)
> -		uclamp_se_set(uc_se, sysctl_sched_rt_default_uclamp_util_min, false);
> -}
> -
>  unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
>  {
>  	struct uclamp_se uc_eff;
> @@ -1057,12 +1059,6 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
>  	if (unlikely(!p->sched_class->uclamp_enabled))
>  		return;
>  
> -	/*
> -	 * When sysctl_sched_rt_default_uclamp_util_min value is changed by the
> -	 * user, we apply any new value on the next wakeup, which is here.
> -	 */
> -	uclamp_rt_sync_default_util_min(p);
> -
>  	for_each_clamp_id(clamp_id)
>  		uclamp_rq_inc_id(rq, p, clamp_id);
>  
> -- 
> 2.17.1