Re: [PATCH 7/7] sched/uclamp: Cater for uclamp in find_energy_efficient_cpu()'s early exit condition

[Xuewen Yan <xuewen.yan94@gmail.com>]

Hi Qais

On Thu, Jun 30, 2022 at 3:48 AM Qais Yousef <qais.yousef@arm.com> wrote:
>
> If the utilization of the woken up task is 0, we skip the energy
> calculation because it has no impact.
>
> But if the task is boosted (uclamp_min != 0) will have an impact on task
> placement and frequency selection. Only skip if the util is truly
> 0 after applying uclamp values.
>
> Change uclamp_task_cpu() signature to avoid unnecessary additional calls
> to uclamp_eff_get(). feec() is the only user now.
>
> Fixes: 732cd75b8c920 ("sched/fair: Select an energy-efficient CPU on task wake-up")
> Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> ---
>  kernel/sched/fair.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 499ef7a7288c..a112ca45864c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4057,14 +4057,16 @@ static inline unsigned long task_util_est(struct task_struct *p)
>  }
>
>  #ifdef CONFIG_UCLAMP_TASK
> -static inline unsigned long uclamp_task_util(struct task_struct *p)
> +static inline unsigned long uclamp_task_util(struct task_struct *p,
> +                                            unsigned long uclamp_min,
> +                                            unsigned long uclamp_max)
>  {
> -       return clamp(task_util_est(p),
> -                    uclamp_eff_value(p, UCLAMP_MIN),
> -                    uclamp_eff_value(p, UCLAMP_MAX));
> +       return clamp(task_util_est(p), uclamp_min, uclamp_max);
>  }
>  #else
> -static inline unsigned long uclamp_task_util(struct task_struct *p)
> +static inline unsigned long uclamp_task_util(struct task_struct *p,
> +                                            unsigned long uclamp_min,
> +                                            unsigned long uclamp_max)
>  {
>         return task_util_est(p);
>  }
> @@ -6913,7 +6915,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
>         target = prev_cpu;
>
>         sync_entity_load_avg(&p->se);
> -       if (!task_util_est(p))
> +       if (!uclamp_task_util(p, p_util_min, p_util_max))

Is it not enough to just replace the task_util_est with the
uclamp_task_util? If change the definition of uclamp_task_util,
that means it have to get task's uclamp first if user want to call the
function, may increase the code complex farther more?

>                 goto unlock;
>
>         for (; pd; pd = pd->next) {
> --
> 2.25.1
>

BR
---
xuewen.yan