linux-kernel - Re: [PATCH v2 1/4] sched/uclamp: Make uclamp_util

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Date:   Wed, 4 Dec 2019 16:22:44 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Quentin Perret <qperret@...gle.com>,
        Qais Yousef <qais.yousef@....com>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v2 1/4] sched/uclamp: Make uclamp_util_*() helpers use and
 return UL values

On Tue, 3 Dec 2019 at 17:02, Valentin Schneider
<valentin.schneider@....com> wrote:
>
> Vincent pointed out recently that the canonical type for utilization
> values is 'unsigned long'. Internally uclamp uses 'unsigned int' values for
> cache optimization, but this doesn't have to be exported to its users.
>
> Make the uclamp helpers that deal with utilization use and return unsigned
> long values.
>
> Reviewed-by: Quentin Perret <qperret@...gle.com>
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> ---
>  kernel/sched/sched.h | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 280a3c735935..f1d035e5df7e 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2303,15 +2303,15 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
>  unsigned int uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);

Why not changing uclamp_eff_value to return unsigned long too ? The
returned value represents a utilization to be compared with other
utilization value

>
>  static __always_inline
> -unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
> -                             struct task_struct *p)
> +unsigned long uclamp_util_with(struct rq *rq, unsigned long util,
> +                              struct task_struct *p)
>  {
> -       unsigned int min_util = READ_ONCE(rq->uclamp[UCLAMP_MIN].value);
> -       unsigned int max_util = READ_ONCE(rq->uclamp[UCLAMP_MAX].value);
> +       unsigned long min_util = READ_ONCE(rq->uclamp[UCLAMP_MIN].value);
> +       unsigned long max_util = READ_ONCE(rq->uclamp[UCLAMP_MAX].value);
>
>         if (p) {
> -               min_util = max(min_util, uclamp_eff_value(p, UCLAMP_MIN));
> -               max_util = max(max_util, uclamp_eff_value(p, UCLAMP_MAX));
> +               min_util = max_t(unsigned long, min_util, uclamp_eff_value(p, UCLAMP_MIN));

As mentioned above, uclamp_eff_value should return an unsigned long

> +               max_util = max_t(unsigned long, max_util, uclamp_eff_value(p, UCLAMP_MAX));
>         }
>
>         /*
> @@ -2325,17 +2325,17 @@ unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
>         return clamp(util, min_util, max_util);
>  }
>
> -static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
> +static inline unsigned long uclamp_util(struct rq *rq, unsigned long util)
>  {
>         return uclamp_util_with(rq, util, NULL);
>  }
>  #else /* CONFIG_UCLAMP_TASK */
> -static inline unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
> -                                           struct task_struct *p)
> +static inline unsigned long uclamp_util_with(struct rq *rq, unsigned long util,
> +                                            struct task_struct *p)
>  {
>         return util;
>  }
> -static inline unsigned int uclamp_util(struct rq *rq, unsigned int util)
> +static inline unsigned long uclamp_util(struct rq *rq, unsigned long util)
>  {
>         return util;
>  }
> --
> 2.24.0
>