linux-kernel - Re: [PATCH] sched/uclamp: Fix overzealous type replacement

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Message-ID: <CAKfTPtCeGPS57wdyVjA7mnQTW4EeTrd0LX-_1f_+MWp--1FRNQ@mail.gmail.com>
Date:   Fri, 15 Nov 2019 09:12:58 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dietmar Eggemann <Dietmar.Eggemann@....com>,
        Tejun Heo <tj@...nel.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH] sched/uclamp: Fix overzealous type replacement

On Wed, 13 Nov 2019 at 17:55, Valentin Schneider
<valentin.schneider@....com> wrote:
>
> Some uclamp helpers had their return type changed from 'unsigned int' to
> 'enum uclamp_id' by commit
>
>   0413d7f33e60 ("sched/uclamp: Always use 'enum uclamp_id' for clamp_id values")
>
> but it happens that some *actually* do return an unsigned int value. Those
> are the helpers that return a utilization value: uclamp_rq_max_value() and
> uclamp_eff_value(). Fix those up.
>
> Note that this doesn't lead to any obj diff using a relatively recent
> aarch64 compiler (8.3-2019.03). The current code of e.g. uclamp_eff_value()
> already figures out that the return value is 11 bits (bits_per(1024)) and
> doesn't seem to do anything funny. I'm still marking this as fixing the
> above commit to be on the safe side.
>
> Fixes: 0413d7f33e60 ("sched/uclamp: Always use 'enum uclamp_id' for clamp_id values")
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>
> ---
>  kernel/sched/core.c  | 4 ++--
>  kernel/sched/sched.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 513a4794ff36..71a45025cd2e 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -853,7 +853,7 @@ static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
>  }
>
>  static inline
> -enum uclamp_id uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
> +unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
>                                    unsigned int clamp_value)
>  {
>         struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
> @@ -918,7 +918,7 @@ uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
>         return uc_req;
>  }
>
> -enum uclamp_id uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
> +unsigned int uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
>  {
>         struct uclamp_se uc_eff;
>

And static inline enum uclamp_id uclamp_none(enum uclamp_id clamp_id) ?

Should it be fixed as well as it can return SCHED_CAPACITY_SCALE ?



> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 05c282775f21..280a3c735935 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2300,7 +2300,7 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
>  #endif /* CONFIG_CPU_FREQ */
>
>  #ifdef CONFIG_UCLAMP_TASK
> -enum uclamp_id uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
> +unsigned int uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
>
>  static __always_inline
>  unsigned int uclamp_util_with(struct rq *rq, unsigned int util,
> --
> 2.22.0
>