Re: [PATCH v2] sched/uclamp: Fix overzealous type replacement

[Vincent Guittot]

On Fri, 15 Nov 2019 at 11:39, Valentin Schneider
<valentin.schneider@xxxxxxx> 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 do return a value in the [0, SCHED_CAPACITY_SCALE]
> range, which should really be unsigned int. The affected helpers are
> uclamp_none(), 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()
> properly returns an 11 bit value (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")
> Reviewed-by: Qais Yousef <qais.yousef@xxxxxxx>
> Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
> ---
> v2 changes:
> o Also fix uclamp_none() (Vincent)
> o Collect reviewed-by
> o Slightly reword changelog
> ---
>  kernel/sched/core.c  | 6 +++---
>  kernel/sched/sched.h | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 513a4794ff36..3ceff1c93ef1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -810,7 +810,7 @@ static inline unsigned int uclamp_bucket_base_value(unsigned int clamp_value)
>         return UCLAMP_BUCKET_DELTA * uclamp_bucket_id(clamp_value);
>  }
>
> -static inline enum uclamp_id uclamp_none(enum uclamp_id clamp_id)
> +static inline unsigned int uclamp_none(enum uclamp_id clamp_id)

Out of curiosity why uclamp decided to use unsigned int to manipulate
utilization instead of unsigned long which is the type of util_avg ?

>  {
>         if (clamp_id == UCLAMP_MIN)
>                 return 0;
> @@ -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;
>
> 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
>