Re: [PATCH v5 1/1] sched/uclamp: add SCHED_FLAG_UTIL_CLAMP_RESET flag to reset uclamp

[Peter Zijlstra]

On Wed, Nov 11, 2020 at 06:41:07PM +0100, Dietmar Eggemann wrote:
> diff --git a/include/uapi/linux/sched/types.h 
> b/include/uapi/linux/sched/types.h
> index c852153ddb0d..b9165f17dddc 100644
> --- a/include/uapi/linux/sched/types.h
> +++ b/include/uapi/linux/sched/types.h
> @@ -115,8 +115,8 @@ struct sched_attr {
>       __u64 sched_period;
>  
>       /* Utilization hints */
> -     __u32 sched_util_min;
> -     __u32 sched_util_max;
> +     __s32 sched_util_min;
> +     __s32 sched_util_max;

So that's UAPI, not sure we can change the type here.

>  };
>  
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3dc415f58bd7..caaa2a8434b9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1413,17 +1413,24 @@ int sysctl_sched_uclamp_handler(struct ctl_table 
> *table, int write,
>  static int uclamp_validate(struct task_struct *p,
>                          const struct sched_attr *attr)
>  {
> -     unsigned int lower_bound = p->uclamp_req[UCLAMP_MIN].value;
> -     unsigned int upper_bound = p->uclamp_req[UCLAMP_MAX].value;
> +     int util_min = p->uclamp_req[UCLAMP_MIN].value;
> +     int util_max = p->uclamp_req[UCLAMP_MAX].value;
>  
> -     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN)
> -             lower_bound = attr->sched_util_min;
> -     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX)
> -             upper_bound = attr->sched_util_max;
> +     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
> +             util_min = attr->sched_util_min;
>  
> -     if (lower_bound > upper_bound)
> -             return -EINVAL;
> -     if (upper_bound > SCHED_CAPACITY_SCALE)
> +             if (util_min < -1 || util_min > SCHED_CAPACITY_SCALE)
> +                     return -EINVAL;
> +     }
> +
> +     if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
> +             util_max = attr->sched_util_max;
> +
> +             if (util_max < -1 || util_max > SCHED_CAPACITY_SCALE)
> +                     return -EINVAL;
> +     }

Luckily we can write that range as a single branch like:

        if (util_{min,max} + 1 > SCHED_CAPACITY_SCALE+1)

which assumes u32 :-)

> +
> +     if (util_min != -1 && util_max != -1 && util_min > util_max)
>               return -EINVAL;

I think that will compile as is, otherwise write it like ~0u, which is
the same bit pattern.