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

Peter Zijlstra
2020-11-11T18:05:10Z

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.