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SubjectRe: [PATCH 1/1] sched/uclamp: release per-task uclamp control if user set to default value
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Hi Yun,

On 28/09/2020 10:26, Yun Hsiang wrote:
> If the user wants to release the util clamp and let cgroup to control it,
> we need a method to reset.
>
> So if the user set the task uclamp to the default value (0 for UCLAMP_MIN
> and 1024 for UCLAMP_MAX), reset the user_defined flag to release control.
>
> Signed-off-by: Yun Hsiang <hsiang023167@gmail.com>

could you explain with a little bit more detail why you would need this
feature?

Currently we assume that once the per-task uclamp (user-defined) values
are set, you could only change the effective uclamp values of this task
by (1) moving it into another taskgroup or (2) changing the system
default uclamp values.

> ---
> kernel/sched/core.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9a2fbf98fd6f..fa63d70d783a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1187,6 +1187,7 @@ static void __setscheduler_uclamp(struct task_struct *p,
> const struct sched_attr *attr)
> {
> enum uclamp_id clamp_id;
> + bool user_defined;
>
> /*
> * On scheduling class change, reset to default clamps for tasks
> @@ -1210,14 +1211,16 @@ static void __setscheduler_uclamp(struct task_struct *p,
> if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
> return;
>
> + user_defined = attr->sched_util_min == 0 ? false : true;
> if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
> uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
> - attr->sched_util_min, true);
> + attr->sched_util_min, user_defined);
> }
>
> + user_defined = attr->sched_util_max == 1024 ? false : true;
> if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
> uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
> - attr->sched_util_max, true);
> + attr->sched_util_max, user_defined);
> }
> }

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