On 25/10/2020 08:36, Yun Hsiang wrote:
> If the user wants to stop controlling uclamp and let the task inherit
> the value from the group, we need a method to reset.
>
> Add SCHED_FLAG_UTIL_CLAMP_RESET flag to allow the user to reset uclamp via
> sched_setattr syscall.
>
> The policy is
> _CLAMP_RESET => reset both min and max
> _CLAMP_RESET | _CLAMP_MIN => reset min value
> _CLAMP_RESET | _CLAMP_MAX => reset max value
> _CLAMP_RESET | _CLAMP_MIN | _CLAMP_MAX => reset both min and max
>
> Signed-off-by: Yun Hsiang <hsiang023...@gmail.com>
[...]
> @@ -1451,7 +1464,8 @@ static void __setscheduler_uclamp(struct task_struct *p,
> struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
>
> /* Keep using defined clamps across class changes */
> - if (uc_se->user_defined)
> + if (flags != SCHED_FLAG_UTIL_CLAMP_RESET &&
> + uc_se->user_defined)
> continue;
With:
(1) _CLAMP_RESET => reset both min and max
(2) _CLAMP_RESET | _CLAMP_MIN => reset min value
(3) _CLAMP_RESET | _CLAMP_MAX => reset max value
(4) _CLAMP_RESET | _CLAMP_MIN | _CLAMP_MAX => reset both min and max
If you reset an RT task with (1) you don't reset its uclamp.min value.
__uclamp_update_util_min_rt_default(p) doesn't know about
SCHED_FLAG_UTIL_CLAMP_RESET. It only knows user_defined and will bail early.
[...]
> - if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
> + if (likely(!flags || flags == SCHED_FLAG_UTIL_CLAMP_RESET))
> return;
>
> - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
> + if (flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
> + if (reset) {
> + clamp_value = __default_uclamp_value(p, UCLAMP_MIN);
> + user_defined = false;
> + } else {
> + clamp_value = attr->sched_util_min;
> + user_defined = true;
> + }
Why do you reset for (1) in the for_each_clamp_id(clamp_id) loop and for
(2)-(4) in the if (flags & SCHED_FLAG_UTIL_CLAMP_MXX) condition?
You could reset (1)-(4) in the for_each_clamp_id(clamp_id) loop? In this
case you wouldn't need __default_uclamp_value().
[...]
