Re: [PATCH v3 04/14] sched/core: uclamp: update CPU's refcount on clamp changes

Patrick Bellasi
2018-08-16T13:22:49Z

On 15-Aug 17:02, Dietmar Eggemann wrote:
> On 08/06/2018 06:39 PM, Patrick Bellasi wrote:
>
> [...]
>
> >+/**
> >+ * uclamp_task_active: check if a task is currently clamping a CPU
> >+ * @p: the task to check
> >+ *
> >+ * A task actively affects the utilization clamp of a CPU if:
> >+ * - it's currently enqueued or running on that CPU
> >+ * - it's refcounted in at least one clamp group of that CPU
> >+ *
> >+ * Return: true if p is currently clamping the utilization of its CPU.
> >+ */
> >+static inline bool uclamp_task_active(struct task_struct *p)
> >+{
> >+ struct rq *rq = task_rq(p);
> >+ int clamp_id;
> >+
> >+ lockdep_assert_held(&p->pi_lock);
> >+ lockdep_assert_held(&rq->lock);
> >+
> >+ if (!task_on_rq_queued(p) && !p->on_cpu)
> >+ return false;
> >+
> >+ for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
> >+ if (uclamp_task_affects(p, clamp_id))
> >+ return true;
> >+ }
> >+
> >+ return false;
> >+}
>
> Looks like that uclamp_task_active() is only used once (in
> uclamp_task_update_active()). Can you not code the if condition and the for
> loop directly in uclamp_task_update_active()? This would save code
> (lockdep_assert_held() etc.) and comment lines.

Yes, that's possible... and we will have:

---8<---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ae528a7b9bef..0c8bec892018 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1331,7 +1331,9 @@ uclamp_task_update_active(struct task_struct *p, int clamp_id, int group_id)
* index, then that task is not yet RUNNABLE and it's going to be
* enqueued with the proper clamp group value.
*/
- if (!uclamp_task_active(p))
+ if (!task_on_rq_queued(p) && !p->on_cpu)
+ goto done;
+ if (!uclamp_task_affects(p, clamp_id))
goto done;

/* Release p's currently referenced clamp group */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 11d139faed1f..65fdf4abc6ff 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2231,35 +2231,6 @@ static inline bool uclamp_task_affects(struct task_struct *p, int clamp_id)
{
return (p->uclamp[clamp_id].effective.group_id != UCLAMP_NOT_VALID);
}
-
-/**
- * uclamp_task_active: check if a task is currently clamping a CPU
- * @p: the task to check
- *
- * A task actively affects the utilization clamp of a CPU if:
- * - it's currently enqueued or running on that CPU
- * - it's refcounted in at least one clamp group of that CPU
- *
- * Return: true if p is currently clamping the utilization of its CPU.
- */
-static inline bool uclamp_task_active(struct task_struct *p)
-{
- struct rq *rq = task_rq(p);
- int clamp_id;
-
- lockdep_assert_held(&p->pi_lock);
- lockdep_assert_held(&rq->lock);
-
- if (!task_on_rq_queued(p) && !p->on_cpu)
- return false;
-
- for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id) {
- if (uclamp_task_affects(p, clamp_id))
- return true;
- }
-
- return false;
-}
#endif /* CONFIG_UCLAMP_TASK */

#ifdef CONFIG_CPU_FREQ
---8<---

I'll add this to the next posting!

Cheers Patrick

--
#include <best/regards.h>

Patrick Bellasi