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

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Message-ID: <20180816132249.GA2960@e110439-lin>
Date:   Thu, 16 Aug 2018 14:22:49 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v3 04/14] sched/core: uclamp: update CPU's refcount on
 clamp changes

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