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

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Date:   Wed, 15 Aug 2018 17:02:42 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Patrick Bellasi <patrick.bellasi@....com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     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 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.

[...]