linux-kernel - Re: [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps

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Date:   Tue, 6 Aug 2019 18:11:53 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-api@...r.kernel.org, cgroups@...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>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....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>,
        Alessio Balsini <balsini@...roid.com>
Subject: Re: [PATCH v13 2/6] sched/core: uclamp: Propagate parent clamps

On Fri, Aug 02, 2019 at 10:08:49AM +0100, Patrick Bellasi <patrick.bellasi@....com> wrote:
> @@ -7095,6 +7149,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>  	if (req.ret)
>  		return req.ret;
>  
> +	mutex_lock(&uclamp_mutex);
>  	rcu_read_lock();
>  
>  	tg = css_tg(of_css(of));
> @@ -7107,7 +7162,11 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
>  	 */
>  	tg->uclamp_pct[clamp_id] = req.percent;
>  
> +	/* Update effective clamps to track the most restrictive value */
> +	cpu_util_update_eff(of_css(of));
> +
>  	rcu_read_unlock();
> +	mutex_unlock(&uclamp_mutex);
Following my remarks to "[PATCH v13 1/6] sched/core: uclamp: Extend
CPU's cgroup", I wonder if the rcu_read_lock() couldn't be moved right
before cpu_util_update_eff(). And by extension rcu_read_(un)lock could
be hidden into cpu_util_update_eff() closer to its actual need.


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