linux-kernel - Re: [PATCH v7 03/15] sched/core: uclamp: Add system default clamps

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Date:   Wed, 13 Mar 2019 21:13:42 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-api@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        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>
Subject: Re: [PATCH v7 03/15] sched/core: uclamp: Add system default clamps

On Fri, Feb 08, 2019 at 10:05:42AM +0000, Patrick Bellasi wrote:
> +int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
> +				void __user *buffer, size_t *lenp,
> +				loff_t *ppos)
> +{
> +	int old_min, old_max;
> +	int result = 0;

Should this not have an internal mutex to serialize concurrent usage?
See for example sched_rt_handler().

> +
> +	old_min = sysctl_sched_uclamp_util_min;
> +	old_max = sysctl_sched_uclamp_util_max;
> +
> +	result = proc_dointvec(table, write, buffer, lenp, ppos);
> +	if (result)
> +		goto undo;
> +	if (!write)
> +		goto done;
> +
> +	if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
> +	    sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE) {
> +		result = -EINVAL;
> +		goto undo;
> +	}
> +
> +	if (old_min != sysctl_sched_uclamp_util_min) {
> +		uclamp_default[UCLAMP_MIN].value =
> +			sysctl_sched_uclamp_util_min;
> +		uclamp_default[UCLAMP_MIN].bucket_id =
> +			uclamp_bucket_id(sysctl_sched_uclamp_util_min);
> +	}
> +	if (old_max != sysctl_sched_uclamp_util_max) {
> +		uclamp_default[UCLAMP_MAX].value =
> +			sysctl_sched_uclamp_util_max;
> +		uclamp_default[UCLAMP_MAX].bucket_id =
> +			uclamp_bucket_id(sysctl_sched_uclamp_util_max);
> +	}
> +
> +	/*
> +	 * Updating all the RUNNABLE task is expensive, keep it simple and do
> +	 * just a lazy update at each next enqueue time.
> +	 */
> +	goto done;
> +
> +undo:
> +	sysctl_sched_uclamp_util_min = old_min;
> +	sysctl_sched_uclamp_util_max = old_max;
> +done:
> +
> +	return result;
> +}