linux-kernel - Re: [PATCH v7 02/15] sched/core: uclamp: Enforce last task UCLAMP

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Message-ID: <20190313141253.GG5922@hirez.programming.kicks-ass.net>
Date:   Wed, 13 Mar 2019 15:12:53 +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 02/15] sched/core: uclamp: Enforce last task UCLAMP_MAX

On Fri, Feb 08, 2019 at 10:05:41AM +0000, Patrick Bellasi wrote:
> +static inline void uclamp_idle_reset(struct rq *rq, unsigned int clamp_id,
> +				     unsigned int clamp_value)
> +{
> +	/* Reset max-clamp retention only on idle exit */
> +	if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
> +		return;
> +
> +	WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
> +
> +	/*
> +	 * This function is called for both UCLAMP_MIN (before) and UCLAMP_MAX
> +	 * (after). The idle flag is reset only the second time, when we know
> +	 * that UCLAMP_MIN has been already updated.

Why do we care? That is, what is this comment trying to tell us.

> +	 */
> +	if (clamp_id == UCLAMP_MAX)
> +		rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
> +}