Re: [PATCH v7 02/15] sched/core: uclamp: Enforce last task UCLAMP_MAX

From: Peter Zijlstra <peterz@infradead.org>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	linux-api@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Tejun Heo <tj@kernel.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Paul Turner <pjt@google.com>,
	Quentin Perret <quentin.perret@arm.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
	Joel Fernandes <joelaf@google.com>,
	Steve Muckle <smuckle@google.com>,
	Suren Baghdasaryan <surenb@google.com>
Subject: Re: [PATCH v7 02/15] sched/core: uclamp: Enforce last task UCLAMP_MAX
Date: Wed, 13 Mar 2019 15:12:53 +0100	[thread overview]
Message-ID: <20190313141253.GG5922@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190208100554.32196-3-patrick.bellasi@arm.com>

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;
> +}