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

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Message-ID: <20190314170619.rt6yhelj3y6dzypu@e110439-lin>
Date:   Thu, 14 Mar 2019 17:06:19 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <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>
Subject: Re: [PATCH v7 02/15] sched/core: uclamp: Enforce last task UCLAMP_MAX

On 13-Mar 17:29, Suren Baghdasaryan wrote:
> On Wed, Mar 13, 2019 at 9:16 AM Patrick Bellasi <patrick.bellasi@....com> wrote:
> >
> > On 13-Mar 15:12, Peter Zijlstra wrote:
> > > 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.
> >
> > Right, the code is clear enough, I'll remove this comment.
> 
> It would be probably even clearer if rq->uclamp_flags &=
> ~UCLAMP_FLAG_IDLE is done from inside uclamp_rq_inc after
> uclamp_rq_inc_id for both clamps is called.

Good point! I'll move it there to have something like:

---8<---
static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
{
	unsigned int clamp_id;

	if (unlikely(!p->sched_class->uclamp_enabled))
		return;

	for (clamp_id = 0; clamp_id < UCLAMP_CNT; ++clamp_id)
		uclamp_rq_inc_id(p, rq, clamp_id);

	/* Reset clamp holding when we have at least one RUNNABLE task */
	if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
		rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}
---8<---

-- 
#include <best/regards.h>

Patrick Bellasi