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

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Date:   Wed, 13 Mar 2019 18:29:55 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Peter Zijlstra <peterz@...radead.org>
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 13-Mar 18:29, Peter Zijlstra wrote:
> On Wed, Mar 13, 2019 at 04:20:51PM +0000, Patrick Bellasi wrote:
> > On 13-Mar 15:10, Peter Zijlstra wrote:
> > > On Fri, Feb 08, 2019 at 10:05:41AM +0000, Patrick Bellasi wrote:
> > > > +uclamp_idle_value(struct rq *rq, unsigned int clamp_id, unsigned int clamp_value)
> > > > +{
> > > > +	/*
> > > > +	 * Avoid blocked utilization pushing up the frequency when we go
> > > > +	 * idle (which drops the max-clamp) by retaining the last known
> > > > +	 * max-clamp.
> > > > +	 */
> > > > +	if (clamp_id == UCLAMP_MAX) {
> > > > +		rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
> > > > +		return clamp_value;
> > > > +	}
> > > > +
> > > > +	return uclamp_none(UCLAMP_MIN);
> > > 
> > > That's a very complicated way or writing: return 0, right?
> > 
> > In my mind it's just a simple way to hardcode values in just one place.
> > 
> > In the current implementation uclamp_none(UCLAMP_MIN) is 0 and the
> > compiler is not in trubles to inline a 0 there.
> > 
> > Is it really so disgusting ?
> 
> Not disguisting per se, just complicated. It had me go back and check
> wth uclamp_none() did again.

Yes, I see... every time I read it I just consider that uclamp_none()
it's just returning whatever is (or will be) the "non clamped" value
for the specified clamp index.

If it's ok with you, I would keep the code above as it is now.

-- 
#include <best/regards.h>

Patrick Bellasi