linux-kernel - Re: [PATCH v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting

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Message-ID: <20190313194838.GS2482@worktop.programming.kicks-ass.net>
Date:   Wed, 13 Mar 2019 20:48:38 +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 01/15] sched/core: uclamp: Add CPU's clamp buckets
 refcounting

On Wed, Mar 13, 2019 at 04:12:29PM +0000, Patrick Bellasi wrote:
> On 13-Mar 14:40, Peter Zijlstra wrote:
> > On Fri, Feb 08, 2019 at 10:05:40AM +0000, Patrick Bellasi wrote:
> > > +static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
> > > +{
> > > +	return clamp_value / UCLAMP_BUCKET_DELTA;
> > > +}
> > > +
> > > +static inline unsigned int uclamp_bucket_value(unsigned int clamp_value)
> > > +{
> > > +	return UCLAMP_BUCKET_DELTA * uclamp_bucket_id(clamp_value);
> > 
> > 	return clamp_value - (clamp_value % UCLAMP_BUCKET_DELTA);
> > 
> > might generate better code; just a single division, instead of a div and
> > mult.
> 
> Wondering if compilers cannot do these optimizations... but yes, looks
> cool and will do it in v8, thanks.

I'd be most impressed if they pull this off. Check the generated code
and see I suppose :-)