linux-kernel - Re: [PATCH v8 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping

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Message-ID: <20190508194439.GF32547@worktop.programming.kicks-ass.net>
Date:   Wed, 8 May 2019 21:44:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        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 v8 06/16] sched/core: uclamp: Extend sched_setattr() to
 support utilization clamping

On Tue, May 07, 2019 at 12:13:47PM +0100, Patrick Bellasi wrote:
> On 17-Apr 15:26, Suren Baghdasaryan wrote:
> > On Tue, Apr 2, 2019 at 3:42 AM Patrick Bellasi <patrick.bellasi@....com> wrote:

> > > @@ -1056,6 +1100,13 @@ static void __init init_uclamp(void)
> > >  #else /* CONFIG_UCLAMP_TASK */
> > >  static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
> > >  static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
> > > +static inline int uclamp_validate(struct task_struct *p,
> > > +                                 const struct sched_attr *attr)
> > > +{
> > > +       return -ENODEV;
> > 
> > ENOSYS might be more appropriate?
> 
> Yep, agree, thanks!

No, -ENOSYS (see the comment) is special in that it indicates the whole
system call is unavailable; that is most certainly not the case!