linux-kernel - Re: [PATCH RFC 3/8] sched/cpufreq_schedutil: make worker kthread be SCHED

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Date:   Wed, 24 May 2017 10:31:40 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, rjw@...ysocki.net, viresh.kumar@...aro.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        tglx@...utronix.de, vincent.guittot@...aro.org,
        rostedt@...dmis.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org, tkjos@...roid.com,
        joelaf@...gle.com, andresoportus@...gle.com,
        morten.rasmussen@....com, dietmar.eggemann@....com,
        patrick.bellasi@....com, Ingo Molnar <mingo@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH RFC 3/8] sched/cpufreq_schedutil: make worker kthread be
 SCHED_DEADLINE

Hi,

On 23/05/17 20:52, Peter Zijlstra wrote:
> On Tue, May 23, 2017 at 09:53:46AM +0100, Juri Lelli wrote:
> > diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
> > index e2a6c7b3510b..72723859ef74 100644
> > --- a/include/uapi/linux/sched.h
> > +++ b/include/uapi/linux/sched.h
> > @@ -48,5 +48,6 @@
> >   */
> >  #define SCHED_FLAG_RESET_ON_FORK	0x01
> >  #define SCHED_FLAG_RECLAIM		0x02
> > +#define SCHED_FLAG_SPECIAL		0x04
> >  
> >  #endif /* _UAPI_LINUX_SCHED_H */
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 7fc2011c3ce7..ba57e2ef9aef 100644
> 
> > @@ -4205,7 +4212,9 @@ static int __sched_setscheduler(struct task_struct *p,
> >  	}
> >  
> >  	if (attr->sched_flags &
> > -		~(SCHED_FLAG_RESET_ON_FORK | SCHED_FLAG_RECLAIM))
> > +		~(SCHED_FLAG_RESET_ON_FORK |
> > +		  SCHED_FLAG_RECLAIM |
> > +		  SCHED_FLAG_SPECIAL))
> >  		return -EINVAL;
> >  
> >  	/*
> 
> Could we pretty please not expose this gruesome hack to userspace?
> 
> So if you stick it in attr->sched_flags, use a high bit and don't put it
> in a uapi header. Also make the flags check explicitly fail on it when
> @user. Such that only _nocheck() (and thus kernel) callers have access
> to it.
>

Sure, I should have done it in the first place.

> Also, there's not nearly enough warnings and other derisory comments
> near it.

Eheh, I'll add all the derisory remarks I'm capable of. :/

Thanks,

- Juri