linux-kernel - Re: [PATCH] sched/deadline: fix switching to -deadline

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Message-ID: <20170421102659.GS23862@e106622-lin>
Date:   Fri, 21 Apr 2017 11:26:59 +0100
From:   Juri Lelli <juri.lelli@....com>
To:     luca abeni <luca.abeni@...tannapisa.it>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH] sched/deadline: fix switching to -deadline

On 21/04/17 11:59, Luca Abeni wrote:
> On Fri, 21 Apr 2017 10:47:29 +0100
> Juri Lelli <juri.lelli@....com> wrote:
> [...]
> > > > > *dl_se, update_dl_entity(dl_se, pi_se);
> > > > >  	else if (flags & ENQUEUE_REPLENISH)
> > > > >  		replenish_dl_entity(dl_se, pi_se);
> > > > > +	else if ((flags & ENQUEUE_RESTORE) &&    
> > > > 
> > > > Not sure I understand how this works. AFAICT we are doing
> > > > __sched_setscheduler() when we want to catch the case of a new
> > > > dl_entity (SCHED_{OTHER,FIFO} -> SCHED_DEADLINE}, but queue_flags
> > > > (which are passed to enqueue_task()) don't seem to have
> > > > ENQUEUE_RESTORE set?  
> > > 
> > > I was under the impression sched_setscheduler() sets
> > > ENQUEUE_RESTORE... 
> > 
> > Oh, I think it works "by coincidence", as ENQUEUE_RESTORE ==
> > DEQUEUE_SAVE == 0x02 ? :)
> 
> Not sure if this is a conincidence... By looking at the comments in
> sched/sched.h I got the impression the two values match by design (and
> __sched_setscheduler() is using this property to simplify the code :)
> 

Yep, right.

Do you think we might get into trouble with do_set_cpus_allowed()?
Can it happen that we change a task affinity while its deadline is in
the past?