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

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Date:   Fri, 21 Apr 2017 09:39:48 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     luca abeni <luca.abeni@...tannapisa.it>
Cc:     Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        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 Fri, 21 Apr 2017 11:54:21 +0200
luca abeni <luca.abeni@...tannapisa.it> wrote:

> On Fri, 21 Apr 2017 11:42:40 +0200
> luca abeni <luca.abeni@...tannapisa.it> wrote:
> [...]
> > > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > > > index a2ce590..ec53d24 100644
> > > > --- a/kernel/sched/deadline.c
> > > > +++ b/kernel/sched/deadline.c
> > > > @@ -950,6 +950,10 @@ enqueue_dl_entity(struct sched_dl_entity
> > > > *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...  
> 
> __sched_setscheduler() sets queue_flags to DEQUEUE_SAVE, which matches
> ENQUEUE_RESTORE (see comments in sched/sched.h), so things should work
> correctly, right?

I was tripping over this too, but missed the comments in sched/sched.h.

Probably want to stick a comment about this in here as well.

-- Steve