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Subject: Re: [PATCH 06/16] sched: SCHED_DEADLINE push and pull logic
From: Steven Rostedt <rostedt@goodmis.org>
To: Hillf Danton <dhillf@gmail.com>
Cc: Juri Lelli <juri.lelli@gmail.com>, peterz@infradead.org,
        tglx@linutronix.de, mingo@redhat.com, cfriesen@nortel.com,
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Date: Wed, 11 Apr 2012 10:10:50 -0400
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On Fri, 2012-04-06 at 21:39 +0800, Hillf Danton wrote:

> > +static void inc_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> > +{
> > +       dl_rq = &rq_of_dl_rq(dl_rq)->dl;
> > +
> > +       dl_rq->dl_nr_total++;
> > +       if (dl_se->nr_cpus_allowed > 1)
> > +               dl_rq->dl_nr_migratory++;
> > +
> > +       update_dl_migration(dl_rq);
> 
> 	if (dl_se->nr_cpus_allowed > 1) {
> 		dl_rq->dl_nr_migratory++;
> 		/* No change in migratory, no update of migration */

This is not true. As dl_nr_total changed. If there was only one dl task
queued that can migrate, and then another dl task is queued but this
task can not migrate, the update_dl_migration still needs to be called.
As dl_nr_migratory would be 1, but now dl_nr_total > 1. This means we
are now overloaded.

> 		update_dl_migration(dl_rq);
> 	}
> 
> > +}
> > +
> > +static void dec_dl_migration(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> > +{
> > +       dl_rq = &rq_of_dl_rq(dl_rq)->dl;
> > +
> > +       dl_rq->dl_nr_total--;
> > +       if (dl_se->nr_cpus_allowed > 1)
> > +               dl_rq->dl_nr_migratory--;
> > +
> > +       update_dl_migration(dl_rq);
> 
> ditto

ditto.

> 
> > +}
> > +
> > +/*
> > + * The list of pushable -deadline task is not a plist, like in
> > + * sched_rt.c, it is an rb-tree with tasks ordered by deadline.

-- Steve