linux-kernel - Re: [PATCH 06/16] sched: SCHED

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Date:	Thu, 12 Apr 2012 08:51:49 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Juri Lelli <juri.lelli@...il.com>, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, cfriesen@...tel.com,
	oleg@...hat.com, fweisbec@...il.com, darren@...art.com,
	johan.eker@...csson.com, p.faure@...tech.ch,
	linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
	michael@...rulasolutions.com, fcheccon@...per.es
Subject: Re: [PATCH 06/16] sched: SCHED_DEADLINE push and pull logic

On Thu, 2012-04-12 at 20:28 +0800, Hillf Danton wrote:
> On Wed, Apr 11, 2012 at 10:10 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > 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.
> >

You're speaking in riddles.

> 	if (2 == dl_nr_migratory + dl_nr_total)
> 		rq was not overloaded;
> 
> 	after enqueuing a deadline task that is not migratory,

Now rq would be overloaded because:

	dl_nr_migratory + dl_nr_total == 3


> 
> 	if (current task is not preempted)
> 		rq remains not overloaded;

s/not//

> 
> 	else if (current task is not pushed out) {
> 		if (rq is not overloaded)
> 			maintenance of overloaded is __corrupted__;
> 	}
> 
> btw, same behavior in RTS?

I still don't understand what you are saying.

I can see your scenario happening with the change you are suggesting
though.

-- Steve


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