linux-kernel - Re: [RFC][PATCH 05/22] sched: SCHED

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Date:	Thu, 11 Nov 2010 02:18:55 +0100
From:	Raistlin <raistlin@...ux.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Chris Friesen <cfriesen@...tel.com>, oleg@...hat.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Claudio Scordino <claudio@...dence.eu.com>,
	michael trimarchi <trimarchi@...is.sssup.it>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Tommaso Cucinotta <cucinotta@...up.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Nicola Manica <nicola.manica@...i.unitn.it>,
	Luca Abeni <luca.abeni@...tn.it>,
	Dhaval Giani <dhaval@...is.sssup.it>,
	Harald Gustafsson <hgu1972@...il.com>,
	paulmck <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 05/22] sched: SCHED_DEADLINE policy implementation

On Wed, 2010-11-10 at 21:21 +0100, Peter Zijlstra wrote:
> > +       if (dl_time_before(dl_se->deadline, rq->clock) ||
> > +           dl_entity_overflow(dl_se, rq->clock)) {
> > +               dl_se->deadline = rq->clock + dl_se->dl_deadline;
> > +               dl_se->runtime = dl_se->dl_runtime;
> > +       }
> > +} 
> 
> Can't we loose runtime deficit this way?
>
No, this should not be the case (I hope!). The rationale is basically
the same of the other e-mail about new instances.

In fact, a task that goes to sleep with some available runtime will be
given new parameters or not, depending on the return value of
dl_entity_overflow, and that's fine, right?

On the other hand, a task blocking while in overrun will (at dequeue_*
and/or put_* time) trigger the bandwidth enforcement logic (which arms
dl_timer) so that:
 - if unblocking happens _before_ it becomes eligible again, the 
   enqueue will be later handled by the dl_timer itself, when it'll
   fire, and the task will be given a replenishment starting from its
   negative runtime;
 - if unblocking happens _later_ than the firing of dl_timer, resetting
   the scheduling parameters should be just fine, from the bandwidth
   point of view.

Does it make sense?

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa  (Italy)

http://blog.linux.it/raistlin / raistlin@...ga.net /
dario.faggioli@...ber.org

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