linux-kernel - Re: periods and deadlines in SCHED

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Message-Id: <1278745907.5248.18.camel@localhost>
Date:	Sat, 10 Jul 2010 09:11:47 +0200
From:	Luca Abeni <lucabe72@...il.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Raistlin <raistlin@...ux.it>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Song Yuan <song.yuan@...csson.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nicola Manica <nicola.manica@...i.unitn.it>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	Bjoern Brandenburg <bbb@...il.unc.edu>, bastoni@...unc.edu,
	Giuseppe Lipari <lipari@...is.sssup.it>
Subject: Re: periods and deadlines in SCHED_DEADLINE

On Fri, 2010-07-09 at 16:24 +0200, Peter Zijlstra wrote:
> On Fri, 2010-07-09 at 15:38 +0200, Raistlin wrote:
> > Basically, from the scheduling point of view, what it could happen is
> > that I'm still _NOT_ going to allow a task with runtime Q_i, deadline
> > D_i and period P_i to use more bandwidth than Q_i/P_i, I'm still using D
> > for scheduling but the passing of the simple in-kernel admission test
> > Sum_i(Q_i/P_i)<1 won't guarantee that the task will always finish its
> > jobs before D. 
> 
> But the tardiness would still be bounded, right? So its a valid Soft-RT
> model?
I think that if Sum_i(Q_i/P_i)<1 but Sum_i(Q_i/min{P_i,D_i})>=1 then you
can have sporadic deadline misses, but it should still be possible to
compute an upper bound for the tardiness.
But this is just a feeling, I have no proof... :)


				Luca

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