linux-kernel - Re: periods and deadlines in SCHED

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Message-ID: <1280828475.1923.444.camel@laptop>
Date:	Tue, 03 Aug 2010 11:41:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Bjoern Brandenburg <bbb@...il.unc.edu>
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>,
	Luca Abeni <lucabe72@...il.it>,
	Claudio Scordino <claudio@...dence.eu.com>,
	Harald Gustafsson <harald.gustafsson@...csson.com>,
	bastoni@...unc.edu, Giuseppe Lipari <lipari@...is.sssup.it>
Subject: Re: periods and deadlines in SCHED_DEADLINE

On Sun, 2010-07-11 at 08:42 +0200, Bjoern Brandenburg wrote:
> 
> If you want to do G-EDF with limited and different budgets on each CPU
> (e.g., G-EDF tasks may only run for 100 out of 1000 ms on CPU 0, but
> for 400 out of 1000 ms on CPU 1), then you are entering the domain of
> restricted-supply scheduling, which is significantly more complicated
> to analyze (see [1,2]). 

Without having looked at the refs, won't the soft case still have
bounded tardiness? Since the boundedness property mostly depends on
u<=1, that is, as long as we can always run everything within the
available time we won't start drifting.

> As far as I know there is no exiting analysis for "almost G-EDF",
> i.e.,  the case where each task may only migrate among a subset of the
> processors (= affinity masks), except for the special case of
> clustered EDF (C-EDF), wherein the subsets of processors are
> non-overlapping. 

Right, affinity masks are a pain, hence I proposed to limit that to
either 1 cpu (yielding fully paritioned) or the full cluster.

That will leave us with only having to stack a partitioned and global
scheduler on top of each other, and per the previous point, I think that
ought to work out trivially for soft, hard otoh will get 'interesting'.


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