linux-kernel - Re: periods and deadlines in SCHED

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Date:	Fri, 09 Jul 2010 16:30:00 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Raistlin <raistlin@...ux.it>
Cc:	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>,
	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 15:38 +0200, Raistlin wrote:
> 
> Therefore, here it is my proposal:
>  - if the programmer specify both period and deadline, I act as above,
>    running the _only_necessary_ test in the kernel, assuming that
>    userspace performed some other kind of (correct!) admission test by
>    its own, or that it is cool with missing some deadlines... What do
>    you think?

It would be good to provide room in the interface to improve upon this
situation.

One thing we could do, although this would make the proposed scheduler a
wee bit more complex, is split between hard and soft realtime. Only
accept P==rel_D for hard, and schedule the soft tasks in the hard slack
or something like that.

That way we can later extend the hard admission tests to accept more.

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