linux-kernel - Re: periods and deadlines in SCHED

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Message-Id: <4C57C8580200005A0006E50B@soto.provo.novell.com>
Date:	Tue, 03 Aug 2010 05:42:16 -0600
From:	"Gregory Haskins" <ghaskins@...ell.com>
To:	"Bjoern Brandenburg" <bbb@...il.unc.edu>,
	"Peter Zijlstra" <peterz@...radead.org>
Cc:	<bastoni@...unc.edu>,
	"Nicola Manica" <nicola.manica@...i.unitn.it>,
	"Luca Abeni" <lucabe72@...il.it>,
	"Harald Gustafsson" <harald.gustafsson@...csson.com>,
	"Song Yuan" <song.yuan@...csson.com>,
	"Claudio Scordino" <claudio@...dence.eu.com>,
	"Dmitry Adamushko" <dmitry.adamushko@...il.com>,
	"rostedt" <rostedt@...dmis.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Raistlin" <raistlin@...ux.it>,
	"Giuseppe Lipari" <lipari@...is.sssup.it>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: periods and deadlines in SCHED_DEADLINE

Hello Peter, Steven, Thomas, et al. !

Its been a while.

>>> On 8/3/2010 at 04:16 AM, in message <1280823360.1923.419.camel@...top>, Peter
Zijlstra <peterz@...radead.org> wrote: 

[snip]

>
> So we replace the global lock with cmpxchg like loops using 2 per-cpu
> locks. Our current SCHED_FIFO balancer does just this and is found to be
> a very good approximation of global-fifo (iirc there's one funny case,
> but I can't remember, maybe Steve or Gregory can remember the details).

The only thing I remember at the moment is that Steven and I found one last remaining bug in an extreme corner
case where priority order may be violated.  Sadly, I can no longer recall the exact specifics and would have to dig
into the code to remember.  The good news is I believe the issue is fixable.  Its just a matter of impl+test, which
neither of us ever seem to have found the time to properly dedicate.  Perhaps this will be the catalyst ;)

-Greg


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