linux-kernel - Re: [Fwd: Re: RFC for a new Scheduling policy/class in the Linux-kernel]

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Message-ID: <alpine.LRH.2.00.0907161538340.3814@anderson.cs.unc.edu>
Date:	Thu, 16 Jul 2009 15:46:39 -0400 (EDT)
From:	"James H. Anderson" <anderson@...unc.edu>
To:	Raj Rajkumar <raj@....cmu.edu>
cc:	Ted Baker <baker@...fsu.edu>, Noah Watkins <jayhawk@....ucsc.edu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Raistlin <raistlin@...ux.it>,
	Douglas Niehaus <niehaus@...c.ku.edu>,
	Henrik Austad <henrik@...tad.us>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Bill Huey <billh@...ppy.monkey.org>,
	"Linux RT <linux-rt-users@...r.kernel.org> Fabio Checconi" 
	<fabio@...dalf.sssup.it>, Thomas Gleixner <tglx@...utronix.de>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Tommaso Cucinotta <cucinotta@...up.it>,
	Giuseppe Lipari <lipari@...is.sssup.it>,
	Bjoern Brandenburg <bbb@...unc.edu>,
	Karthik Singaram Lakshmanan <lakshmanan@....edu>,
	Dionisio de Niz <dionisio@....cmu.edu>
Subject: Re: [Fwd: Re: RFC for a new Scheduling policy/class in the
 Linux-kernel]

> It looks to me like Jim and Bjoern name the kernel-mutex locking scheme 
> (of non-preemption and FIFO queueing) as FMLP and advocate it for 
> user-level mutexes.  Jim: Please correct me if my interpretation is 
> incorrect.

I should have addressed this, sorry.

Actually, I don't advocate for anything.  :-)  As I said in my very
first email in this thread, in the LTIMUS^RT project, changing Linux
is not one of our goals.  I leave that to other people who are way
smarter than me.

But to the point you raise, please note that the long version of the
FMLP is a little more than combining non-preemption with FIFO waiting
since waiting is via suspension.  And as I said in an earlier email,
we designed it for a real-time (only) environment.  However, I think
a user-level variant that could be used in a more general environment
would certainly be possible.

-Jim

P.S. We didn't talk about the low processor utlization (Dhall effect)
mentioned in your last email.  However, that applies to hard real-time
workloads, not soft real-time workloads.  This discussion has been
touching on both.

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