linux-kernel - Re: LinSched updated to current linux kernel version

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Message-Id: <200911232102.07419.henrik@austad.us>
Date:	Mon, 23 Nov 2009 21:02:03 +0100
From:	Henrik Austad <henrik@...tad.us>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jon Tore Hafstad <jontore@...il.com>, linux-kernel@...r.kernel.org,
	dhaval.giani@...il.com, mingo@...e.hu, tglx@...utronix.de,
	bbb@...unc.edu, jmc@...unc.edu, Jeff Dike <jdike@...toit.com>
Subject: Re: LinSched updated to current linux kernel version

On Monday 23. November 2009 15.08.15 Peter Zijlstra wrote:
> On Wed, 2009-11-18 at 21:11 +0100, Jon Tore Hafstad wrote:
> >  Hi all
> >
> > I wish to inform you about an update of LinSched (The Linux Scheduler
> > Simulator([1])) I'm currently working on.
> >
> > == Motivation ==
> > I wished to implement different EDF schedulers to gain a better
> > understanding of kernel internals as well as scheduling dynamics. I
> > got some feedback from Henrik Austad  that LinSched was a tool that
> > made implementing a scheduler in to  the linux kernel easier,  since
> > the code compiles in a fraction of the time the kernel does (Yes, I
> > know you can pull all sorts of tricks and tweaks in order to speed up
> > a kernel compilation), a segfault will be a segfault, and not a kernel
> > oops ;),and the full range of debuggers and memory analyzers will be
> > available.
> 
> I would have expected people to use UML for this (User-Mode-Linux, not
> the draw lots of silly pictures thing).

What is the current status of UML - is anyone actually working on that these 
days?

> The main draw-back is that UML doesn't currently support SMP and any
> interesting preemption modes, but adding that to UML would help out more
> people -- I know the VM (virtual Memory, not the machine thing) people
> used to use UML for exactly these reasons, easy gdb, etc..

Well, another drawback of UML is the size. The whole point with LinSched is to 
be *lightweight* while still being accurate. By accurate I mean that code 
written and tested with LinSched should work nearly out of the box when placed 
in the kernel.

LinSched is all about scheduling - nothing else. To be able to compile the 
code in a fraction of a second, and then simulate hours worth of computing (or 
at least the task-switches) can be *very* useful. 

IMHO, making it easy to test new scheduling algorithms is a very neat way of 
attracting new kernel/scheduler hackers (as well as testing all sorts of crazy 
algorithms).

Just my $0.02

-- 
     henrik

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