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

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Date:	Mon, 23 Nov 2009 15:08:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jon Tore Hafstad <jontore@...il.com>
Cc:	linux-kernel@...r.kernel.org, dhaval.giani@...il.com,
	mingo@...e.hu, tglx@...utronix.de, bbb@...unc.edu,
	henrik@...tad.us, jmc@...unc.edu, Jeff Dike <jdike@...toit.com>
Subject: Re: LinSched updated to current linux kernel version

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).

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..

But I suspect that with KVM's gdb stub getting usable more and more
people are abandoning this.

> == Remaining Work ==
> One of the major issues right now is the hrtimers, which large
> portions of the scheduler now use. I have not decided exactly how to
> solve this issue yet,but this will be the focus of my work for the
> coming weeks.

The typical implementation would be signals using the posix timers.

Have the spin_lock_irq variants mask signals etc..

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