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Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space

To: Borislav Petkov <>,,,,,,,,,,,,,,,,,,,,,,
Subject: Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space
From: "Paul E. McKenney" <>
Date: Sun, 1 Apr 2012 11:11:15 -0700
In-reply-to: <20120401100448.GD14848@liondog.tnic>
References: <> <20120401100448.GD14848@liondog.tnic>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, Apr 01, 2012 at 12:04:48PM +0200, Borislav Petkov wrote:
> On Sun, Apr 01, 2012 at 12:33:21AM +0800, Paul E. McKenney wrote:
> > Although there have been numerous complaints about the complexity of
> > parallel programming (especially over the past 5-10 years), the plain
> > truth is that the incremental complexity of parallel programming over
> > that of sequential programming is not as large as is commonly believed.
> > Despite that you might have heard, the mind-numbing complexity of modern
> > computer systems is not due so much to there being multiple CPUs, but
> > rather to there being any CPUs at all.  In short, for the ultimate in
> > computer-system simplicity, the optimal choice is NR_CPUS=0.
> > 
> > This commit therefore limits kernel builds to zero CPUs.  This change
> > has the beneficial side effect of rendering all kernel bugs harmless.
> > Furthermore, this commit enables additional beneficial changes, for
> > example, the removal of those parts of the kernel that are not needed
> > when there are zero CPUs.
> > 
> > Signed-off-by: Paul E. McKenney <>
> > Reviewed-by: Thomas Gleixner <>
> Looks good, thanks for doing that.
> Btw, I just got confirmation from hw folk that we can actually give you
> hardware support for that code with an upcoming CPU which has NR_CPUS=0
> cores.
> Oh, and additionally, we can disable some of those so getting into the
> negative is also doable from the hw perspective, so feel free to explore
> that side of the problem too.
> ACK.

Cute!  ;-)

                                                        Thanx, Paul

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