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

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Message-ID: <20120401181114.GY2450@linux.vnet.ibm.com>
Date:	Sun, 1 Apr 2012 11:11:15 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
	linux-m32r@...linux-m32r.org, linux-m32r-ja@...linux-m32r.org,
	linux-mips@...ux-mips.org, linux-am33-list@...hat.com,
	linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	sparclinux@...r.kernel.org, tglx@...utronix.de,
	linux@....linux.org.uk, dhowells@...hat.com, jejb@...isc-linux.org,
	linux390@...ibm.com, x86@...nel.org, cmetcalf@...era.com
Subject: Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space

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 <paulmck@...ux.vnet.ibm.com>
> > Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
> 
> 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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