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

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Date:	Sat, 31 Mar 2012 14:21:49 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	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 Sat, Mar 31, 2012 at 11:00:08PM +0200, Eric Dumazet wrote:
> On Sun, 2012-04-01 at 00:33 +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>
> > ---
> 
> Hmm... I believe you could go one step forward and allow negative values
> as well. Antimatter was proven to exist after all.
> 
> Hint : nr_cpu_ids is an "int", not an "unsigned int"
> 
> Bonus: Existing bugs become "must have" features.

;-) ;-) ;-)

> Of course there is no hurry and this can wait 365 days.

James Bottomley suggested imaginary numbers of CPUs some time back,
and I suppose there is no reason you cannot have fractional numbers of
CPUs, and perhaps irrational numbers as well.  Of course, these last two
would require use of floating-point arithmetic (or something similar)
in the kernel.  So I guess we have at several years worth.  Over to you
for the negative numbers.  ;-)

							Thanx, Paul

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