From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Sat, 31 Mar 2012 23:23:18 +0200 (CEST) Received: from e1.ny.us.ibm.com ([32.97.182.141]:46555 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S1903702Ab2CaVXG (ORCPT ); Sat, 31 Mar 2012 23:23:06 +0200 Received: from /spool/local by e1.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 31 Mar 2012 17:23:00 -0400 Received: from d01dlp01.pok.ibm.com (9.56.224.56) by e1.ny.us.ibm.com (192.168.1.101) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Sat, 31 Mar 2012 17:22:02 -0400 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id 28E1238C8054 for ; Sat, 31 Mar 2012 17:22:01 -0400 (EDT) Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q2VLM0WN341192 for ; Sat, 31 Mar 2012 17:22:01 -0400 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q2VLLxvj015851 for ; Sat, 31 Mar 2012 15:22:00 -0600 Received: from paulmck-ThinkPad-W500 (sig-9-49-152-53.mts.ibm.com [9.49.152.53]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q2VLLwuW015844; Sat, 31 Mar 2012 15:21:58 -0600 Received: by paulmck-ThinkPad-W500 (Postfix, from userid 1000) id 235E9E4ABB; Sat, 31 Mar 2012 14:21:49 -0700 (PDT) Date: Sat, 31 Mar 2012 14:21:49 -0700 From: "Paul E. McKenney" To: Eric Dumazet Cc: linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, uclinux-dist-devel@blackfin.uclinux.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m32r@ml.linux-m32r.org, linux-m32r-ja@ml.linux-m32r.org, linux-mips@linux-mips.org, linux-am33-list@redhat.com, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, tglx@linutronix.de, linux@arm.linux.org.uk, dhowells@redhat.com, jejb@parisc-linux.org, linux390@de.ibm.com, x86@kernel.org, cmetcalf@tilera.com Subject: Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space Message-ID: <20120331212149.GI2450@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120331163321.GA15809@linux.vnet.ibm.com> <1333227608.2325.4054.camel@edumazet-glaptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1333227608.2325.4054.camel@edumazet-glaptop> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12033121-6078-0000-0000-0000099B4817 X-archive-position: 32845 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: paulmck@linux.vnet.ibm.com Precedence: bulk X-list: linux-mips Return-Path: 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 > > Reviewed-by: Thomas Gleixner > > --- > > 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