From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f179.google.com (mail-we0-f179.google.com [74.125.82.179]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 915F4B6FD6 for ; Sun, 1 Apr 2012 07:00:17 +1000 (EST) Received: by werg1 with SMTP id g1so1026114wer.38 for ; Sat, 31 Mar 2012 14:00:13 -0700 (PDT) Subject: Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space From: Eric Dumazet To: paulmck@linux.vnet.ibm.com In-Reply-To: <20120331163321.GA15809@linux.vnet.ibm.com> References: <20120331163321.GA15809@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Sat, 31 Mar 2012 23:00:08 +0200 Message-ID: <1333227608.2325.4054.camel@edumazet-glaptop> Mime-Version: 1.0 Cc: linux-m32r-ja@ml.linux-m32r.org, linux-mips@linux-mips.org, linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org, dhowells@redhat.com, sparclinux@vger.kernel.org, linux-s390@vger.kernel.org, linux-am33-list@redhat.com, linux@arm.linux.org.uk, linux-hexagon@vger.kernel.org, x86@kernel.org, jejb@parisc-linux.org, cmetcalf@tilera.com, uclinux-dist-devel@blackfin.uclinux.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, linux-m32r@ml.linux-m32r.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux390@de.ibm.com, linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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.