From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH RFC] Simplify the Linux kernel by reducing its state space Date: Sat, 31 Mar 2012 18:22:12 -0700 Message-ID: <20120401012212.GP2450@linux.vnet.ibm.com> References: <20120331163321.GA15809@linux.vnet.ibm.com> <20120331223200.GA32482@n2100.arm.linux.org.uk> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20120331223200.GA32482@n2100.arm.linux.org.uk> Sender: linux-alpha-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Russell King - ARM Linux 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, dhowells@redhat.com, jejb@parisc-linux.org, linux390@de.ibm.com, x86@kernel.org, cmetcalf@tilera.com On Sat, Mar 31, 2012 at 11:32:00PM +0100, Russell King - ARM Linux 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 > > Great work, but I don't think you've gone far enough with this. > > What would really help is if you could consolidate all these NR_CPUS > definitions into one place so we don't have essentially the same thing > scattered across all these architectures. We're already doing this on > ARM across our platforms, and its about time such an approach was taken > across the entire kernel tree. > > It looks like the MIPS solution would be the best one to pick. > Could you rework your patch to do this please? > > While you're at it, you might like to consider that having zero CPUs > makes all this architecture support redundant, so maybe you've missed > a trick there - according to my count, we could get rid of almost 3 > million lines of code from arch. We could replace all that with a > single standard implementation. > > Bah, maybe I shouldn't have pushed that bpf_jit code for ARM after all... ;-) ;-) ;-) Thanx, Paul