From patchwork Sun Apr 1 17:34:55 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thomas Gleixner X-Patchwork-Id: 149964 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 12B51B6EE7 for ; Mon, 2 Apr 2012 03:35:27 +1000 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752753Ab2DARfK (ORCPT ); Sun, 1 Apr 2012 13:35:10 -0400 Received: from www.linutronix.de ([62.245.132.108]:46839 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751601Ab2DARfH (ORCPT ); Sun, 1 Apr 2012 13:35:07 -0400 Received: from localhost ([127.0.0.1]) by Galois.linutronix.de with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from ) id 1SEOg5-00051j-Aw; Sun, 01 Apr 2012 19:34:57 +0200 Date: Sun, 1 Apr 2012 19:34:55 +0200 (CEST) From: Thomas Gleixner To: Russell King - ARM Linux cc: "Paul E. McKenney" , 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, 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 In-Reply-To: <20120331223200.GA32482@n2100.arm.linux.org.uk> Message-ID: References: <20120331163321.GA15809@linux.vnet.ibm.com> <20120331223200.GA32482@n2100.arm.linux.org.uk> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1, SHORTCIRCUIT=-0.0001 Sender: sparclinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: sparclinux@vger.kernel.org On Sat, 31 Mar 2012, 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. For a first step we can deprecated arch/ and make it depend on CONFIG_STAGING. That way we can have it around a bit for sentimental reasons w/o having a lot of churn. Suggested-by: Russell King Signed-off-by: Thomas Gleixner Reviewed-by: Paul E. McKenney --- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Index: tip/Makefile =================================================================== --- tip.orig/Makefile +++ tip/Makefile @@ -564,7 +564,9 @@ else KBUILD_CFLAGS += -O2 endif +ifdef CONFIG_ARCH_SUPPORT include $(srctree)/arch/$(SRCARCH)/Makefile +endif ifneq ($(CONFIG_FRAME_WARN),0) KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN}) Index: tip/drivers/staging/Kconfig =================================================================== --- tip.orig/drivers/staging/Kconfig +++ tip/drivers/staging/Kconfig @@ -1,6 +1,10 @@ +config ARCH_SUPPORT + bool + menuconfig STAGING bool "Staging drivers" default n + select ARCH_SUPPORT ---help--- This option allows you to select a number of drivers that are not of the "normal" Linux kernel quality level. These drivers Index: tip/Documentation/feature-removal-schedule.txt =================================================================== --- tip.orig/Documentation/feature-removal-schedule.txt +++ tip/Documentation/feature-removal-schedule.txt @@ -537,3 +537,13 @@ When: 3.6 Why: setitimer is not returning -EFAULT if user pointer is NULL. This violates the spec. Who: Sasikantha Babu + +----------------------------- + +What: Remove arch +When: April 1st 2013 +Why: NR_CPUS=0 made arch/ obsolete. Keep it around a bit for + sentimental reasons. +Who: paulmck,tglx.rmk + +