From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752735AbZHITXq (ORCPT ); Sun, 9 Aug 2009 15:23:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752368AbZHITXq (ORCPT ); Sun, 9 Aug 2009 15:23:46 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:34520 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751891AbZHITXp (ORCPT ); Sun, 9 Aug 2009 15:23:45 -0400 Date: Sun, 9 Aug 2009 12:23:45 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:core/rcu] rcu: Add second diagnostic check for a possible CPU-hotplug race Message-ID: <20090809192345.GA19433@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090806012645.GA24800@linux.vnet.ibm.com> <20090809110019.GA20236@elte.hu> <20090809111008.GA1829@elte.hu> <20090809183010.GF6866@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090809183010.GF6866@linux.vnet.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 09, 2009 at 11:30:10AM -0700, Paul E. McKenney wrote: > On Sun, Aug 09, 2009 at 01:10:08PM +0200, Ingo Molnar wrote: > > > > * Ingo Molnar wrote: > > > > > > rcu: Add second diagnostic check for a possible CPU-hotplug race > > > > > > has a build problem too: > > > > > > kernel/built-in.o: In function `rcu_cpu_notified': > > > (.text+0x1d787): undefined reference to `cpu_notified' > > > kernel/built-in.o: In function `rcu_init': > > > (.init.text+0x1174): undefined reference to `cpu_notified' > > > kernel/built-in.o: In function `rcu_init': > > > (.init.text+0x11a8): undefined reference to `cpu_notified' > > > > > > Maybe we should simplify all those Kconfig rules? It's a maze. > > Or I could fix up my scripts so that I once again test the relevant > combinations -before- I submit the patch. :-/ That said, I could imagine the following simplifications: o CONFIG_SMP always implies CONFIG_HOTPLUG_CPU, eliminating the need to test CONFIG_SMP&&!CONFIG_HOTPLUG_CPU. o Make CONFIG_NO_HZ unconditional. (Now, -that- should get a reaction! For one thing, I am not sure that all architectures support CONFIG_NO_HZ.) o Eliminate the combination CONFIG_PREEMPT && CONFIG_TREE_RCU. In other words, make a preemptable kernel imply preemptable RCU and vice versa. o After sufficient testing, eliminate CONFIG_PREEMPT_RCU in favor of CONFIG_TREE_PREEMPT_RCU (currently under development). o After sufficient testing, make !CONFIG_SMP imply CONFIG_TINY_RCU. This might require a preemptable variant of CONFIG_TINY_RCU. There are probably quite a few similar simplifications. Thanx, Paul