From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751639AbZHIFdM (ORCPT ); Sun, 9 Aug 2009 01:33:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751312AbZHIFdM (ORCPT ); Sun, 9 Aug 2009 01:33:12 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:37140 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbZHIFdL (ORCPT ); Sun, 9 Aug 2009 01:33:11 -0400 Date: Sat, 8 Aug 2009 22:33:08 -0700 From: "Paul E. McKenney" To: Hugh Dickins Cc: Ingo Molnar , Ben Herrenschmidt , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: CONFIG_PREEMPT_RCU in next/mmotm Message-ID: <20090809053308.GD6866@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20090808235634.GB6866@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 04:32:28AM +0100, Hugh Dickins wrote: > On Sat, 8 Aug 2009, Paul E. McKenney wrote: > > On Sat, Aug 08, 2009 at 08:34:03PM +0100, Hugh Dickins wrote: > > > > > CONFIG_PREEMPT_TREE=y seems okay on PowerPC; and when I briefly tried > > > > CONFIG_TREE_RCU=y, you mean, right? > > Whoops, yes indeed. > > > > My guess is that there's some other issue which is triggering > > > the RCU disgrace, but that is just a guess. > > > > The one other issue I know of is one that apparently happens only on > > one of Ingo's machines, which suddenly decides that it need not inform > > RCU when onlining a CPU (at boot time). > > > > But you seem to be making it past boot, and I would guess that you are > > not doing any hotplug CPU operations, right? > > That's right, I'm well past boot, and don't explicitly get into CPU > hotplug, nor using suspend/hibernate on that machine; and looking at > the config, see I don't even have CONFIG_HOTPLUG_CPU set. > > In the morning I'll check that /proc/cpuinfo really shows all four > cpus before I start, and is still showing four cpus when it goes bad, > in case there's nevertheless an issue with that. > > Is there some particular attribute of a cpu, most relevant to its RCU > grace status, that I can check on with a printk? The debugfs files enabled by CONFIG_RCU_TRACE, except rcu/rcugp, which, since it will attempt to wait for a grace period, will probably wait forever. > > > Config attached. Any suggestions? > > [ Of course I forgot the config, but sent it just to Paul later. ] > > > > > /me scratches head... Will try some more CONFIG_PREEMPT_RCU testing > > locally. > > Thanks: I'm kind of glad that it's interesting, > though it may sink some of our time. Well, it certainly does have me a bit confused at the moment! Thanx, Paul