From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753258AbYJBINW (ORCPT ); Thu, 2 Oct 2008 04:13:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753797AbYJBING (ORCPT ); Thu, 2 Oct 2008 04:13:06 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:45407 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753850AbYJBINC (ORCPT ); Thu, 2 Oct 2008 04:13:02 -0400 Date: Thu, 2 Oct 2008 10:07:26 +0200 From: Ingo Molnar To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, laijs@cn.fujitsu.com, manfred@colorfullife.com, dipankar@in.ibm.com, niv@us.ibm.com, dvhltc@us.ibm.com, josht@linux.vnet.ibm.com Subject: Re: [PATCH,RFC] RCU-based detection of stalled CPUs for Classic RCU Message-ID: <20081002080726.GB17695@elte.hu> References: <20081002003628.GA7877@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081002003628.GA7877@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney wrote: > Hello! > > This patch adds stalled-CPU detection to Classic RCU. This capability > is enabled by a new config variable CONFIG_RCU_CPU_STALL_DETECTOR, > which defaults disabled. This is a debugging feature, not something > that non-kernel-hackers would be expected to care about. This feature > can detect looping CPUs in !PREEMPT builds and looping CPUs with > preemption disabled in PREEMPT builds. This is essentially a port of > this functionality from the treercu patch. > > One current shortcoming: on some systems, stalls are detected during > early boot, when we normally would not care about them. My thought is > to add a call from late initialization to suppress stall detection > until the system is well along its way to being booted, but thought I > should check to see if there might already be something for this > purpose. could you be a bit more specific, why do those warnings show up and why dont we care about them? There are things like networking that occasionally do an rcu_sync() and a stall could mean a bootup hang. > (Currently against 2.6.27-rc8, FYI.) > > Thoughts? > > Signed-off-by: Paul E. McKenney i think this is a very good idea in general - often the question comes up whether a hang seen in the RCU code is indeed caused by RCU or other factors. Could you perhaps rebase it against tip/core/rcu ? [or tip/master for convenience] Ingo