From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752415Ab1EPHjl (ORCPT ); Mon, 16 May 2011 03:39:41 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:42860 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751758Ab1EPHji (ORCPT ); Mon, 16 May 2011 03:39:38 -0400 Date: Mon, 16 May 2011 09:39:28 +0200 From: Ingo Molnar To: "Paul E. McKenney" Cc: Yinghai Lu , linux-kernel@vger.kernel.org Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40 Message-ID: <20110516073928.GA23252@elte.hu> References: <20110514142621.GB2258@linux.vnet.ibm.com> <20110514153118.GA24311@linux.vnet.ibm.com> <20110514183453.GA32756@linux.vnet.ibm.com> <4DCF5322.7030305@kernel.org> <4DCF6789.70701@kernel.org> <4DCF696B.8020304@kernel.org> <20110515060415.GF2258@linux.vnet.ibm.com> <20110515065949.GA11330@linux.vnet.ibm.com> <20110516070849.GA20580@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110516070849.GA20580@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes 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: > > And the way you can prove that it is my code rather than the arch > > code is to show that the warning happens on your system when the > > irq_enter()/irq_exit() calls are perfectly nested. > > So I took another look at the RCU debugfs stats you provided earlier, > and realized that your system gets a lot more NMIs than do the ones > that I have access to. So as a diagnostic patch, I ifdefed out the > body of rcu_nmi_enter() and rcu_nmi_exit(). Well, but the delays are occuring all the time (and it's bisectable) and NMIs are generally not deterministic. I'd really suggest the creation of a revert + finegrained series on top of core/rcu which would IMHO help us narrow this down a lot more directly than jumping between the 'need_resched bug', 'nmi bug' and 'barrier bug' hypoteses. ( Btw., the bug still has the feeling of a need_resched/scheduling/timing artifact to me, not barriers or NMI. ) Thanks, Ingo