From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757406Ab1EZQ2I (ORCPT ); Thu, 26 May 2011 12:28:08 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:42090 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751638Ab1EZQ2G (ORCPT ); Thu, 26 May 2011 12:28:06 -0400 Date: Thu, 26 May 2011 09:28:02 -0700 From: "Paul E. McKenney" To: Yinghai Lu Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, tglx@linutronix.de, mingo@elte.hu Subject: Re: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof" Message-ID: <20110526162802.GC2386@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110524013523.GO7428@linux.vnet.ibm.com> <4DDC21E1.1070502@kernel.org> <4DDC48E3.1060108@kernel.org> <20110525045253.GB2262@linux.vnet.ibm.com> <4DDD7F96.3090408@kernel.org> <20110525223437.GO2341@linux.vnet.ibm.com> <4DDD8775.1000501@kernel.org> <20110526011310.GP2341@linux.vnet.ibm.com> <20110526013029.GA28103@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 26, 2011 at 08:08:26AM -0700, Yinghai Lu wrote: > On Wed, May 25, 2011 at 6:30 PM, Paul E. McKenney > wrote: > > On Wed, May 25, 2011 at 06:13:10PM -0700, Paul E. McKenney wrote: > >> On Wed, May 25, 2011 at 03:49:25PM -0700, Yinghai Lu wrote: > >> > On 05/25/2011 03:34 PM, Paul E. McKenney wrote: > >> > > On Wed, May 25, 2011 at 03:15:50PM -0700, Yinghai Lu wrote: > >> > >>> There is a new branch yinghai.2011.05.24a on: > >> > >>> > >> > >>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu.git > >> > >>> > >> > >>> Or will be as soon as kernel.org updates its mirrors. > >> > >>> > >> > >>> I am not sure I could call this "clean", but it does revert that commit > >> > >>> and 11 of the subsequent commits that depend on it.  It does build, > >> > >>> and I will test it once my currently running tests complete. > >> > >> > >> > >> yes, with those revert, there is no delay in 10 times booting. > >> > > > >> > > Unfortunately, there are rcutorture test failures with the revert... > >> > > >> > confused. > >> > >> Given what I had to do to generate the revert, not exactly a surprise, > >> I am afraid.  Just means that the resulting RCU sometimes fails to > >> wait for all pre-existing readers, and rcutorture catches it. > >> > >> > what is the next? > >> > >> 1.    I send you a patch that I hope will fix the softlockup > >>       you saw.  I am testing this. > >> > >> 2.    I am working on more detailed instrumentation, and will > >>       send a patch on that. > >> > >> 3.    If time allows, break down the operations RCU is doing > >>       and test them in isolation. > >> > >> Other thoughts? > > > > And here is patch #1.  Could you please try applying this on top of > > Peter Zijlstra's patch to see if it gets rid of the softlockups you saw? > > > >                                                        Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > rcu: Start RCU kthreads in TASK_INTERRUPTIBLE state > > > > Upon creation, kthreads are in TASK_UNINTERRUPTIBLE state, which can > > result in softlockup warnings.  Because some of RCU's kthreads can > > legitimately be idle indefinitely, start them in TASK_INTERRUPTIBLE > > state in order to avoid those warnings. > > Yes, it fixes the lock up warning. Very good, I have added your Tested-by. Thanx, Paul