From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755637Ab1IMQtn (ORCPT ); Tue, 13 Sep 2011 12:49:43 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:44356 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754159Ab1IMQtm (ORCPT ); Tue, 13 Sep 2011 12:49:42 -0400 Date: Tue, 13 Sep 2011 09:49:33 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: LKML , David Miller , Chris Metcalf , Guan Xuetao , Hans-Christian Egtvedt , Mike Frysinger , Ralf Baechle , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , "H. Peter Anvin" , Russell King , Paul Mackerras , Heiko Carstens , Paul Mundt Subject: Re: [PATCH 1/4] nohz: Split extended quiescent state handling from nohz switch Message-ID: <20110913164933.GF2416@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1313861452-24783-1-git-send-email-fweisbec@gmail.com> <1313861452-24783-2-git-send-email-fweisbec@gmail.com> <20110904233643.GN2411@linux.vnet.ibm.com> <20110907142233.GA11570@linux.vnet.ibm.com> <20110913000637.GA17335@somewhere.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110913000637.GA17335@somewhere.redhat.com> 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 Tue, Sep 13, 2011 at 02:06:45AM +0200, Frederic Weisbecker wrote: > On Wed, Sep 07, 2011 at 07:22:33AM -0700, Paul E. McKenney wrote: > > On Sun, Sep 04, 2011 at 04:36:43PM -0700, Paul E. McKenney wrote: > > > On Sat, Aug 20, 2011 at 07:30:49PM +0200, Frederic Weisbecker wrote: > > > > It is assumed that rcu won't be used once we switch to tickless > > > > mode and until we restart the tick. However this is not always > > > > true, as in x86-64 where we dereference the idle notifiers after > > > > the tick is stopped. > > > > > > > > To prepare for fixing this, split the tickless mode switching and > > > > RCU extended quiescent state logics. > > > > Make tick_nohz_stop/restart_sched_tick() RCU agnostic but provide > > > > a new pair of APIs tick_nohz_enter/exit_idle() that keep the > > > > old behaviour by handling both the nohz mode and RCU extended > > > > quiescent states, then convert every archs to use these. > > > > > > > > Archs that want to switch to RCU extended QS to some custom points > > > > can do it later by changing the parameter in tick_nohz_enter,exit_idle() > > > > to false and call rcu_enter,exit() separately. > > > > > > This approach looks quite good to me! A few comments below. > > > > But I get RCU stall warnings when running it on powerpc on top of > > the patch set at: > > > > https://lkml.org/lkml/2011/9/7/64 > > > > At first glance, it appears that CPUs are entering dyntick-idle > > mode without RCU being informed. Any thoughts on diagnostics? > > > > Thanx, Paul > > I've just tested with your rcu/next branch from github and applied > my patches on top of it but did not experience a stall in x86. Thank you for checking this! > That may be related to powerpc more precisely, or may be any arch > but on some particular condition. OK, I guess my next step is to put a WARN_ON_ONCE() in the idle loop to check to see if there might be some other idle loop buried in PowerPC somewhere... Thanx, Paul