From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753771Ab2DRPAV (ORCPT ); Wed, 18 Apr 2012 11:00:21 -0400 Received: from smtp01.smtpout.orange.fr ([80.12.242.123]:24066 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750808Ab2DRPAT convert rfc822-to-8bit (ORCPT ); Wed, 18 Apr 2012 11:00:19 -0400 Message-ID: <4F8ED6FE.1000104@wanadoo.fr> Date: Wed, 18 Apr 2012 17:00:14 +0200 From: Pascal Chapperon User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Josh Boyer , linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org Subject: Re: RCU related performance regression in 3.3 References: <20120405123759.GE1963@zod.bos.redhat.com> <20120405140006.GB27672@linux.vnet.ibm.com> <1838583439.163624.1333635333132.JavaMail.www@wwinf1m19> <20120405143918.GE27672@linux.vnet.ibm.com> <588810225.17969.1333703883646.JavaMail.www@wwinf1g24> <20120410160706.GF2428@linux.vnet.ibm.com> <4F859E0E.8050408@wanadoo.fr> <20120412180432.GE2394@linux.vnet.ibm.com> <20120416210234.GA3490@linux.vnet.ibm.com> <4F8E8B58.1040203@wanadoo.fr> <20120418140108.GA6034@linux.vnet.ibm.com> In-Reply-To: <20120418140108.GA6034@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 18/04/2012 16:01, Paul E. McKenney a écrit : > On Wed, Apr 18, 2012 at 11:37:28AM +0200, Pascal Chapperon wrote: >> Mount and umount operations are not slower with RCU_FAST_NO_HZ during >> runtime; systemctl start and stop operations are also not slower. In >> fact, i couldn't find a single operation slower during runtime with >> RCU_FAST_NO_HZ. > > Your boot-time setup is such that all CPUs are online before the > boot-time mount operations take place, right? Yes : [ 0.242697] Brought up 8 CPUs [ 0.242699] Total of 8 processors activated (35118.33 BogoMIPS). > Struggling to understand > how RCU can tell the difference between post-CPU-bringup boot time > and run time... > systemd is controlling the whole boot process including mount operation (apart root filesystem) and as I can see, uses heavily sockets to do it (not to mention cpu-affinity). It controls also the major part of umount operations. Is it possible that your patch hits a systemd bug ? What I don't understand is that systemd coexists well with RCU_FAST_NO_HZ on a smaller laptop with older and much less powerful cpu. I'll do further tests on another machine. Pascal