From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757080Ab2DTOp7 (ORCPT ); Fri, 20 Apr 2012 10:45:59 -0400 Received: from smtp11.smtpout.orange.fr ([80.12.242.133]:23877 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757020Ab2DTOpz convert rfc822-to-8bit (ORCPT ); Fri, 20 Apr 2012 10:45:55 -0400 Message-ID: <4F91769B.7000709@wanadoo.fr> Date: Fri, 20 Apr 2012 16:45:47 +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: <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> <4F8ED6FE.1000104@wanadoo.fr> <20120418152301.GF6034@linux.vnet.ibm.com> In-Reply-To: <20120418152301.GF6034@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 17:23, Paul E. McKenney a écrit : >> 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 ? > > Is it possible that systemd is using network operations that include > synchronize_rcu()? Then if you did the same operation from the > command line at runtime, you might not see the slowdown. > > Is it possible for you to convince systemd to collect RCU event tracing > during the slow operation? RCU event tracing is available under > /sys/kernel/debug/tracing/rcu. > - Paul, thank you for these suggestions : I'll manage to enable RCU event tracing immediately after mounting debugfs (systemd permits custom units). As debugfs is mounted early in the boot sequence, maybe I'll catch something. Pascal