From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760336AbZEMOyL (ORCPT ); Wed, 13 May 2009 10:54:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755816AbZEMOx4 (ORCPT ); Wed, 13 May 2009 10:53:56 -0400 Received: from mx2.redhat.com ([66.187.237.31]:41869 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755558AbZEMOx4 (ORCPT ); Wed, 13 May 2009 10:53:56 -0400 Date: Wed, 13 May 2009 10:51:27 -0400 From: Vivek Goyal To: Gui Jianfeng Cc: nauman@google.com, dpshah@google.com, lizf@cn.fujitsu.com, mikew@google.com, fchecconi@gmail.com, paolo.valente@unimore.it, jens.axboe@oracle.com, ryov@valinux.co.jp, fernando@oss.ntt.co.jp, s-uchida@ap.jp.nec.com, taka@valinux.co.jp, jmoyer@redhat.com, dhaval@linux.vnet.ibm.com, balbir@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, containers@lists.linux-foundation.org, righi.andrea@gmail.com, agk@redhat.com, dm-devel@redhat.com, snitzer@redhat.com, m-ikeda@ds.jp.nec.com, akpm@linux-foundation.org Subject: Re: [PATCH 07/18] io-controller: Export disk time used and nr sectors dipatched through cgroups Message-ID: <20090513145127.GB7696@redhat.com> References: <1241553525-28095-1-git-send-email-vgoyal@redhat.com> <1241553525-28095-8-git-send-email-vgoyal@redhat.com> <4A0A32CB.4020609@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A0A32CB.4020609@cn.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 13, 2009 at 10:39:07AM +0800, Gui Jianfeng wrote: > Vivek Goyal wrote: > ... > > > > +/* > > + * traverse through all the io_groups associated with this cgroup and calculate > > + * the aggr disk time received by all the groups on respective disks. > > + */ > > +static u64 calculate_aggr_disk_time(struct io_cgroup *iocg) > > +{ > > + struct io_group *iog; > > + struct hlist_node *n; > > + u64 disk_time = 0; > > + > > + rcu_read_lock(); > > This function is in slow-path, so no need to call rcu_read_lock(), just need to ensure > that the caller already holds the iocg->lock. > Or can we get rid of requirement of iocg_lock here and just read the io group data under rcu read lock? Actually I am wondering why do we require an iocg_lock here. We are not modifying the rcu protected list. We are just traversing through it and reading the data. Thanks Vivek > > + hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) { > > + /* > > + * There might be groups which are not functional and > > + * waiting to be reclaimed upon cgoup deletion. > > + */ > > + if (rcu_dereference(iog->key)) > > + disk_time += iog->entity.total_service; > > + } > > + rcu_read_unlock(); > > + > > + return disk_time; > > +} > > + > > -- > Regards > Gui Jianfeng