From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753029Ab3ABQoZ (ORCPT ); Wed, 2 Jan 2013 11:44:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:62787 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752989Ab3ABQoX (ORCPT ); Wed, 2 Jan 2013 11:44:23 -0500 Date: Wed, 2 Jan 2013 11:44:15 -0500 From: Vivek Goyal To: Tejun Heo Cc: lizefan@huawei.com, axboe@kernel.dk, containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, ctalbott@google.com, rni@google.com Subject: Re: [PATCH 23/24] cfq-iosched: collect stats from dead cfqgs Message-ID: <20130102164415.GB4306@redhat.com> References: <1356726946-26037-1-git-send-email-tj@kernel.org> <1356726946-26037-24-git-send-email-tj@kernel.org> <20130102162415.GA4306@redhat.com> <20130102163010.GC11220@mtj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130102163010.GC11220@mtj.dyndns.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 02, 2013 at 11:30:10AM -0500, Tejun Heo wrote: > Hey, Vivek. > > On Wed, Jan 02, 2013 at 11:24:15AM -0500, Vivek Goyal wrote: > > On Fri, Dec 28, 2012 at 12:35:45PM -0800, Tejun Heo wrote: > > > To support hierarchical stats, it's necessary to remember stats from > > > dead children. Add cfqg->dead_stats and make a dying cfqg transfer > > > its stats to the parent's dead-stats. > > > > Hi Tejun, > > > > Why not directly transfer stats to cfqg->stats. IOW, what's the advantage > > of maintaining dead_stats separately. > > Backward compatibility? The existing stat cgroupfs files expect to > see non-recursive stats. Oh yes. Missed that. So dead_stats makes sense. [..] > > In fact if we have a realiable way of resetting status then online/offline > > infrastructure might not be required? I think per cpu stats will be a > > problem though and that's why we probably require logic to online/offline > > the group? > > Hmmm? What do you mean? I mean if we had a reliable way of resetting stats after transferring then we would not need to keep a track of whether group is online/offline. We could add everything and adding zero will not change anything. In fact it will also take care of residual IO (IO which happened after transfer of stats). Or I missed the real reason of why do we have group online/offline infrastructure. Thanks Vivek