From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753293Ab1JLNDy (ORCPT ); Wed, 12 Oct 2011 09:03:54 -0400 Received: from mail-wy0-f174.google.com ([74.125.82.174]:58983 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752859Ab1JLNDw (ORCPT ); Wed, 12 Oct 2011 09:03:52 -0400 Date: Wed, 12 Oct 2011 15:03:47 +0200 From: Frederic Weisbecker To: Glauber Costa Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, paul@paulmenage.org, lizf@cn.fujitsu.com, daniel.lezcano@free.fr, jbottomley@parallels.com Subject: Re: [PATCH 05/10] Make total_forks per-cgroup Message-ID: <20111012130344.GF14968@somewhere> References: <1317583287-18300-1-git-send-email-glommer@parallels.com> <1317583287-18300-6-git-send-email-glommer@parallels.com> <1317805535.6766.6.camel@twins> <4E8C4990.1050704@parallels.com> <20111011234548.GB14968@somewhere> <4E954356.2000409@parallels.com> <20111012125857.GE14968@somewhere> <4E958F1B.80605@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4E958F1B.80605@parallels.com> 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, Oct 12, 2011 at 04:59:07PM +0400, Glauber Costa wrote: > On 10/12/2011 04:59 PM, Frederic Weisbecker wrote: > >On Wed, Oct 12, 2011 at 11:35:50AM +0400, Glauber Costa wrote: > >>On 10/12/2011 03:45 AM, Frederic Weisbecker wrote: > >>>On Wed, Oct 05, 2011 at 04:12:00PM +0400, Glauber Costa wrote: > >>>>On 10/05/2011 01:05 PM, Peter Zijlstra wrote: > >>>>>On Sun, 2011-10-02 at 23:21 +0400, Glauber Costa wrote: > >>>>>>This patch counts the total number of forks per-cgroup. > >>>>>>The information is propagated to the parent, so the total > >>>>>>number of forks in the system, is the parent cgroup's one. > >>>>>> > >>>>>>To achieve that, total_forks is made per-cpu. There is no > >>>>>>particular reason to do that, but by doing this, we are > >>>>>>able to bundle it inside the cpustat structure already > >>>>>>present. > >>>>> > >>>>>I think fweisbec is also doing something with forks and cgroups. > >>>> > >>>>I am all ears... > >>>> > >>>>Frederic, does it conflict with what you're doing ? > >>> > >>>I don't know if that really conflicts but I'm working > >>>on a cgroup subsystem that is able to control the number > >>>of tasks running in a subsystem. > >>> > >>>It consists in two new files added: > >>> > >>>* tasks.usage > >>>* tasks.limit > >>> > >>>The subsystem rejects any new fork or migration into the > >>>cgroup when tasks.usage> tasks.limit > >>> > >>>So tasks.usage can inform you about the number of tasks > >>>running into the cgroup. It's not strictly the number > >>>of forks because it also counts the tasks that have been > >>>attached to the cgroup. > >>> > >>>But something like a tasks.fork file could be implemented > >>>in that subsystem as well. > >>> > >>>It depends on what you need. > >> > >>So the specific piece I am working on, is to display /proc/stat > >>information per-cgroup. One of the many fields it has, is > >>total_forks. > >>(it is actually just a small part of the series) > >>So instead of tracking how many forks the system has in total, I'll > >>track it per-cpucgroup. > >> > >>So I don't think we conflict at all. At the very least, IIUC, you > >>are planning to account and check *before* a fork happens, right? > >>This particular stat is incremented after it already succeeded. > > > >That doesn't make much difference since the accounting is cancelled > >in case the fork is finally rejected. > > > >But probably having a simple accouting like you do involves less > >overhead than the whole task counter subsystem. > > > >Is your counting propagated to the parents in a hierarchy? > >For example if A is parent cgroup of B and C, does A account the > >forks happening in B and C? > > Yes. But only to the first parent or also all ancestors?