linux-kernel - Re: Understanding cgroups

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Message-ID: <AANLkTimrSxANNzYF3AYf1uhC3SGW7c3Tf=ksBn-QUobP@mail.gmail.com>
Date:	Thu, 28 Oct 2010 19:39:44 +0200
From:	Dhaval Giani <dhaval.giani@...il.com>
To:	Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Menage <menage@...gle.com>,
	containers@...ts.linux-foundation.org,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: Understanding cgroups

[Adding a few more people and the containers to the copy]

On Thu, Oct 28, 2010 at 5:44 PM, Tommaso Cucinotta
<tommaso.cucinotta@...up.it> wrote:
> Hi,
>
> I'm trying to get some understanding of the current cgroups in-kernel
> implementation
> (after having read Documentation/cgroup* and having browsed a bit the code).
> To this purpose, I tried to draw the relationships among the involved data
> structures
> (I'm limited to its relationship with [real-time] scheduling), and obtained
> this:
>
>  http://retis.sssup.it/~tommaso/cgroups.odg
>  http://retis.sssup.it/~tommaso/cgroups.eps
>
> (You can see in the bottom left part of the diagram a little
> "key/legend/pattern" for representing lists).
>
> I might have done mistakes, however the greatest doubts that I have now
> concern the relative
> cardinalities of the various associated items. Namely:
> a) why doesn't a cgroup object directly point to a css_set one, but to a
> list of them (via cg_cgroup_list elements) ?
>    it seems that a cgroup object may be associated to multiple css_set
> objects, which in turn contain vectors of
>    cgroup_subsys_state;
> b) however, cgroup.subsys[] would point to a single cgroup_subsys_state
> object per subsys_id, so, what is the
>    difference between cgroup.subsys[] and css_set.subsys[] ? (or, are these
> all redundant pointers and point
>    to the same cgroup_subsys_state objects ?)
> c) is css_set.cg_links used to point to (the head of) a list of
> cg_cgroup_link objects, or is it used to link multiple css_set objects into
> a list ? In the latter case, where is the head of the list pointed to from ?
>
> Apologies for the newbie questions that I might have posted; FYI, I'm trying
> to set-up RT scheduling groups without using the VFS-based cgroups
> interface.
>
> Thanks in advance, regards (please, reply in cc to my e-mail address).
>
>    Tommaso
>
> --
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