netdev - Re: [PATCH] Traffic control cgroups subsystem

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Date:	Thu, 24 Jul 2008 21:18:21 -0400
From:	"Paul Menage" <menage@...gle.com>
To:	"Thomas Graf" <tgraf@...g.ch>
Cc:	"Ranjit Manomohan" <ranjitm@...gle.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	lizf@...fujitsu.com, kaber@...sh.net
Subject: Re: [PATCH] Traffic control cgroups subsystem

On Thu, Jul 24, 2008 at 7:45 PM, Thomas Graf <tgraf@...g.ch> wrote:
>
> It might have been easier to simply write a classifier which maps pids
> to classes. The interface could be as simple as two nested attributes,
> ADD_MAPS, REMOVE_MAPS which both take lists of pid->class mappings to
> either add or remove from the classifier.

You mean as processes fork/exit or move between cgroups you have to
update the pid->class mappings in the kernel's filter? That sounds way
too fragile to me.

>
> I have been working on this over the past 2 weeks, it includes the
> classifier as just stated, a cgroup module which sends notifications
> about events

What types of events? We discussed how to send cgroup notifications to
userspace in the containers mini-summit on Tuesday. Netlink was one of
the options discussed, but suffers from the problem that netlink
sockets are tied to a particular network namespaces. The solution that
seemed most favoured was to have pollable cgroup control files that
represent events (and optionally support event data via a fifo).

> as netlink messages and a daemon which creates qdiscs,
> classes and filters on the fly according to the configured distribution.

> It works both ingress (with some tricks) and egress.
>
> IMHO, there is no point in a cgroup interface if the user has to create
> qdiscs, classes and filters manually anyway.
>

The user can use whatever middleware they want (e.g. your daemon,
libcg, etc) to set up qdiscs and classes. I don't think that requiring
any particular userspace implementation is the right way to go. The
point of this patch was to provide a minimal way to tag
sockets/packets as belonging to a particular cgroup, in order to make
use of the existing traffic controll APIs.

Paul
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