Re: cgroup: status-quo and userland efforts

[Serge Hallyn <serge.hallyn@ubuntu.com>]

Quoting Tejun Heo (tj@kernel.org):
> Hello, Serge.
> 
> On Thu, Jun 27, 2013 at 08:22:06AM -0500, Serge Hallyn wrote:
> > At some point (probably soon) we might want to talk about a standard API
> > for these things.  However I think it will have to come in the form of
> > a standard library, which knows to either send requests over dbus to
> > systemd, or over /dev/cgroup sock to the manager.
> 
> Yeah, eventually, I think we'll have a standardized way to configure
> resource distribution in the system.  Maybe we'll agree on a
> standardized dbus protocol or there will be library, I don't know;
> however, whatever form it may be in, it abstraction level should be
> way higher than that of direct cgroupfs access.  It's way too low
> level and very easy to end up in a complete nonsense configuration.
> 
> e.g. enabling "cpu" on a cgroup whlie leaving other cgroups alone
> wouldn't enable fair scheduling on that cgroup but drastically reduce
> the amount of cpu share it gets as it now gets treated as single
> entity competing with all tasks at the parent level.

Right.  I *think* this can be offered as a daemon which sits as the
sole consumer of my agent's API, and offers a higher level "do what I
want" API.  But designing that API is going to be interesting.

I should find a good, up-to-date summary of the current behaviors of
each controller so I can talk more intelligently about it.  (I'll
start by looking at the kernel Documentation/cgroups, but don't
feel too confident that they'll be uptodate :)

> At the moment, I'm not sure what the eventual abstraction would look
> like.  systemd is extending its basic constructs by adding slices and
> scopes and it does make sense to integrate the general organization of
> the system (services, user sessions, VMs and so on) with resource
> management.  Given some time, I'm hoping we'll be able to come up with
> and agree on some common constructs so that each workload can indicate
> its resource requirements in a unified way.
> 
> That said, I really think we should experiment for a while before
> trying to settle down on things.  We've now just started exploring how
> system-wide resource managment can be made widely available to systems
> without requiring extremely specialized hand-crafted configurations
> and I'm pretty sure we're getting and gonna get quite a few details
> wrong, so I don't think it'd be a good idea to try to agree on things
> right now.  As far as such integration goes, I think it's time to play
> with things and observe the results.

Right,  I'm not attached to my toy implementation at all - except for
the ability, in some fashion, to have nested agents which don't have
cgroupfs access but talk to another agent to get the job done.

-serge