Re: cgroup: status-quo and userland efforts

[Tim Hockin]

On Thu, Jun 27, 2013 at 11:14 AM, Serge Hallyn <serge.hallyn@xxxxxxxxxx> wrote:
> Quoting Tejun Heo (tj@xxxxxxxxxx):
>> 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.

This is something we have, partially, and are working to be able to
open-source.  We have a LOT of experience feeding into the semantics
that actually make users happy.

Today it leverages split-hierarchies, but that is not required in the
generic case (only if you want to offer the semantics we do).  It
explicitly delegates some aspects of sub-cgroup control to users, but
that could go away if your lowest-level agency can handle it.

> 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
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