[systemd-devel] systemd and cgroups

[Dominique Michel]

Le Sun, 12 Jan 2014 16:07:45 -0800,
Greg KH <gregkh at linuxfoundation.org> a écrit :

> On Sun, Jan 12, 2014 at 11:48:56PM +0100, Dominique Michel wrote:
> > I need that pc for production, so I rapidly installed another
> > distribution without systemd. So this problem is solved for me, but
> > that doesn't solve that to force any user to use a default
> > configuration without any possibility of user setup, and without
> > documentation that can allow an user to do that, is just a design
> > fault.
> 
> That sounds like a distro issue, please take this up with your distro
> developers, this isn't a systemd issue.

Too late, I shifted the distribution because I was in urgent need of a
good working system on that box.

> 
> > Again, the point of the cgroups is to be able to adapt the system to
> > any kind of workload, and to have systemd that take control of that
> > good and flexible system, and at the same time, doesn't provide
> > a way for an user to adapt the default configuration to its own
> > need, is just a big design bug, which start with Lennart failure to
> > take in account the fact that all users are corner cases by
> > definition, because all users are doing different kind of works with
> > their computers.
> 
> That's not the goak of cgroups at all, sorry.

Lennart is very clear in his email, "normal" users run a GUI. Sorry,
but I am not abnormal and I do some work with my computer. The GUI is
just an accessory for me, and as long it is not in my way and provide
me a decent mouse focus policy and plenty of keyboard short cuts, 2
things essential for my work flow, I am happy with it.

So sure, according to that mail, the goal of the crgoup interface of
systemd is just to run a GUI, and this is precisely why it doesn't work
for me: it doesn't allow custom cgroup configuration for people that
want to do something more than running a GUI.

And yes, as I want (my choice) a GUI that is not in my way, I am
allergic to a GUI that interfere with a good working system (like gnome
and its *kit madness), but that's another issue.

> 
> > Today, during a forum discussion on the cgroups, someone gave
> > the link above with the different Lennart's statements. I begun to
> > understand. Later also today, I finally find some documentation on
> > the freedesktop web site. But that's too late, I need this pc for
> > production, and I have other things to do than risking a hard disk
> > failure because of a freezing system, so I will not reinstall
> > Debian. And for that, I didn't even read more of that doc than a few
> > lines. I just lost the interest of the good idea that systemd is,
> > that because of its catastrophic implementation that can cause so
> > severe regression like system freeze, and its almost complete lack
> > of documentation. 
> 
> I don't think you have looked, systemd is the best documented piece of
> software I've ever seen.

The fact is that nobody on the Debian forum was able to help me, or
even aware of the existence of that documentation. Or they all was in
holiday at that time.

Anyway, I did read it but was completely unable to make it to work,
whatever I try. It is only when I read Lennart email yesterday, I
understand why it was not working: systemd is designed to not work with
custom cgroup configurations. The least you could do is to tell that in
the documentation. I wasted a few weeks with that.

And if it is already stated in the doc that systemd will not work with
custom cgroup configurations, you must emphasis more on that issue, so
that worried users doesn't miss it, and doesn't waste their time with
this.

> 
> > So, don't say me I could have done this or that, that's not my
> > point. My major point is GNU/Linux have always been about choices,
> 
> That's not true at all, it's never been about choices.

Well, you don't need to say anything more, we just don't have the
same conception of Free Software. For me, Free Software is about 5
fundamental liberties, and liberty is all about choices.

> 
> > and the actual systemd implementation and lack of documentation is
> > just removing the possibility for the user to choose what he want do
> > with the cgroups, which can break the whole system apart when he try
> > to do its own cgroup configuration.
> 
> If you wish to use your own cgroup configurations, yes, I would
> suggest not using systemd.

It is what I have done after formatting and checking my drive. And
that's the real problem, systemd is not compatible with custom cgroup
configuration. I hope this will change in the future, because this is a
choice (again!) I made to use a custom cgroup configuration. And I am
sure I am not the only one into a similar case.

As an alternative, systemd should at least provide a setup option for
it to not interfere with an existing cgroup configuration.
 
>  But please work with the kernel cgroup
> developers, as the cgroup interface is going to be changing quite a
> bit in the future.

OK, I will do it.

> 
> This really has nothing to do with systemd on it's own, sorry.
> Please talk with your distro developers if you are unhappy with their
> design decisions.

Again, if systemd is not able to deal with a custom cgroup
configuration, it could at least provide a setup or an option to not
interfere with an existing cgroup configuration. 

Anyway, I don't know why systemd was installed, because on a lot of
other Debian systems, it is not the case. And I shifted to gentoo, so
this issue is solved for me. But it remain that systemd is not only
unable to deal with custom cgroup configurations, it just break them.

Best Regards,
Dominique

> 
> best of luck,
> 
> greg k-h