[systemd-devel] systemd and cgroups

[Colin Guthrie]

Hello,

You're approaching this whole thread from a fixed position and therefore
seem to be seeing *everything* as negative and problematic.

Rather than coming here with problem and looking for a solution, you've
arrived with a solution already designed and seem to be complaining that
it won't work.

There WILL be a solution to your *problem* but it might not be achieved
via the design you have in mind.

It could be due to the semantics of how you express the requirement
means you have to think about the problem differently.

Much of what you say below is simply incompatible with the upstream
kernel single-cgroup manager model that is being pushed. You cannot have
a "custom cgroup configuration" directly under this model: the
configuration has to be expressed indirectly as user and administrator
friendly declarative statements in various unit files which ultimately
map to cgroup configurations (mostly as an implementation detail).


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

Well, this has obviously given everyone the time to properly respond and
help you with your problem. If I didn't know better this whole
conversation would appear to be just a random complaint FUD email rather
than one seeking to gain knowledge.

>>> 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. 

That is completely untrue. You have read far too much into that
statement and the examples provided there. Let Lennart answer for
himself before you make rash generalisations.

> So sure, according to that mail, the goal of the crgoup interface of
> systemd is just to run a GUI

Completely untrue and certainly not how I read the email.

> 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.

Yes, it's another issue and one *completely* irrelevant to this mailing
list. Such negativity in comments is *highly unwelcome* here. Please
keep it to yourself or for slashdot posts.

> 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.

Quite possibly. Complaining that nobody held your hand here is somewhat
off topic however. It doesn't change the fact that the documentation for
systemd is extremely extensive and one of the best documented open
source projects I've ever worked with.

> 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.

No, systemd is designed to *manage* your custom cgroup configurations.
It abstracts cgroups away to pretty much an implementation detail. You
can still get the needed *solution* to your problem.

> 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.

Keep in mind that the single-writer principle is still relatively new.
Everything has to be adapted to it and systemd has moved very quickly to
match the upstream kernel needs. As time goes on, documentation in this
area will improve.

>>> 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.

Your "choice" exists in your ability to view, understand and write the
code yourself. Whether someone's crazy whim or configuration (not
necessarily referring to your current requirement) has to be supported
by every utility in the open source stack is completely different.
People hear the word "choice" and build up a whole expectation around
it's dictionary definition to the extent that they presume everyone must
bend over backwards to support any crazy idea they come up with. I'm
sorry, but this has never and will never be true.

http://islinuxaboutchoice.com/

>> 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.

This is impossible. The kernel is moving to a single cgroup writer and
systemd makes extensive use of cgroups internally. Such a setup option
would be orthogonal to both the kernel and systemd itself.

>>  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.

I'm sure if you do, you'll realise that you simply won't be able to keep
your current solution as is defined now. You will have to adapt to
getting the same end result via a different path in the end.

Good luck with it, but please try to keep an open mind and try not to
phrase things with an "I've already decided that I'm right and everyone
else is wrong" kind of attitude. It does not make people want to offer
advice or reply and you'll ultimately get a negative experience. It's a
self fulfilling prophesy. If you start off with a negative attitude
you'll ultimately come away with a negative experience. If you come in
with an open mind and ask open questions, you'll likely find a very
engaging and useful discussion forms as a result.

Col


-- 

Colin Guthrie
gmane(at)colin.guthr.ie
http://colin.guthr.ie/

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