[systemd-devel] Setting low-level cgroups attributes in systemd

[Joe Miller]

Understood. Thank you for the explanation. I'm not familiar with the cgroup
rework being done so I don't have any ideas or opinion on that at the
moment.

I was not aware of %c. It sounds like that might be a reasonable and simple
workaround for now.

thanks


On Tue, Dec 10, 2013 at 9:24 AM, Lennart Poettering
<lennart at poettering.net>wrote:

> On Mon, 09.12.13 10:31, Joe Miller (joeym at joeym.net) wrote:
>
> > It appears that the .slice changed described here[1] removed all ability
> to
> > set low-level cgroups settings, is that correct?
>
> Yes, that is correct. With the new code only attributes that systemd
> understands can be set, nothing else.
>
> > For cgroup attributes that systemd does not natively support
> > (example: cpu.cfs_period_us and cpu.cfs_quota_us) it was previously
> > possible to set these
> >
> > 1. via unit files:  ControlGroupAttribute=cpu.cfs_period_us 500
> > 2. or at runtime:  systemctl --runtime set-cgroup-attr thing.service
> > cpu.cfs_period_us 500
> >
> > I find the ability to set cgroup attrs not supported natively by systemd
> > useful, will this be added back to systemd or will systemd support all
> > cgroup attributes?
>
> The problem with supporting these generic attributes is that they all
> have very different semantics how they can be reset and what writing to
> them actually does (some overwrite previous settings, others are lists
> that the new data you write is appended to, even others work more like a
> dictionary). Also, a big chunk of them are going to go away with Tejun's
> "sane behaviour" cgroup rework.
>
> We are happy to support more options high-level in systemd, however,
> there needs to be a clear perspective that they are options that are
> going to stay. The last time we discussed the cfs attributes in
> particular Tejun indicated they wouldn't stay the way they are.
>
> Now, if there at least is a clear perspective how they are going to look
> like in future in the kernel, then we can add support for them now
> already and add a bit of compat code that tries to translate them to the
> old cgroup kernel api, but I am not sure whether that is possible for
> the cfs attributes.
>
> A dirty work-around for the time being is to simply set these properties
> via a shell fragment. You can use the "%c" specifier which will tell you
> the cgroup path of a service, use that in some ExecStartPre= script that
> initializes these for you.
>
> If you'd like to see proper support for this stuff (which I certainly
> want), then we need to discuss with Tejun how we can expose these props
> already now.
>
> Lennart
>
> --
> Lennart Poettering, Red Hat
>
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