[systemd-devel] systemd219 and Realtime priority

[Lukas Nykryn]

Hi!

I think you should contact the Red Hat support with this question. Most of
the distribution have CONFIG_RT_GROUP_SCHED disabled since in the general
use cases people don't use it at all. RHEL is an exception here, since we
keep that feature on, despite the recommendation of upstream, to cover some
weird use-cases.

You also might want to look at https://access.redhat.com/articles/3696121

Lukas



čt 7. 11. 2019 v 18:15 odesílatel Jon Sykes <jono.sykes15 at gmail.com> napsal:

> Hi,
>
> I'm using RHEL7 with systemd-219-62.el7_6.6.x86_64. I've recently hit an
> issue whereby a process started by a systemd service cannot assign itself
> realtime priority. Digging into the issue it seems that it is because
> systemd starts all services within a cpu/system.slice/<service_name> cgroup
> which by default wont be allocated any rt runtime through
> the cpu.rt_runtime_us value.
>
> I searched for info on how to solve this issue and came across
> https://www.freedesktop.org/wiki/Software/systemd/MyServiceCantGetRealtime/ unfortunately
> 2 of the 3 suggestions don't seem to be valid anymore:
>
> - /etc/systemd/system.conf and set DefaultControllers=
> This appears to have been removed as an option. When I tried this it had
> no effect
>
> - edit your service file, and add ControlGroup=cpu:/ to its [Service]
>  section
> This doesn't appear to be a valid option anymore:
> https://bugzilla.redhat.com/show_bug.cgi?id=999986
>
> This only leaves the option of setting cpu.rt_runtime_us value for the
> unit, however, there are a number of reasons why this isn't ideal and if
> the root cgroup config changes at any point then the value I choose isn't
> guaranteed to do what I had intended. (as pointed out in:
> https://lists.freedesktop.org/archives/systemd-devel/2015-March/029144.html
> )
>
> Is there any other way to get my service to run within a cgroup that
> allows it to assign itself realtime priority? It would seem preferable to
> be able to just run the service in the root cgroup - is this possible
> through configuration?
>
> Thanks
> Jon
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