Search code examples
dbussystemdcgroupsgdbus

systemd resource control SetProperties with gdbus at runtime

I have a systemd foo.slice with cgroup setting CPUShares. My idea is to change the setting at certain point during the system startup, which will be triggered by a systemd service.

I do some test work to check how to change the setting at runtime.

In the foo.slice I defined CPUShares=256. Which will cause cat /sys/fs/cgroup/cpu/foo.slice/cpu.shares 256.

And will get the following lines by gdbus introspect:

interface org.freedesktop.systemd1.Slice {
  methods:
  signals:
  properties:
    @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
    readonly s Slice = '-.slice';
    @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
    readonly s ControlGroup = '/foo.slice';
    @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
    readonly b CPUAccounting = false;
    @org.freedesktop.DBus.Property.EmitsChangedSignal("false")
    readonly t CPUShares = 256;

I try to change the CPUShares by invoking the method:

@org.freedesktop.systemd1.Privileged("true")
SetProperties(in  b arg_0,
              in  a(sv) arg_1);

using:

gdbus call --system --dest org.freedesktop.systemd1 --object-path /org/freedesktop/systemd/unit/foo_2eslice --method org.freedesktop.systemd1.Unit.SetProperties true "[('CPUShares', <@t 2048>)]"

And I will get

@org.freedesktop.DBus.Property.EmitsChangedSignal("false")
readonly t CPUShares = 2048;

But I still get cat /sys/fs/cgroup/cpu/foo.slice/cpu.shares 256.

After I restart the slice:

gdbus call --system --dest org.freedesktop.systemd1 --object-path /org/freedesktop/systemd1/unit/foo_2eslice --method org.freedesktop.systemd1.Unit.Restart 'replace'

I will get cat /sys/fs/cgroup/cpu/foo.slice/cpu.shares 2048

I use systemd 211.

I wish to know more detail about this behavior or if there are better solutions, i.e. wish to get some hint to change the CPUShares at runtime with systemd.

Solution

  • If you are trying to change the cpu shares before systemd reaches its default.target you need to use StartupCPUShares=.