[systemd-devel] service fails to use the latest value of the slice

[Tiwari, Hari Sahaya]

Hello,
I have one query on the behaviour I am overserving with systemd service.

Below are the contents of service file,

# cat /usr/lib/systemd/system/qs.service
[Unit]
Description=init script
After=network.target

[Service]
ExecStartPre=/bin/sh /usr/local/cmcluster/bin/realtimeslice.sh -s /usr/lib/systemd/system/qs.service
ExecStart=/usr/local/qs/bin/qs
Type=simple

[Install]
WantedBy=multi-user.target

What realtimeslice.sh does is to identify a slice having RT quantum (cpu.rt_runtime_us) as 950000.
Once the slice is identified the service attaches the binary mentioned in ExecStart to that slice.
This is done because binary(/usr/local/qs/bin/qs) tries to set realtime priority.

Now coming to the issue which I am facing,


1.     Suppose I have 2 slices, A.slice (cpu.rt_runtime_us value = 950000) and B.slice (cpu.rt_runtime_us  value = 0)

2.     Currently the service qs.service is attached to A.slice

3.     Now I changed cpu.rt_runtime_us values for these slices:  A.slice to 0 and B.slice to 950000.

4.     When I restart the service, ExecStartPre (i.e realtimeslice.sh) determines that B.slice is eligible slice and it updates the slice name in the configuration files and in drop-ins.

5.     But Binary at ExecStart still doesn't see the updated slice info and fails to set the realtime priority.

6.     If I restart the service again it is working fine and binary is able to set the realtime priority.

Is it that systemd at its invocation caches the all the information (including slice values) and uses those values for ExecStart[Pre] ? Because in the next run it is working fine.

Is there a way reload/refresh the settings done at ExecStartPre, so that it will reflect at ExecStart.

Thanks & Regards,
Hari.


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