As opções CGroup do systemd são documentadas em 'man systemd.exec. Parece que o que você está procurando é:
'CPUWeight='
Assign the specified CPU time weight to the processes executed, if the unified control group hierarchy is used on the system. These options take an integer value and control the "cpu.weight" control group attribute. The allowed range is 1 to 10000. Defaults to 100. For details about this control group attribute, see cgroup-v2.txt[2] and sched-design-CFS.txt[5]. The available CPU time is split up among all units within one slice relative to their CPU time weight.