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It's also a > writable control on root, which we otherwise keep off root. Well, /proc/sys/kernel/sched_rt_{runtime,period}_us control the total fraction of CPU time that can be reserved for dl and rt tasks; here, we need a way to reserve a part of this fraction for rt cgropus only. We need this because "regular" dl entities (the ones serving dl tasks) are "global" (can migrate between different CPU cores), whereas dl entities serving rt cgroups are pinned to their own CPU cores. Combining the admission tests for these two different kinds of dl entities is not simple, so we reserve a fixed fraction of CPU time for rt cgroups, and the remaining part of sched_rt_runtime_us/sched_rt_period_us is left to dl tasks. If there is a better interface we can use to achieve this goal, we are happy to switch to it. Thanks, Luca