Function cgroups_with 

pub(crate) fn cgroups_with(
    root: &Path,
    file: &str,
    set: impl Fn(&str) -> bool,
) -> (usize, Option<String>)

The request size fair.c hands out by default on this machine.

sysctl_sched_base_slice is not the 700 us the kernel is compiled with. update_sysctl() scales that at boot, and again on hotplug, by a factor taken from the number of online CPUs:

unsigned int cpus = min_t(unsigned int, num_online_cpus(), 8); case SCHED_TUNABLESCALING_LOG: factor = 1 + ilog2(cpus); sysctl_sched_base_slice = factor * normalized_sysctl_sched_base_slice;

so a machine with eight CPUs or more runs a 2.8 ms slice. This is the upstream rule with its default log scaling; a kernel whose distribution changed the normalized value or an administrator who tuned the sysctl runs fair.c at some other slice, and –slice-us is how to match it. Return the number of cgroups whose file holds a value set accepts, and one of them, walking the cgroup v2 hierarchy. A cgroup has the cpu controller’s files only where its parent enables the controller.