Table of Contents
cpusets
Cpusets is a Linux kernel facility and a subset of cgroups-v1, that provides a mechanism to assign a set of CPUs and NUMA memory nodes (if NUMA is available) to a set of tasks. This means in effect, that the tasks are constrained to the assigned cpusets. For a detailed documentation of cpusets, please refer to the CPUSETS kernel doc.
Enable cpusets
The following kernel configuration Parameter are required to enable cpusets:
- CONFIG_CGROUPS
- CONFIG_CPUSETS
Sysfs interface
To handle the cpusets in userspace, the functionality is available in sysfs: “/sys/fs/cgroup/cpuset/”. Each cpuset is represented by a directory in the cgroup file system containing (on top of the standard cgroup files) the following files describing that cpuset:
- cpus: list of CPUs in that cpuset
- mems: list of Memory Nodes in that cpuset
- memory_migrate flag: if set, move pages to cpusets nodes
- cpu_exclusive flag: is cpu placement exclusive?
- mem_exclusive flag: is memory placement exclusive?
- mem_hardwall flag: is memory allocation hardwalled
- memory_pressure: measure of how much paging pressure in cpuset
- memory_spread_page flag: if set, spread page cache evenly on allowed nodes
- memory_spread_slab flag: if set, spread slab cache evenly on allowed nodes
- sched_load_balance flag: if set, load balance within CPUs on that cpuset
- sched_relax_domain_level: the searching range when migrating tasks
In addition, the root cpuset only has the following file:
- memory_pressure_enabled flag: compute memory_pressure?
Realtime Example
The following bash commands show exemplary how cpusets can be used for realtime processes on a 4 CPU machine. To simplify the use of cpusets the Python tool cset can be used.
$ mkdir /dev/cpuset/rt0 $ echo 0 > /dev/cpuset/rt0/cpus $ echo 0 > /dev/cpuset/rt0/mems $ echo 1 > /dev/cpuset/rt0/cpu_exclusive $ echo $RT_PROC_PID > /dev/cpuset/rt0/tasks $ mkdir /dev/cpuset/system $ echo 1-3 > /dev/cpuset/system/cpus $ echo 0 > /dev/cpuset/system/mems $ echo 1 > /dev/cpuset/system/cpu_exclusive $ for pid in $(cat /dev/cpuset/tasks); do /bin/echo $pid > /dev/cpuset/system/tasks; done
References
