Chapter 26. Using cgroupfs to manually manage cgroups You can manage cgroup hierarchies on your system by creating directories on the cgroupfs virtual file system. The file system is mounted by default on the /sys/fs/cgroup/ directory and you can specify desired configurations in dedicated control files. Important In general, Red Hat recommends you use systemd for controlling the usage of system resources. You should manually configure the cgroups virtual file system only in special cases. For example, when you need to use cgroup-v1 controllers that have no equivalents in cgroup-v2 hierarchy. 26.1. Creating cgroups and enabling controllers in cgroups-v2 file system You can manage the control groups ( cgroups ) by creating or removing directories and by writing to files in the cgroups virtual file system. The file system is by default mounted on the /sys/fs/cgroup/ directory. To use settings from the cgroups controllers, you also need to enable the desired controllers for child cgroups . The root cgroup has, by default, enabled the memory and pids controllers for its child cgroups . Therefore, Red Hat recommends to create at least two levels of child cgroups inside the /sys/fs/cgroup/ root cgroup . This way you optionally remove the memory and pids controllers from the child cgroups and maintain better organizational clarity of cgroup files. Prerequisites You have root permissions. Procedure Create the /sys/fs/cgroup/Example/ directory: The /sys/fs/cgroup/Example/ directory defines a child group. When you create the /sys/fs/cgroup/Example/ directory, some cgroups-v2 interface files are automatically created in the directory. The /sys/fs/cgroup/Example/ directory contains also controller-specific files for the memory and pids controllers. Optional: Inspect the newly created child control group: The example output shows general cgroup control interface files such as cgroup.procs or cgroup.controllers . These files are common to all control groups, regardless of enabled controllers. The files such as memory.high and pids.max relate to the memory and pids controllers, which are in the root control group ( /sys/fs/cgroup/ ), and are enabled by default by systemd . By default, the newly created child group inherits all settings from the parent cgroup . In this case, there are no limits from the root cgroup . Verify that the desired controllers are available in the /sys/fs/cgroup/cgroup.controllers file: Enable the desired controllers. In this example it is cpu and cpuset controllers: These commands enable the cpu and cpuset controllers for the immediate child groups of the /sys/fs/cgroup/ root control group. Including the newly created Example control group. A child group is where you can specify processes and apply control checks to each of the processes based on your criteria. Users can read the contents of the cgroup.subtree_control file at any level to get an idea of what controllers are going to be available for enablement in the immediate child group. Note By default, the /sys/fs/cgroup/cgroup.subtree_control file in the root control group contains memory and pids controllers. Enable the desired controllers for child cgroups of the Example control group: This command ensures that the immediate child control group will only have controllers relevant to regulate the CPU time distribution - not to memory or pids controllers. Create the /sys/fs/cgroup/Example/tasks/ directory: The /sys/fs/cgroup/Example/tasks/ directory defines a child group with files that relate purely to cpu and cpuset controllers. You can now assign processes to this control group and utilize cpu and cpuset controller options for your processes. Optional: Inspect the child control group: Important The cpu controller is only activated if the relevant child control group has at least 2 processes which compete for time on a single CPU. Verification Optional: confirm that you have created a new cgroup with only the desired controllers active: Additional resources What are kernel resource controllers Mounting cgroups-v1 cgroups(7) , sysfs(5) manual pages 26.2. Controlling distribution of CPU time for applications by adjusting CPU weight You need to assign values to the relevant files of the cpu controller to regulate distribution of the CPU time to applications under the specific cgroup tree. Prerequisites You have root permissions. You have applications for which you want to control distribution of CPU time. You created a two level hierarchy of child control groups inside the /sys/fs/cgroup/ root control group as in the following example: You enabled the cpu controller in the parent control group and in child control groups similarly as described in Creating cgroups and enabling controllers in cgroups-v2 file system . Procedure Configure desired CPU weights to achieve resource restrictions within the control groups: Add the applications' PIDs to the g1 , g2 , and g3 child groups: The example commands ensure that desired applications become members of the Example/g*/ child cgroups and will get their CPU time distributed as per the configuration of those cgroups. The weights of the children cgroups ( g1 , g2 , g3 ) that have running processes are summed up at the level of the parent cgroup ( Example ). The CPU resource is then distributed proportionally based on the respective weights. As a result, when all processes run at the same time, the kernel allocates to each of them the proportionate CPU time based on their respective cgroup's cpu.weight file: Child cgroup cpu.weight file CPU time allocation g1 150 ~50% (150/300) g2 100 ~33% (100/300) g3 50 ~16% (50/300) The value of the cpu.weight controller file is not a percentage. If one process stopped running, leaving cgroup g2 with no running processes, the calculation would omit the cgroup g2 and only account weights of cgroups g1 and g3 : Child cgroup cpu.weight file CPU time allocation g1 150 ~75% (150/200) g3 50 ~25% (50/200) Important If a child cgroup has multiple running processes, the CPU time allocated to the cgroup is distributed equally among its member processes. Verification Verify that the applications run in the specified control groups: The command output shows the processes of the specified applications that run in the Example/g*/ child cgroups. Inspect the current CPU consumption of the throttled applications: Note All processes run on a single CPU for clear illustration. The CPU weight applies the same principles when used on multiple CPUs. Notice that the CPU resource for the PID 33373 , PID 33374 , and PID 33377 was allocated based on the 150, 100, and 50 weights you assigned to the respective child cgroups. The weights correspond to around 50%, 33%, and 16% allocation of CPU time for each application. 26.3. Mounting cgroups-v1 During the boot process, RHEL 9 mounts the cgroup-v2 virtual filesystem by default. To utilize cgroup-v1 functionality in limiting resources for your applications, manually configure the system. Note Both cgroup-v1 and cgroup-v2 are fully enabled in the kernel. There is no default control group version from the kernel point of view, and is decided by systemd to mount at startup. Prerequisites You have root permissions. Procedure Configure the system to mount cgroups-v1 by default during system boot by the systemd system and service manager: This adds the necessary kernel command-line parameters to the current boot entry. To add the same parameters to all kernel boot entries: Reboot the system for the changes to take effect. Verification Verify that the cgroups-v1 filesystem was mounted: The cgroups-v1 filesystems that correspond to various cgroup-v1 controllers, were successfully mounted on the /sys/fs/cgroup/ directory. Inspect the contents of the /sys/fs/cgroup/ directory: The /sys/fs/cgroup/ directory, also called the root control group , by default, contains controller-specific directories such as cpuset . In addition, there are some directories related to systemd . Additional resources What are kernel resource controllers cgroups(7) , sysfs(5) manual pages cgroup-v2 enabled by default in RHEL 9 26.4. Setting CPU limits to applications using cgroups-v1 To configure CPU limits to an application by using control groups version 1 ( cgroups-v1 ), use the /sys/fs/ virtual file system. Prerequisites You have root permissions. You have an application to restrict its CPU consumption installed on your system. You configured the system to mount cgroups-v1 by default during system boot by the systemd system and service manager: This adds the necessary kernel command-line parameters to the current boot entry. Procedure Identify the process ID (PID) of the application that you want to restrict in CPU consumption: The sha1sum example application with PID 6955 consumes a large amount of CPU resources. Create a sub-directory in the cpu resource controller directory: This directory represents a control group, where you can place specific processes and apply certain CPU limits to the processes. At the same time, a number of cgroups-v1 interface files and cpu controller-specific files will be created in the directory. Optional: Inspect the newly created control group: Files, such as cpuacct.usage , cpu.cfs._period_us represent specific configurations and/or limits, which can be set for processes in the Example control group. Note that the file names are prefixed with the name of the control group controller they belong to. By default, the newly created control group inherits access to the system's entire CPU resources without a limit. Configure CPU limits for the control group: The cpu.cfs_period_us file represents how frequently a control group's access to CPU resources must be reallocated. The time period is in microseconds (ms, "us"). The upper limit is 1 000 000 microseconds and the lower limit is 1000 microseconds. The cpu.cfs_quota_us file represents the total amount of time in microseconds for which all processes in a control group can collectively run during one period, as defined by cpu.cfs_period_us . When processes in a control group use up all the time specified by the quota during a single period, they are throttled for the remainder of the period and not allowed to run until the period. The lower limit is 1000 microseconds. The example commands above set the CPU time limits so that all processes collectively in the Example control group will be able to run only for 0.2 seconds (defined by cpu.cfs_quota_us ) out of every 1 second (defined by cpu.cfs_period_us ). Optional: Verify the limits: Add the application's PID to the Example control group: This command ensures that a specific application becomes a member of the Example control group and does not exceed the CPU limits configured for the Example control group. The PID must represent an existing process in the system. The PID 6955 here was assigned to the sha1sum /dev/zero & process, used to illustrate the use case of the cpu controller. Verification Verify that the application runs in the specified control group: The process of an application runs in the Example control group applying CPU limits to the application's process. Identify the current CPU consumption of your throttled application: Note that the CPU consumption of the PID 6955 has decreased from 99% to 20%. Note The cgroups-v2 counterpart for cpu.cfs_period_us and cpu.cfs_quota_us is the cpu.max file. The cpu.max file is available through the cpu controller. Additional resources Introducing kernel resource controllers cgroups(7) , sysfs(5) manual pages

Commands:
mkdir /sys/fs/cgroup/Example/
ll /sys/fs/cgroup/Example/ -r- r- r--. 1 root root 0 Jun 1 10:33 cgroup.controllers -r- r- r--. 1 root root 0 Jun 1 10:33 cgroup.events -rw-r- r--. 1 root root 0 Jun 1 10:33 cgroup.freeze -rw-r- r--. 1 root root 0 Jun 1 10:33 cgroup.procs ... -rw-r- r--. 1 root root 0 Jun 1 10:33 cgroup.subtree_control -r- r- r--. 1 root root 0 Jun 1 10:33 memory.events.local -rw-r- r--. 1 root root 0 Jun 1 10:33 memory.high -rw-r- r--. 1 root root 0 Jun 1 10:33 memory.low ... -r- r- r--. 1 root root 0 Jun 1 10:33 pids.current -r- r- r--. 1 root root 0 Jun 1 10:33 pids.events -rw-r- r--. 1 root root 0 Jun 1 10:33 pids.max
cat /sys/fs/cgroup/cgroup.controllers cpuset cpu io memory hugetlb pids rdma
echo "+cpu" >> /sys/fs/cgroup/cgroup.subtree_control echo "+cpuset" >> /sys/fs/cgroup/cgroup.subtree_control
echo "+cpu +cpuset" >> /sys/fs/cgroup/Example/cgroup.subtree_control
mkdir /sys/fs/cgroup/Example/tasks/
ll /sys/fs/cgroup/Example/tasks -r- r- r--. 1 root root 0 Jun 1 11:45 cgroup.controllers -r- r- r--. 1 root root 0 Jun 1 11:45 cgroup.events -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.freeze -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.max.depth -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.max.descendants -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.procs -r- r- r--. 1 root root 0 Jun 1 11:45 cgroup.stat -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.subtree_control -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.threads -rw-r- r--. 1 root root 0 Jun 1 11:45 cgroup.type -rw-r- r--. 1 root root 0 Jun 1 11:45 cpu.max -rw-r- r--. 1 root root 0 Jun 1 11:45 cpu.pressure -rw-r- r--. 1 root root 0 Jun 1 11:45 cpuset.cpus -r- r- r--. 1 root root 0 Jun 1 11:45 cpuset.cpus.effective -rw-r- r--. 1 root root 0 Jun 1 11:45 cpuset.cpus.partition -rw-r- r--. 1 root root 0 Jun 1 11:45 cpuset.mems -r- r- r--. 1 root root 0 Jun 1 11:45 cpuset.mems.effective -r- r- r--. 1 root root 0 Jun 1 11:45 cpu.stat -rw-r- r--. 1 root root 0 Jun 1 11:45 cpu.weight -rw-r- r--. 1 root root 0 Jun 1 11:45 cpu.weight.nice -rw-r- r--. 1 root root 0 Jun 1 11:45 io.pressure -rw-r- r--. 1 root root 0 Jun 1 11:45 memory.pressure
cat /sys/fs/cgroup/Example/tasks/cgroup.controllers cpuset cpu
... ├── Example │ ├── g1 │ ├── g2 │ └── g3 ...
echo "150" > /sys/fs/cgroup/Example/g1/cpu.weight echo "100" > /sys/fs/cgroup/Example/g2/cpu.weight echo "50" > /sys/fs/cgroup/Example/g3/cpu.weight
echo "33373" > /sys/fs/cgroup/Example/g1/cgroup.procs echo "33374" > /sys/fs/cgroup/Example/g2/cgroup.procs echo "33377" > /sys/fs/cgroup/Example/g3/cgroup.procs
cat /proc/33373/cgroup /proc/33374/cgroup /proc/33377/cgroup 0::/Example/g1 0::/Example/g2 0::/Example/g3
top top - 05:17:18 up 1 day, 18:25, 1 user, load average: 3.03, 3.03, 3.00 Tasks: 95 total, 4 running, 91 sleeping, 0 stopped, 0 zombie %Cpu(s): 18.1 us, 81.6 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.3 hi, 0.0 si, 0.0 st MiB Mem : 3737.0 total, 3233.7 free, 132.8 used, 370.5 buff/cache MiB Swap: 4060.0 total, 4060.0 free, 0.0 used. 3373.1 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 33373 root 20 0 18720 1748 1460 R 49.5 0.0 415:05.87 sha1sum 33374 root 20 0 18720 1756 1464 R 32.9 0.0 412:58.33 sha1sum 33377 root 20 0 18720 1860 1568 R 16.3 0.0 411:03.12 sha1sum 760 root 20 0 416620 28540 15296 S 0.3 0.7 0:10.23 tuned 1 root 20 0 186328 14108 9484 S 0.0 0.4 0:02.00 systemd 2 root 20 0 0 0 0 S 0.0 0.0 0:00.01 kthread
grubby --update-kernel=/boot/vmlinuz-USD(uname -r) --args="systemd.unified_cgroup_hierarchy=0 systemd.legacy_systemd_cgroup_controller"
grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=0 systemd.legacy_systemd_cgroup_controller"
mount -l | grep cgroup tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,seclabel,size=4096k,nr_inodes=1024,mode=755,inode64) cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd) cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,perf_event) cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,cpu,cpuacct) cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,pids) cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,cpuset) cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,net_cls,net_prio) cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,hugetlb) cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,memory) cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,blkio) cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,devices) cgroup on /sys/fs/cgroup/misc type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,misc) cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,freezer) cgroup on /sys/fs/cgroup/rdma type cgroup (rw,nosuid,nodev,noexec,relatime,seclabel,rdma)
ll /sys/fs/cgroup/ dr-xr-xr-x. 10 root root 0 Mar 16 09:34 blkio lrwxrwxrwx. 1 root root 11 Mar 16 09:34 cpu cpu,cpuacct lrwxrwxrwx. 1 root root 11 Mar 16 09:34 cpuacct cpu,cpuacct dr-xr-xr-x. 10 root root 0 Mar 16 09:34 cpu,cpuacct dr-xr-xr-x. 2 root root 0 Mar 16 09:34 cpuset dr-xr-xr-x. 10 root root 0 Mar 16 09:34 devices dr-xr-xr-x. 2 root root 0 Mar 16 09:34 freezer dr-xr-xr-x. 2 root root 0 Mar 16 09:34 hugetlb dr-xr-xr-x. 10 root root 0 Mar 16 09:34 memory dr-xr-xr-x. 2 root root 0 Mar 16 09:34 misc lrwxrwxrwx. 1 root root 16 Mar 16 09:34 net_cls net_cls,net_prio dr-xr-xr-x. 2 root root 0 Mar 16 09:34 net_cls,net_prio lrwxrwxrwx. 1 root root 16 Mar 16 09:34 net_prio net_cls,net_prio dr-xr-xr-x. 2 root root 0 Mar 16 09:34 perf_event dr-xr-xr-x. 10 root root 0 Mar 16 09:34 pids dr-xr-xr-x. 2 root root 0 Mar 16 09:34 rdma dr-xr-xr-x. 11 root root 0 Mar 16 09:34 systemd
grubby --update-kernel=/boot/vmlinuz-USD(uname -r) --args="systemd.unified_cgroup_hierarchy=0 systemd.legacy_systemd_cgroup_controller"
top top - 11:34:09 up 11 min, 1 user, load average: 0.51, 0.27, 0.22 Tasks: 267 total, 3 running, 264 sleeping, 0 stopped, 0 zombie %Cpu(s): 49.0 us, 3.3 sy, 0.0 ni, 47.5 id, 0.0 wa, 0.2 hi, 0.0 si, 0.0 st MiB Mem : 1826.8 total, 303.4 free, 1046.8 used, 476.5 buff/cache MiB Swap: 1536.0 total, 1396.0 free, 140.0 used. 616.4 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 6955 root 20 0 228440 1752 1472 R 99.3 0.1 0:32.71 sha1sum 5760 jdoe 20 0 3603868 205188 64196 S 3.7 11.0 0:17.19 gnome-shell 6448 jdoe 20 0 743648 30640 19488 S 0.7 1.6 0:02.73 gnome-terminal- 1 root 20 0 245300 6568 4116 S 0.3 0.4 0:01.87 systemd 505 root 20 0 0 0 0 I 0.3 0.0 0:00.75 kworker/u4:4-events_unbound
mkdir /sys/fs/cgroup/cpu/Example/
ll /sys/fs/cgroup/cpu/Example/ -rw-r- r--. 1 root root 0 Mar 11 11:42 cgroup.clone_children -rw-r- r--. 1 root root 0 Mar 11 11:42 cgroup.procs -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.stat -rw-r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage_all -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage_percpu -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage_percpu_sys -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage_percpu_user -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage_sys -r- r- r--. 1 root root 0 Mar 11 11:42 cpuacct.usage_user -rw-r- r--. 1 root root 0 Mar 11 11:42 cpu.cfs_period_us -rw-r- r--. 1 root root 0 Mar 11 11:42 cpu.cfs_quota_us -rw-r- r--. 1 root root 0 Mar 11 11:42 cpu.rt_period_us -rw-r- r--. 1 root root 0 Mar 11 11:42 cpu.rt_runtime_us -rw-r- r--. 1 root root 0 Mar 11 11:42 cpu.shares -r- r- r--. 1 root root 0 Mar 11 11:42 cpu.stat -rw-r- r--. 1 root root 0 Mar 11 11:42 notify_on_release -rw-r- r--. 1 root root 0 Mar 11 11:42 tasks
echo "1000000" > /sys/fs/cgroup/cpu/Example/cpu.cfs_period_us echo "200000" > /sys/fs/cgroup/cpu/Example/cpu.cfs_quota_us
cat /sys/fs/cgroup/cpu/Example/cpu.cfs_period_us /sys/fs/cgroup/cpu/Example/cpu.cfs_quota_us 1000000 200000
echo "6955" > /sys/fs/cgroup/cpu/Example/cgroup.procs
cat /proc/6955/cgroup 12:cpuset:/ 11:hugetlb:/ 10:net_cls,net_prio:/ 9:memory:/user.slice/user-1000.slice/user@1000.service 8:devices:/user.slice 7:blkio:/ 6:freezer:/ 5:rdma:/ 4:pids:/user.slice/user-1000.slice/user@1000.service 3:perf_event:/ 2:cpu,cpuacct:/Example 1:name=systemd:/user.slice/user-1000.slice/user@1000.service/gnome-terminal-server.service
top top - 12:28:42 up 1:06, 1 user, load average: 1.02, 1.02, 1.00 Tasks: 266 total, 6 running, 260 sleeping, 0 stopped, 0 zombie %Cpu(s): 11.0 us, 1.2 sy, 0.0 ni, 87.5 id, 0.0 wa, 0.2 hi, 0.0 si, 0.2 st MiB Mem : 1826.8 total, 287.1 free, 1054.4 used, 485.3 buff/cache MiB Swap: 1536.0 total, 1396.7 free, 139.2 used. 608.3 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 6955 root 20 0 228440 1752 1472 R 20.6 0.1 47:11.43 sha1sum 5760 jdoe 20 0 3604956 208832 65316 R 2.3 11.2 0:43.50 gnome-shell 6448 jdoe 20 0 743836 31736 19488 S 0.7 1.7 0:08.25 gnome-terminal- 505 root 20 0 0 0 0 I 0.3 0.0 0:03.39 kworker/u4:4-events_unbound 4217 root 20 0 74192 1612 1320 S 0.3 0.1 0:01.19 spice-vdagentd