Chapter 27. Using cgroupfs to manually manage cgroups

Procedure

1. Create the /sys/fs/cgroup/Example/ directory:

   # mkdir /sys/fs/cgroup/Example/

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   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.

2. Optional: Inspect the newly created child control group:

   # 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

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   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.

3. Verify that the desired controllers are available in the /sys/fs/cgroup/cgroup.controllers file:

   # cat /sys/fs/cgroup/cgroup.controllers
   cpuset cpu io memory hugetlb pids rdma

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4. Enable the desired controllers. In this example it is cpu and cpuset controllers:

   # echo "+cpu" >> /sys/fs/cgroup/cgroup.subtree_control
   # echo "+cpuset" >> /sys/fs/cgroup/cgroup.subtree_control

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   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.

5. Enable the desired controllers for child cgroups of the Example control group:

   # echo "+cpu +cpuset" >> /sys/fs/cgroup/Example/cgroup.subtree_control

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   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.

6. Create the /sys/fs/cgroup/Example/tasks/ directory:

   # mkdir /sys/fs/cgroup/Example/tasks/

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   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.

7. Optional: Inspect the child control group:

   # 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

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Procedure

1. Configure desired CPU weights to achieve resource restrictions within the control groups:

   # 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

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2. Add the applications' PIDs to the g1, g2, and g3 child groups:

   # 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

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   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:

   Expand

   Child cgroup	cpu.weight file	CPU time allocation
   g1	150	~50% (150/300)
   g2	100	~33% (100/300)
   g3	50	~16% (50/300)

   Show more

   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:

   Expand

   Child cgroup	cpu.weight file	CPU time allocation
   g1	150	~75% (150/200)
   g3	50	~25% (50/200)

   Show more
   Important

   If a child cgroup has multiple running processes, the CPU time allocated to the cgroup is distributed equally among its member processes.

Verification

1. Verify that the applications run in the specified control groups:

   # cat /proc/33373/cgroup /proc/33374/cgroup /proc/33377/cgroup
   0::/Example/g1
   0::/Example/g2
   0::/Example/g3

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   The command output shows the processes of the specified applications that run in the Example/g*/ child cgroups.

2. Inspect the current CPU consumption of the throttled applications:

   # 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
   ...

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   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.

Procedure

1. Configure the system to mount cgroups-v1 by default during system boot by the systemd system and service manager:

   # grubby --update-kernel=/boot/vmlinuz-$(uname -r) --args="systemd.unified_cgroup_hierarchy=0 systemd.legacy_systemd_cgroup_controller"

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   This adds the necessary kernel command-line parameters to the current boot entry.

   To add the same parameters to all kernel boot entries:

   # grubby --update-kernel=ALL --args="systemd.unified_cgroup_hierarchy=0 systemd.legacy_systemd_cgroup_controller"

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2. Reboot the system for the changes to take effect.

Verification

1. Verify that the cgroups-v1 filesystem was mounted:

   # 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)

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   The cgroups-v1 filesystems that correspond to various cgroup-v1 controllers, were successfully mounted on the /sys/fs/cgroup/ directory.

2. Inspect the contents of the /sys/fs/cgroup/ directory:

   # 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

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   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.

Procedure

1. Identify the process ID (PID) of the application that you want to restrict in CPU consumption:

   # 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
   ...

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   The sha1sum example application with PID 6955 consumes a large amount of CPU resources.

2. Create a sub-directory in the cpu resource controller directory:

   # mkdir /sys/fs/cgroup/cpu/Example/

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   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.

3. Optional: Inspect the newly created control group:

   # 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

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   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.

4. Configure CPU limits for the control group:

   # echo "1000000" > /sys/fs/cgroup/cpu/Example/cpu.cfs_period_us
   # echo "200000" > /sys/fs/cgroup/cpu/Example/cpu.cfs_quota_us

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   • 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 (µs, "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 next 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).

5. Optional: Verify the limits:

   # cat /sys/fs/cgroup/cpu/Example/cpu.cfs_period_us /sys/fs/cgroup/cpu/Example/cpu.cfs_quota_us
   1000000
   200000

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6. Add the application’s PID to the Example control group:

   # echo "6955" > /sys/fs/cgroup/cpu/Example/cgroup.procs

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   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

1. Verify that the application runs in the specified control group:

   # 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

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   The process of an application runs in the Example control group applying CPU limits to the application’s process.

2. Identify the current CPU consumption of your throttled application:

   # 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
   ...

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   Note that the CPU consumption of the PID 6955 has decreased from 99% to 20%.