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How to limit CPU usage with CPULimit on Ubuntu Linux

This document describes how to limit CPU usage in Ubuntu 14.04. I will use CPU-limit utilty for this purpose. Cpulimit is a tool which limits the CPU usage of a process (expressed in percentage, not in CPU time). It is useful to control batch jobs, when you don’t want them to eat too many CPU cycles. The goal of cpulimit is to prevent a process from running for more than a specified time ratio. It does not change the nice value or other scheduling priority settings, but the real CPU usage. Also, it is able to adapt itself to the overall system load, dynamically and quickly.
The control of the used CPU amount is done sending SIGSTOP and SIGCONT POSIX signals to processes.
All the children processes and threads of the specified process will share the same percentage of CPU.

1 Preliminary Note

This tutorial is based on Ubuntu 14.04 server, so you should set up a basic Ubuntu 14.04 server installation before you continue with this tutorial. The system should have a static IP address. I use 192.168.0.100 as my IP address in this tutorial and server1.example.com as the hostname.

2 Installation

Firstly we need to install cpulimit as follows:

apt-get update
apt-get install cpulimit

3 Limiting CPU usage

Now we will check the utility for limiting the CPU usage. For this we will first check the CPU usage without cpulimit and then implement the cpulimit to evaluate the same. Lets make it clear with the example.

1. Here is an example of how to utilize your CPU with an application in single core CPU:

dd if=/dev/zero of=/dev/null

root@server1:~# dd if=/dev/zero of=/dev/null
[1] 1850
root@server1:~#

Then we will check the CPU usage with command:

top

top – 11:24:18 up 49 min,  1 user,  load average: 0.94, 1.02, 1.79
Tasks: 249 total,   2 running, 247 sleeping,   0 stopped,   0 zombie
%Cpu(s): 13.4 us, 11.6 sy,  0.0 ni, 74.9 id,  0.0 wa,  0.1 hi,  0.0 si,  0.0 st
KiB Mem:   1010540 total,   271652 used,   738888 free,    21760 buffers
KiB Swap:  1048572 total,        0 used,  1048572 free.   158204 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
1850 root      20   0    7224    616    520 R 100.0  0.1   1:20.33 dd
1851 root      20   0   24952   1756   1180 R   0.3  0.2   0:00.03 top
1 root      20   0   33480   2776   1456 S   0.0  0.3   0:05.31 init
2 root      20   0       0      0      0 S   0.0  0.0   0:00.01 kthreadd

As we can see that CPU usage have gone 100%, now we will use the cpulimit to limit the CPU usage. We can bring up this process to foreground using fg and cancel it with CTRL+C

fg

root@server1:~#

Now we can test cpulimit to see if it actually does what it is supposed to. Let test it as follows:

cpulimit -l 30 dd if=/dev/zero of=/dev/null

Now we will check the CPU usage with top command:

top

Now you can see  that the CPU usage have decreased from 100% to 33.8% almost 30%. So we have successfully checked the utility cpulimit which is able to limit the usage of CPU consumption in a single core Ubuntu distro.

2. Here is an example of how to utilize your CPU with an application in multiple core CPU:

For checking your CPU core use the command:

nproc

 In my case it is CPU core count was 4.
Now we will proceed to check the CPU usage without cpulimit in all 4 cores for the an application as follows:

for j in `seq 1 4`; do dd if=/dev/zero of=/dev/null done

It will run the command utilizing all the cores and yeild the output as:

Now check the CPU usage with top command:

top

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
1263 root      20   0    7224    612    520 R 100.0  0.1   2:21.40 dd
1264 root      20   0    7224    616    520 R 100.0  0.1   2:21.41 dd
1265 root      20   0    7224    612    520 R  99.0  0.1   2:21.03 dd
1266 root      20   0    7224    616    520 R  98.0  0.1   2:20.82 dd
1281 root      20   0  104416   3992   2920 S   1.0  0.4   0:00.03 sshd
1283 root      20   0  104416   3988   2920 S   1.0  0.4   0:00.03 sshd
1279 root      20   0  104556   4008   2924 S   0.7  0.4   0:00.08 sshd

The dd command is consuming almost 100% CPU of all the cores.  Next we will check the command with the cpulimit utility. For this kill previous traces for the dd command as follows:

killall dd

Now use cpulimit with the same command as follows:

for j in `seq 1 4`; do cpulimit -l 20 dd if=/dev/zero of=/dev/null done

[1]   Done                    cpulimit -l 20 dd if=/dev/zero of=/dev/null
[2]   Done                    cpulimit -l 20 dd if=/dev/zero of=/dev/null
[3]-  Done                    cpulimit -l 20 dd if=/dev/zero of=/dev/null
[4]+  Done                    cpulimit -l 20 dd if=/dev/zero of=/dev/null
root@server1:~#

Now check the CPU usage wit the cpulimit utility.

top

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
1433 root      20   0    7224    612    520 T  28.2  0.1   0:12.00 dd
1439 root      20   0    7224    616    520 R  26.6  0.1   0:12.13 dd
1434 root      20   0    7224    612    520 T  25.3  0.1   0:11.97 dd
1437 root      20   0    7224    612    516 T  22.9  0.1   0:11.93 dd
7 root      20   0       0      0      0 S   0.3  0.0   0:00.22 rcu_sched
8 root      20   0       0      0      0 S   0.3  0.0   0:00.21 rcuos/0

As you can see above that the CPU usage is limited from 100%  to 20% almost for multiple core CPUs.

Congratulations! We have successfully tested the cpulimit for limiting the CPU usage in Ubuntu 14.04 🙂

4 Links

•     Ubuntu : http://www.ubuntu.com/
•     cpulimit : https://github.com/opsengine/cpulimit