Playing with processes on Linux is always fun. cpulimit and taskset are two cool and useful utilities to control the behaviour of your processes at a CPU-core level.
cpulimit
Lets you control or limit the CPU usage of a process. This will make a processor intensive process take longer to finish but will allow other processes to utilize the CPU. cpulimit works on both single or multi-core environments. Run the following command to install cpulimit on Ubuntu:
$ sudo apt-get install cpulimit
The easiest way to use cpulimit is to add cpulimit -l perecentage_of_cpu before your usual command. For example:
$ cpulimit -l 20 ghb
will run HandBrake (ghb) and force it to use around 20% of your processing capacity. cpulimit has options to attach to an already running process:
-p PID : attach to the process with PID process ID $ cpulimit -l 20 -p 1234 -e prog_name : attach to the executable with name prog_name $ cpulimit -l 20 -e ghb
The -b option runs cpulimit in the background.
taskset
taskset is a wrapper to the sched_setaffinity system call. Use it to control which processor core(s) a process can run on.
To start HandBrake on cores 0, 2 and 3:
$ taskset -c 0,2,3 ghb
To make a process with PID 1234 run on cores 0 and 2 (the output will show the current and changed affinity):
$ taskset -c -p 0,2 1234 //note: 0,2 comes after -p followed by PID pid 1234's current affinity list: 0-3 pid 1234's new affinity list: 0,2
As you can see, before changing the affinity, the process could have run on any core from 0 to 3 (I have a quad core device). That’s the general affinity of any process started without taskset.
To know the current affinity of any process:
$ taskset -c -p PID
You can also use ps:
$ ps -o pid,psr,comm -p PID