You can use the ondemand cpu-freq governor, as long as you set the ignore_nice_load parameter to 1.
From Documentation/cpu-freq/governors.txt, ondemand section:
ignore_nice_load: this parameter takes a value of '0' or '1'. When
set to '0' (its default), all processes are counted towards the
'cpu utilisation' value. When set to '1', the processes that are
run with a 'nice' value will not count (and thus be ignored) in the
overall usage calculation. This is useful if you are running a CPU
intensive calculation on your laptop that you do not care how long it
takes to complete as you can 'nice' it and prevent it from taking part
in the deciding process of whether to increase your CPU frequency.
The proportion of the processor time a particular process receives is determined by the relative difference in niceness between it and other runnable processes.
The Linux Completely Fair Scheduler (CFS) calculates a weight based on the niceness. The weight is roughly equivalent to 1024 / (1.25 ^ nice_value). As the nice value decreases the weight increases exponentially. The timeslice allocated for the process is proportional to the weight of the process divided by the total weight of all runnable processes. The implementation of the CFS is in kernel/sched/fair.c.
The CFS has a target latency for the scheduling duration. Smaller target latencies yield better interactivity, but as the target latency decreases, the switching overhead increases, thus decreasing the overall throughput.
Given for instance a target latency of 20 milliseconds and two runnable processes of equal niceness, then both processes will run for 10 milliseconds each before being pre-empted in favour of the the other process. If there are 10 processes of equal niceness, each runs for 2 milliseconds each.
Now consider two processes, one with a niceness of 0 (the default), the other with a niceness of 5. The proportional difference between the corresponding weights is roughly 1/3, meaning that the higher priority process receives a timeslice of approximately 15 milliseconds while the lower priority process receives a timeslice of 5 milliseconds.
Lastly consider two processes with the niceness values of 5 and 10 respectively. While the absolute niceness is larger in this case, the relative differences between the niceness values is the same as in the previous example, yielding an identical timeslice division.
Best Answer
CPULimit is exactly what you need. You start the program, then run cpulimit against the program name or PID, specifying what percentage you want it limited.
The following command limits the process at PID 7777 to 5% CPU usage.
Alternatively, you can use the name of the executable:
Or the absolute path of the executable:
Note the percentage is of all cores; so if you have 4 cores, you could use 400%.